From 82bcbebce43f0227f506d75a5b764b6847041bae Mon Sep 17 00:00:00 2001 From: Ben Cheng Date: Mon, 1 Oct 2012 10:30:31 -0700 Subject: Initial check-in of gcc 4.7.2. Change-Id: I4a2f5a921c21741a0e18bda986d77e5f1bef0365 --- gcc-4.7/gcc/tree-ssa-loop-prefetch.c | 1946 ++++++++++++++++++++++++++++++++++ 1 file changed, 1946 insertions(+) create mode 100644 gcc-4.7/gcc/tree-ssa-loop-prefetch.c (limited to 'gcc-4.7/gcc/tree-ssa-loop-prefetch.c') diff --git a/gcc-4.7/gcc/tree-ssa-loop-prefetch.c b/gcc-4.7/gcc/tree-ssa-loop-prefetch.c new file mode 100644 index 000000000..264d97bc1 --- /dev/null +++ b/gcc-4.7/gcc/tree-ssa-loop-prefetch.c @@ -0,0 +1,1946 @@ +/* Array prefetching. + Copyright (C) 2005, 2007, 2008, 2009, 2010, 2011 + Free Software Foundation, Inc. + +This file is part of GCC. + +GCC is free software; you can redistribute it and/or modify it +under the terms of the GNU General Public License as published by the +Free Software Foundation; either version 3, or (at your option) any +later version. + +GCC is distributed in the hope that it will be useful, but WITHOUT +ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or +FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License +for more details. + +You should have received a copy of the GNU General Public License +along with GCC; see the file COPYING3. If not see +. */ + +#include "config.h" +#include "system.h" +#include "coretypes.h" +#include "tm.h" +#include "tree.h" +#include "tm_p.h" +#include "basic-block.h" +#include "output.h" +#include "tree-pretty-print.h" +#include "tree-flow.h" +#include "tree-dump.h" +#include "timevar.h" +#include "cfgloop.h" +#include "tree-pass.h" +#include "insn-config.h" +#include "recog.h" +#include "hashtab.h" +#include "tree-chrec.h" +#include "tree-scalar-evolution.h" +#include "diagnostic-core.h" +#include "params.h" +#include "langhooks.h" +#include "tree-inline.h" +#include "tree-data-ref.h" + + +/* FIXME: Needed for optabs, but this should all be moved to a TBD interface + between the GIMPLE and RTL worlds. */ +#include "expr.h" +#include "optabs.h" + +/* This pass inserts prefetch instructions to optimize cache usage during + accesses to arrays in loops. It processes loops sequentially and: + + 1) Gathers all memory references in the single loop. + 2) For each of the references it decides when it is profitable to prefetch + it. To do it, we evaluate the reuse among the accesses, and determines + two values: PREFETCH_BEFORE (meaning that it only makes sense to do + prefetching in the first PREFETCH_BEFORE iterations of the loop) and + PREFETCH_MOD (meaning that it only makes sense to prefetch in the + iterations of the loop that are zero modulo PREFETCH_MOD). For example + (assuming cache line size is 64 bytes, char has size 1 byte and there + is no hardware sequential prefetch): + + char *a; + for (i = 0; i < max; i++) + { + a[255] = ...; (0) + a[i] = ...; (1) + a[i + 64] = ...; (2) + a[16*i] = ...; (3) + a[187*i] = ...; (4) + a[187*i + 50] = ...; (5) + } + + (0) obviously has PREFETCH_BEFORE 1 + (1) has PREFETCH_BEFORE 64, since (2) accesses the same memory + location 64 iterations before it, and PREFETCH_MOD 64 (since + it hits the same cache line otherwise). + (2) has PREFETCH_MOD 64 + (3) has PREFETCH_MOD 4 + (4) has PREFETCH_MOD 1. We do not set PREFETCH_BEFORE here, since + the cache line accessed by (5) is the same with probability only + 7/32. + (5) has PREFETCH_MOD 1 as well. + + Additionally, we use data dependence analysis to determine for each + reference the distance till the first reuse; this information is used + to determine the temporality of the issued prefetch instruction. + + 3) We determine how much ahead we need to prefetch. The number of + iterations needed is time to fetch / time spent in one iteration of + the loop. The problem is that we do not know either of these values, + so we just make a heuristic guess based on a magic (possibly) + target-specific constant and size of the loop. + + 4) Determine which of the references we prefetch. We take into account + that there is a maximum number of simultaneous prefetches (provided + by machine description). We prefetch as many prefetches as possible + while still within this bound (starting with those with lowest + prefetch_mod, since they are responsible for most of the cache + misses). + + 5) We unroll and peel loops so that we are able to satisfy PREFETCH_MOD + and PREFETCH_BEFORE requirements (within some bounds), and to avoid + prefetching nonaccessed memory. + TODO -- actually implement peeling. + + 6) We actually emit the prefetch instructions. ??? Perhaps emit the + prefetch instructions with guards in cases where 5) was not sufficient + to satisfy the constraints? + + A cost model is implemented to determine whether or not prefetching is + profitable for a given loop. The cost model has three heuristics: + + 1. Function trip_count_to_ahead_ratio_too_small_p implements a + heuristic that determines whether or not the loop has too few + iterations (compared to ahead). Prefetching is not likely to be + beneficial if the trip count to ahead ratio is below a certain + minimum. + + 2. Function mem_ref_count_reasonable_p implements a heuristic that + determines whether the given loop has enough CPU ops that can be + overlapped with cache missing memory ops. If not, the loop + won't benefit from prefetching. In the implementation, + prefetching is not considered beneficial if the ratio between + the instruction count and the mem ref count is below a certain + minimum. + + 3. Function insn_to_prefetch_ratio_too_small_p implements a + heuristic that disables prefetching in a loop if the prefetching + cost is above a certain limit. The relative prefetching cost is + estimated by taking the ratio between the prefetch count and the + total intruction count (this models the I-cache cost). + + The limits used in these heuristics are defined as parameters with + reasonable default values. Machine-specific default values will be + added later. + + Some other TODO: + -- write and use more general reuse analysis (that could be also used + in other cache aimed loop optimizations) + -- make it behave sanely together with the prefetches given by user + (now we just ignore them; at the very least we should avoid + optimizing loops in that user put his own prefetches) + -- we assume cache line size alignment of arrays; this could be + improved. */ + +/* Magic constants follow. These should be replaced by machine specific + numbers. */ + +/* True if write can be prefetched by a read prefetch. */ + +#ifndef WRITE_CAN_USE_READ_PREFETCH +#define WRITE_CAN_USE_READ_PREFETCH 1 +#endif + +/* True if read can be prefetched by a write prefetch. */ + +#ifndef READ_CAN_USE_WRITE_PREFETCH +#define READ_CAN_USE_WRITE_PREFETCH 0 +#endif + +/* The size of the block loaded by a single prefetch. Usually, this is + the same as cache line size (at the moment, we only consider one level + of cache hierarchy). */ + +#ifndef PREFETCH_BLOCK +#define PREFETCH_BLOCK L1_CACHE_LINE_SIZE +#endif + +/* Do we have a forward hardware sequential prefetching? */ + +#ifndef HAVE_FORWARD_PREFETCH +#define HAVE_FORWARD_PREFETCH 0 +#endif + +/* Do we have a backward hardware sequential prefetching? */ + +#ifndef HAVE_BACKWARD_PREFETCH +#define HAVE_BACKWARD_PREFETCH 0 +#endif + +/* In some cases we are only able to determine that there is a certain + probability that the two accesses hit the same cache line. In this + case, we issue the prefetches for both of them if this probability + is less then (1000 - ACCEPTABLE_MISS_RATE) per thousand. */ + +#ifndef ACCEPTABLE_MISS_RATE +#define ACCEPTABLE_MISS_RATE 50 +#endif + +#ifndef HAVE_prefetch +#define HAVE_prefetch 0 +#endif + +#define L1_CACHE_SIZE_BYTES ((unsigned) (L1_CACHE_SIZE * 1024)) +#define L2_CACHE_SIZE_BYTES ((unsigned) (L2_CACHE_SIZE * 1024)) + +/* We consider a memory access nontemporal if it is not reused sooner than + after L2_CACHE_SIZE_BYTES of memory are accessed. However, we ignore + accesses closer than L1_CACHE_SIZE_BYTES / NONTEMPORAL_FRACTION, + so that we use nontemporal prefetches e.g. if single memory location + is accessed several times in a single iteration of the loop. */ +#define NONTEMPORAL_FRACTION 16 + +/* In case we have to emit a memory fence instruction after the loop that + uses nontemporal stores, this defines the builtin to use. */ + +#ifndef FENCE_FOLLOWING_MOVNT +#define FENCE_FOLLOWING_MOVNT NULL_TREE +#endif + +/* It is not profitable to prefetch when the trip count is not at + least TRIP_COUNT_TO_AHEAD_RATIO times the prefetch ahead distance. + For example, in a loop with a prefetch ahead distance of 10, + supposing that TRIP_COUNT_TO_AHEAD_RATIO is equal to 4, it is + profitable to prefetch when the trip count is greater or equal to + 40. In that case, 30 out of the 40 iterations will benefit from + prefetching. */ + +#ifndef TRIP_COUNT_TO_AHEAD_RATIO +#define TRIP_COUNT_TO_AHEAD_RATIO 4 +#endif + +/* The group of references between that reuse may occur. */ + +struct mem_ref_group +{ + tree base; /* Base of the reference. */ + tree step; /* Step of the reference. */ + struct mem_ref *refs; /* References in the group. */ + struct mem_ref_group *next; /* Next group of references. */ +}; + +/* Assigned to PREFETCH_BEFORE when all iterations are to be prefetched. */ + +#define PREFETCH_ALL (~(unsigned HOST_WIDE_INT) 0) + +/* Do not generate a prefetch if the unroll factor is significantly less + than what is required by the prefetch. This is to avoid redundant + prefetches. For example, when prefetch_mod is 16 and unroll_factor is + 2, prefetching requires unrolling the loop 16 times, but + the loop is actually unrolled twice. In this case (ratio = 8), + prefetching is not likely to be beneficial. */ + +#ifndef PREFETCH_MOD_TO_UNROLL_FACTOR_RATIO +#define PREFETCH_MOD_TO_UNROLL_FACTOR_RATIO 4 +#endif + +/* Some of the prefetch computations have quadratic complexity. We want to + avoid huge compile times and, therefore, want to limit the amount of + memory references per loop where we consider prefetching. */ + +#ifndef PREFETCH_MAX_MEM_REFS_PER_LOOP +#define PREFETCH_MAX_MEM_REFS_PER_LOOP 200 +#endif + +/* The memory reference. */ + +struct mem_ref +{ + gimple stmt; /* Statement in that the reference appears. */ + tree mem; /* The reference. */ + HOST_WIDE_INT delta; /* Constant offset of the reference. */ + struct mem_ref_group *group; /* The group of references it belongs to. */ + unsigned HOST_WIDE_INT prefetch_mod; + /* Prefetch only each PREFETCH_MOD-th + iteration. */ + unsigned HOST_WIDE_INT prefetch_before; + /* Prefetch only first PREFETCH_BEFORE + iterations. */ + unsigned reuse_distance; /* The amount of data accessed before the first + reuse of this value. */ + struct mem_ref *next; /* The next reference in the group. */ + unsigned write_p : 1; /* Is it a write? */ + unsigned independent_p : 1; /* True if the reference is independent on + all other references inside the loop. */ + unsigned issue_prefetch_p : 1; /* Should we really issue the prefetch? */ + unsigned storent_p : 1; /* True if we changed the store to a + nontemporal one. */ +}; + +/* Dumps information about reference REF to FILE. */ + +static void +dump_mem_ref (FILE *file, struct mem_ref *ref) +{ + fprintf (file, "Reference %p:\n", (void *) ref); + + fprintf (file, " group %p (base ", (void *) ref->group); + print_generic_expr (file, ref->group->base, TDF_SLIM); + fprintf (file, ", step "); + if (cst_and_fits_in_hwi (ref->group->step)) + fprintf (file, HOST_WIDE_INT_PRINT_DEC, int_cst_value (ref->group->step)); + else + print_generic_expr (file, ref->group->step, TDF_TREE); + fprintf (file, ")\n"); + + fprintf (file, " delta "); + fprintf (file, HOST_WIDE_INT_PRINT_DEC, ref->delta); + fprintf (file, "\n"); + + fprintf (file, " %s\n", ref->write_p ? "write" : "read"); + + fprintf (file, "\n"); +} + +/* Finds a group with BASE and STEP in GROUPS, or creates one if it does not + exist. */ + +static struct mem_ref_group * +find_or_create_group (struct mem_ref_group **groups, tree base, tree step) +{ + struct mem_ref_group *group; + + for (; *groups; groups = &(*groups)->next) + { + if (operand_equal_p ((*groups)->step, step, 0) + && operand_equal_p ((*groups)->base, base, 0)) + return *groups; + + /* If step is an integer constant, keep the list of groups sorted + by decreasing step. */ + if (cst_and_fits_in_hwi ((*groups)->step) && cst_and_fits_in_hwi (step) + && int_cst_value ((*groups)->step) < int_cst_value (step)) + break; + } + + group = XNEW (struct mem_ref_group); + group->base = base; + group->step = step; + group->refs = NULL; + group->next = *groups; + *groups = group; + + return group; +} + +/* Records a memory reference MEM in GROUP with offset DELTA and write status + WRITE_P. The reference occurs in statement STMT. */ + +static void +record_ref (struct mem_ref_group *group, gimple stmt, tree mem, + HOST_WIDE_INT delta, bool write_p) +{ + struct mem_ref **aref; + + /* Do not record the same address twice. */ + for (aref = &group->refs; *aref; aref = &(*aref)->next) + { + /* It does not have to be possible for write reference to reuse the read + prefetch, or vice versa. */ + if (!WRITE_CAN_USE_READ_PREFETCH + && write_p + && !(*aref)->write_p) + continue; + if (!READ_CAN_USE_WRITE_PREFETCH + && !write_p + && (*aref)->write_p) + continue; + + if ((*aref)->delta == delta) + return; + } + + (*aref) = XNEW (struct mem_ref); + (*aref)->stmt = stmt; + (*aref)->mem = mem; + (*aref)->delta = delta; + (*aref)->write_p = write_p; + (*aref)->prefetch_before = PREFETCH_ALL; + (*aref)->prefetch_mod = 1; + (*aref)->reuse_distance = 0; + (*aref)->issue_prefetch_p = false; + (*aref)->group = group; + (*aref)->next = NULL; + (*aref)->independent_p = false; + (*aref)->storent_p = false; + + if (dump_file && (dump_flags & TDF_DETAILS)) + dump_mem_ref (dump_file, *aref); +} + +/* Release memory references in GROUPS. */ + +static void +release_mem_refs (struct mem_ref_group *groups) +{ + struct mem_ref_group *next_g; + struct mem_ref *ref, *next_r; + + for (; groups; groups = next_g) + { + next_g = groups->next; + for (ref = groups->refs; ref; ref = next_r) + { + next_r = ref->next; + free (ref); + } + free (groups); + } +} + +/* A structure used to pass arguments to idx_analyze_ref. */ + +struct ar_data +{ + struct loop *loop; /* Loop of the reference. */ + gimple stmt; /* Statement of the reference. */ + tree *step; /* Step of the memory reference. */ + HOST_WIDE_INT *delta; /* Offset of the memory reference. */ +}; + +/* Analyzes a single INDEX of a memory reference to obtain information + described at analyze_ref. Callback for for_each_index. */ + +static bool +idx_analyze_ref (tree base, tree *index, void *data) +{ + struct ar_data *ar_data = (struct ar_data *) data; + tree ibase, step, stepsize; + HOST_WIDE_INT idelta = 0, imult = 1; + affine_iv iv; + + if (!simple_iv (ar_data->loop, loop_containing_stmt (ar_data->stmt), + *index, &iv, true)) + return false; + ibase = iv.base; + step = iv.step; + + if (TREE_CODE (ibase) == POINTER_PLUS_EXPR + && cst_and_fits_in_hwi (TREE_OPERAND (ibase, 1))) + { + idelta = int_cst_value (TREE_OPERAND (ibase, 1)); + ibase = TREE_OPERAND (ibase, 0); + } + if (cst_and_fits_in_hwi (ibase)) + { + idelta += int_cst_value (ibase); + ibase = build_int_cst (TREE_TYPE (ibase), 0); + } + + if (TREE_CODE (base) == ARRAY_REF) + { + stepsize = array_ref_element_size (base); + if (!cst_and_fits_in_hwi (stepsize)) + return false; + imult = int_cst_value (stepsize); + step = fold_build2 (MULT_EXPR, sizetype, + fold_convert (sizetype, step), + fold_convert (sizetype, stepsize)); + idelta *= imult; + } + + if (*ar_data->step == NULL_TREE) + *ar_data->step = step; + else + *ar_data->step = fold_build2 (PLUS_EXPR, sizetype, + fold_convert (sizetype, *ar_data->step), + fold_convert (sizetype, step)); + *ar_data->delta += idelta; + *index = ibase; + + return true; +} + +/* Tries to express REF_P in shape &BASE + STEP * iter + DELTA, where DELTA and + STEP are integer constants and iter is number of iterations of LOOP. The + reference occurs in statement STMT. Strips nonaddressable component + references from REF_P. */ + +static bool +analyze_ref (struct loop *loop, tree *ref_p, tree *base, + tree *step, HOST_WIDE_INT *delta, + gimple stmt) +{ + struct ar_data ar_data; + tree off; + HOST_WIDE_INT bit_offset; + tree ref = *ref_p; + + *step = NULL_TREE; + *delta = 0; + + /* First strip off the component references. Ignore bitfields. + Also strip off the real and imagine parts of a complex, so that + they can have the same base. */ + if (TREE_CODE (ref) == REALPART_EXPR + || TREE_CODE (ref) == IMAGPART_EXPR + || (TREE_CODE (ref) == COMPONENT_REF + && DECL_NONADDRESSABLE_P (TREE_OPERAND (ref, 1)))) + { + if (TREE_CODE (ref) == IMAGPART_EXPR) + *delta += int_size_in_bytes (TREE_TYPE (ref)); + ref = TREE_OPERAND (ref, 0); + } + + *ref_p = ref; + + for (; TREE_CODE (ref) == COMPONENT_REF; ref = TREE_OPERAND (ref, 0)) + { + off = DECL_FIELD_BIT_OFFSET (TREE_OPERAND (ref, 1)); + bit_offset = TREE_INT_CST_LOW (off); + gcc_assert (bit_offset % BITS_PER_UNIT == 0); + + *delta += bit_offset / BITS_PER_UNIT; + } + + *base = unshare_expr (ref); + ar_data.loop = loop; + ar_data.stmt = stmt; + ar_data.step = step; + ar_data.delta = delta; + return for_each_index (base, idx_analyze_ref, &ar_data); +} + +/* Record a memory reference REF to the list REFS. The reference occurs in + LOOP in statement STMT and it is write if WRITE_P. Returns true if the + reference was recorded, false otherwise. */ + +static bool +gather_memory_references_ref (struct loop *loop, struct mem_ref_group **refs, + tree ref, bool write_p, gimple stmt) +{ + tree base, step; + HOST_WIDE_INT delta; + struct mem_ref_group *agrp; + + if (get_base_address (ref) == NULL) + return false; + + if (!analyze_ref (loop, &ref, &base, &step, &delta, stmt)) + return false; + /* If analyze_ref fails the default is a NULL_TREE. We can stop here. */ + if (step == NULL_TREE) + return false; + + /* Stop if the address of BASE could not be taken. */ + if (may_be_nonaddressable_p (base)) + return false; + + /* Limit non-constant step prefetching only to the innermost loops. */ + if (!cst_and_fits_in_hwi (step) && loop->inner != NULL) + return false; + + /* Now we know that REF = &BASE + STEP * iter + DELTA, where DELTA and STEP + are integer constants. */ + agrp = find_or_create_group (refs, base, step); + record_ref (agrp, stmt, ref, delta, write_p); + + return true; +} + +/* Record the suitable memory references in LOOP. NO_OTHER_REFS is set to + true if there are no other memory references inside the loop. */ + +static struct mem_ref_group * +gather_memory_references (struct loop *loop, bool *no_other_refs, unsigned *ref_count) +{ + basic_block *body = get_loop_body_in_dom_order (loop); + basic_block bb; + unsigned i; + gimple_stmt_iterator bsi; + gimple stmt; + tree lhs, rhs; + struct mem_ref_group *refs = NULL; + + *no_other_refs = true; + *ref_count = 0; + + /* Scan the loop body in order, so that the former references precede the + later ones. */ + for (i = 0; i < loop->num_nodes; i++) + { + bb = body[i]; + if (bb->loop_father != loop) + continue; + + for (bsi = gsi_start_bb (bb); !gsi_end_p (bsi); gsi_next (&bsi)) + { + stmt = gsi_stmt (bsi); + + if (gimple_code (stmt) != GIMPLE_ASSIGN) + { + if (gimple_vuse (stmt) + || (is_gimple_call (stmt) + && !(gimple_call_flags (stmt) & ECF_CONST))) + *no_other_refs = false; + continue; + } + + lhs = gimple_assign_lhs (stmt); + rhs = gimple_assign_rhs1 (stmt); + + if (REFERENCE_CLASS_P (rhs)) + { + *no_other_refs &= gather_memory_references_ref (loop, &refs, + rhs, false, stmt); + *ref_count += 1; + } + if (REFERENCE_CLASS_P (lhs)) + { + *no_other_refs &= gather_memory_references_ref (loop, &refs, + lhs, true, stmt); + *ref_count += 1; + } + } + } + free (body); + + return refs; +} + +/* Prune the prefetch candidate REF using the self-reuse. */ + +static void +prune_ref_by_self_reuse (struct mem_ref *ref) +{ + HOST_WIDE_INT step; + bool backward; + + /* If the step size is non constant, we cannot calculate prefetch_mod. */ + if (!cst_and_fits_in_hwi (ref->group->step)) + return; + + step = int_cst_value (ref->group->step); + + backward = step < 0; + + if (step == 0) + { + /* Prefetch references to invariant address just once. */ + ref->prefetch_before = 1; + return; + } + + if (backward) + step = -step; + + if (step > PREFETCH_BLOCK) + return; + + if ((backward && HAVE_BACKWARD_PREFETCH) + || (!backward && HAVE_FORWARD_PREFETCH)) + { + ref->prefetch_before = 1; + return; + } + + ref->prefetch_mod = PREFETCH_BLOCK / step; +} + +/* Divides X by BY, rounding down. */ + +static HOST_WIDE_INT +ddown (HOST_WIDE_INT x, unsigned HOST_WIDE_INT by) +{ + gcc_assert (by > 0); + + if (x >= 0) + return x / by; + else + return (x + by - 1) / by; +} + +/* Given a CACHE_LINE_SIZE and two inductive memory references + with a common STEP greater than CACHE_LINE_SIZE and an address + difference DELTA, compute the probability that they will fall + in different cache lines. Return true if the computed miss rate + is not greater than the ACCEPTABLE_MISS_RATE. DISTINCT_ITERS is the + number of distinct iterations after which the pattern repeats itself. + ALIGN_UNIT is the unit of alignment in bytes. */ + +static bool +is_miss_rate_acceptable (unsigned HOST_WIDE_INT cache_line_size, + HOST_WIDE_INT step, HOST_WIDE_INT delta, + unsigned HOST_WIDE_INT distinct_iters, + int align_unit) +{ + unsigned align, iter; + int total_positions, miss_positions, max_allowed_miss_positions; + int address1, address2, cache_line1, cache_line2; + + /* It always misses if delta is greater than or equal to the cache + line size. */ + if (delta >= (HOST_WIDE_INT) cache_line_size) + return false; + + miss_positions = 0; + total_positions = (cache_line_size / align_unit) * distinct_iters; + max_allowed_miss_positions = (ACCEPTABLE_MISS_RATE * total_positions) / 1000; + + /* Iterate through all possible alignments of the first + memory reference within its cache line. */ + for (align = 0; align < cache_line_size; align += align_unit) + + /* Iterate through all distinct iterations. */ + for (iter = 0; iter < distinct_iters; iter++) + { + address1 = align + step * iter; + address2 = address1 + delta; + cache_line1 = address1 / cache_line_size; + cache_line2 = address2 / cache_line_size; + if (cache_line1 != cache_line2) + { + miss_positions += 1; + if (miss_positions > max_allowed_miss_positions) + return false; + } + } + return true; +} + +/* Prune the prefetch candidate REF using the reuse with BY. + If BY_IS_BEFORE is true, BY is before REF in the loop. */ + +static void +prune_ref_by_group_reuse (struct mem_ref *ref, struct mem_ref *by, + bool by_is_before) +{ + HOST_WIDE_INT step; + bool backward; + HOST_WIDE_INT delta_r = ref->delta, delta_b = by->delta; + HOST_WIDE_INT delta = delta_b - delta_r; + HOST_WIDE_INT hit_from; + unsigned HOST_WIDE_INT prefetch_before, prefetch_block; + HOST_WIDE_INT reduced_step; + unsigned HOST_WIDE_INT reduced_prefetch_block; + tree ref_type; + int align_unit; + + /* If the step is non constant we cannot calculate prefetch_before. */ + if (!cst_and_fits_in_hwi (ref->group->step)) { + return; + } + + step = int_cst_value (ref->group->step); + + backward = step < 0; + + + if (delta == 0) + { + /* If the references has the same address, only prefetch the + former. */ + if (by_is_before) + ref->prefetch_before = 0; + + return; + } + + if (!step) + { + /* If the reference addresses are invariant and fall into the + same cache line, prefetch just the first one. */ + if (!by_is_before) + return; + + if (ddown (ref->delta, PREFETCH_BLOCK) + != ddown (by->delta, PREFETCH_BLOCK)) + return; + + ref->prefetch_before = 0; + return; + } + + /* Only prune the reference that is behind in the array. */ + if (backward) + { + if (delta > 0) + return; + + /* Transform the data so that we may assume that the accesses + are forward. */ + delta = - delta; + step = -step; + delta_r = PREFETCH_BLOCK - 1 - delta_r; + delta_b = PREFETCH_BLOCK - 1 - delta_b; + } + else + { + if (delta < 0) + return; + } + + /* Check whether the two references are likely to hit the same cache + line, and how distant the iterations in that it occurs are from + each other. */ + + if (step <= PREFETCH_BLOCK) + { + /* The accesses are sure to meet. Let us check when. */ + hit_from = ddown (delta_b, PREFETCH_BLOCK) * PREFETCH_BLOCK; + prefetch_before = (hit_from - delta_r + step - 1) / step; + + /* Do not reduce prefetch_before if we meet beyond cache size. */ + if (prefetch_before > absu_hwi (L2_CACHE_SIZE_BYTES / step)) + prefetch_before = PREFETCH_ALL; + if (prefetch_before < ref->prefetch_before) + ref->prefetch_before = prefetch_before; + + return; + } + + /* A more complicated case with step > prefetch_block. First reduce + the ratio between the step and the cache line size to its simplest + terms. The resulting denominator will then represent the number of + distinct iterations after which each address will go back to its + initial location within the cache line. This computation assumes + that PREFETCH_BLOCK is a power of two. */ + prefetch_block = PREFETCH_BLOCK; + reduced_prefetch_block = prefetch_block; + reduced_step = step; + while ((reduced_step & 1) == 0 + && reduced_prefetch_block > 1) + { + reduced_step >>= 1; + reduced_prefetch_block >>= 1; + } + + prefetch_before = delta / step; + delta %= step; + ref_type = TREE_TYPE (ref->mem); + align_unit = TYPE_ALIGN (ref_type) / 8; + if (is_miss_rate_acceptable (prefetch_block, step, delta, + reduced_prefetch_block, align_unit)) + { + /* Do not reduce prefetch_before if we meet beyond cache size. */ + if (prefetch_before > L2_CACHE_SIZE_BYTES / PREFETCH_BLOCK) + prefetch_before = PREFETCH_ALL; + if (prefetch_before < ref->prefetch_before) + ref->prefetch_before = prefetch_before; + + return; + } + + /* Try also the following iteration. */ + prefetch_before++; + delta = step - delta; + if (is_miss_rate_acceptable (prefetch_block, step, delta, + reduced_prefetch_block, align_unit)) + { + if (prefetch_before < ref->prefetch_before) + ref->prefetch_before = prefetch_before; + + return; + } + + /* The ref probably does not reuse by. */ + return; +} + +/* Prune the prefetch candidate REF using the reuses with other references + in REFS. */ + +static void +prune_ref_by_reuse (struct mem_ref *ref, struct mem_ref *refs) +{ + struct mem_ref *prune_by; + bool before = true; + + prune_ref_by_self_reuse (ref); + + for (prune_by = refs; prune_by; prune_by = prune_by->next) + { + if (prune_by == ref) + { + before = false; + continue; + } + + if (!WRITE_CAN_USE_READ_PREFETCH + && ref->write_p + && !prune_by->write_p) + continue; + if (!READ_CAN_USE_WRITE_PREFETCH + && !ref->write_p + && prune_by->write_p) + continue; + + prune_ref_by_group_reuse (ref, prune_by, before); + } +} + +/* Prune the prefetch candidates in GROUP using the reuse analysis. */ + +static void +prune_group_by_reuse (struct mem_ref_group *group) +{ + struct mem_ref *ref_pruned; + + for (ref_pruned = group->refs; ref_pruned; ref_pruned = ref_pruned->next) + { + prune_ref_by_reuse (ref_pruned, group->refs); + + if (dump_file && (dump_flags & TDF_DETAILS)) + { + fprintf (dump_file, "Reference %p:", (void *) ref_pruned); + + if (ref_pruned->prefetch_before == PREFETCH_ALL + && ref_pruned->prefetch_mod == 1) + fprintf (dump_file, " no restrictions"); + else if (ref_pruned->prefetch_before == 0) + fprintf (dump_file, " do not prefetch"); + else if (ref_pruned->prefetch_before <= ref_pruned->prefetch_mod) + fprintf (dump_file, " prefetch once"); + else + { + if (ref_pruned->prefetch_before != PREFETCH_ALL) + { + fprintf (dump_file, " prefetch before "); + fprintf (dump_file, HOST_WIDE_INT_PRINT_DEC, + ref_pruned->prefetch_before); + } + if (ref_pruned->prefetch_mod != 1) + { + fprintf (dump_file, " prefetch mod "); + fprintf (dump_file, HOST_WIDE_INT_PRINT_DEC, + ref_pruned->prefetch_mod); + } + } + fprintf (dump_file, "\n"); + } + } +} + +/* Prune the list of prefetch candidates GROUPS using the reuse analysis. */ + +static void +prune_by_reuse (struct mem_ref_group *groups) +{ + for (; groups; groups = groups->next) + prune_group_by_reuse (groups); +} + +/* Returns true if we should issue prefetch for REF. */ + +static bool +should_issue_prefetch_p (struct mem_ref *ref) +{ + /* For now do not issue prefetches for only first few of the + iterations. */ + if (ref->prefetch_before != PREFETCH_ALL) + { + if (dump_file && (dump_flags & TDF_DETAILS)) + fprintf (dump_file, "Ignoring %p due to prefetch_before\n", + (void *) ref); + return false; + } + + /* Do not prefetch nontemporal stores. */ + if (ref->storent_p) + { + if (dump_file && (dump_flags & TDF_DETAILS)) + fprintf (dump_file, "Ignoring nontemporal store %p\n", (void *) ref); + return false; + } + + return true; +} + +/* Decide which of the prefetch candidates in GROUPS to prefetch. + AHEAD is the number of iterations to prefetch ahead (which corresponds + to the number of simultaneous instances of one prefetch running at a + time). UNROLL_FACTOR is the factor by that the loop is going to be + unrolled. Returns true if there is anything to prefetch. */ + +static bool +schedule_prefetches (struct mem_ref_group *groups, unsigned unroll_factor, + unsigned ahead) +{ + unsigned remaining_prefetch_slots, n_prefetches, prefetch_slots; + unsigned slots_per_prefetch; + struct mem_ref *ref; + bool any = false; + + /* At most SIMULTANEOUS_PREFETCHES should be running at the same time. */ + remaining_prefetch_slots = SIMULTANEOUS_PREFETCHES; + + /* The prefetch will run for AHEAD iterations of the original loop, i.e., + AHEAD / UNROLL_FACTOR iterations of the unrolled loop. In each iteration, + it will need a prefetch slot. */ + slots_per_prefetch = (ahead + unroll_factor / 2) / unroll_factor; + if (dump_file && (dump_flags & TDF_DETAILS)) + fprintf (dump_file, "Each prefetch instruction takes %u prefetch slots.\n", + slots_per_prefetch); + + /* For now we just take memory references one by one and issue + prefetches for as many as possible. The groups are sorted + starting with the largest step, since the references with + large step are more likely to cause many cache misses. */ + + for (; groups; groups = groups->next) + for (ref = groups->refs; ref; ref = ref->next) + { + if (!should_issue_prefetch_p (ref)) + continue; + + /* The loop is far from being sufficiently unrolled for this + prefetch. Do not generate prefetch to avoid many redudant + prefetches. */ + if (ref->prefetch_mod / unroll_factor > PREFETCH_MOD_TO_UNROLL_FACTOR_RATIO) + continue; + + /* If we need to prefetch the reference each PREFETCH_MOD iterations, + and we unroll the loop UNROLL_FACTOR times, we need to insert + ceil (UNROLL_FACTOR / PREFETCH_MOD) instructions in each + iteration. */ + n_prefetches = ((unroll_factor + ref->prefetch_mod - 1) + / ref->prefetch_mod); + prefetch_slots = n_prefetches * slots_per_prefetch; + + /* If more than half of the prefetches would be lost anyway, do not + issue the prefetch. */ + if (2 * remaining_prefetch_slots < prefetch_slots) + continue; + + ref->issue_prefetch_p = true; + + if (remaining_prefetch_slots <= prefetch_slots) + return true; + remaining_prefetch_slots -= prefetch_slots; + any = true; + } + + return any; +} + +/* Return TRUE if no prefetch is going to be generated in the given + GROUPS. */ + +static bool +nothing_to_prefetch_p (struct mem_ref_group *groups) +{ + struct mem_ref *ref; + + for (; groups; groups = groups->next) + for (ref = groups->refs; ref; ref = ref->next) + if (should_issue_prefetch_p (ref)) + return false; + + return true; +} + +/* Estimate the number of prefetches in the given GROUPS. + UNROLL_FACTOR is the factor by which LOOP was unrolled. */ + +static int +estimate_prefetch_count (struct mem_ref_group *groups, unsigned unroll_factor) +{ + struct mem_ref *ref; + unsigned n_prefetches; + int prefetch_count = 0; + + for (; groups; groups = groups->next) + for (ref = groups->refs; ref; ref = ref->next) + if (should_issue_prefetch_p (ref)) + { + n_prefetches = ((unroll_factor + ref->prefetch_mod - 1) + / ref->prefetch_mod); + prefetch_count += n_prefetches; + } + + return prefetch_count; +} + +/* Issue prefetches for the reference REF into loop as decided before. + HEAD is the number of iterations to prefetch ahead. UNROLL_FACTOR + is the factor by which LOOP was unrolled. */ + +static void +issue_prefetch_ref (struct mem_ref *ref, unsigned unroll_factor, unsigned ahead) +{ + HOST_WIDE_INT delta; + tree addr, addr_base, write_p, local, forward; + gimple prefetch; + gimple_stmt_iterator bsi; + unsigned n_prefetches, ap; + bool nontemporal = ref->reuse_distance >= L2_CACHE_SIZE_BYTES; + + if (dump_file && (dump_flags & TDF_DETAILS)) + fprintf (dump_file, "Issued%s prefetch for %p.\n", + nontemporal ? " nontemporal" : "", + (void *) ref); + + bsi = gsi_for_stmt (ref->stmt); + + n_prefetches = ((unroll_factor + ref->prefetch_mod - 1) + / ref->prefetch_mod); + addr_base = build_fold_addr_expr_with_type (ref->mem, ptr_type_node); + addr_base = force_gimple_operand_gsi (&bsi, unshare_expr (addr_base), + true, NULL, true, GSI_SAME_STMT); + write_p = ref->write_p ? integer_one_node : integer_zero_node; + local = nontemporal ? integer_zero_node : integer_three_node; + + for (ap = 0; ap < n_prefetches; ap++) + { + if (cst_and_fits_in_hwi (ref->group->step)) + { + /* Determine the address to prefetch. */ + delta = (ahead + ap * ref->prefetch_mod) * + int_cst_value (ref->group->step); + addr = fold_build_pointer_plus_hwi (addr_base, delta); + addr = force_gimple_operand_gsi (&bsi, unshare_expr (addr), true, NULL, + true, GSI_SAME_STMT); + } + else + { + /* The step size is non-constant but loop-invariant. We use the + heuristic to simply prefetch ahead iterations ahead. */ + forward = fold_build2 (MULT_EXPR, sizetype, + fold_convert (sizetype, ref->group->step), + fold_convert (sizetype, size_int (ahead))); + addr = fold_build_pointer_plus (addr_base, forward); + addr = force_gimple_operand_gsi (&bsi, unshare_expr (addr), true, + NULL, true, GSI_SAME_STMT); + } + /* Create the prefetch instruction. */ + prefetch = gimple_build_call (builtin_decl_explicit (BUILT_IN_PREFETCH), + 3, addr, write_p, local); + gsi_insert_before (&bsi, prefetch, GSI_SAME_STMT); + } +} + +/* Issue prefetches for the references in GROUPS into loop as decided before. + HEAD is the number of iterations to prefetch ahead. UNROLL_FACTOR is the + factor by that LOOP was unrolled. */ + +static void +issue_prefetches (struct mem_ref_group *groups, + unsigned unroll_factor, unsigned ahead) +{ + struct mem_ref *ref; + + for (; groups; groups = groups->next) + for (ref = groups->refs; ref; ref = ref->next) + if (ref->issue_prefetch_p) + issue_prefetch_ref (ref, unroll_factor, ahead); +} + +/* Returns true if REF is a memory write for that a nontemporal store insn + can be used. */ + +static bool +nontemporal_store_p (struct mem_ref *ref) +{ + enum machine_mode mode; + enum insn_code code; + + /* REF must be a write that is not reused. We require it to be independent + on all other memory references in the loop, as the nontemporal stores may + be reordered with respect to other memory references. */ + if (!ref->write_p + || !ref->independent_p + || ref->reuse_distance < L2_CACHE_SIZE_BYTES) + return false; + + /* Check that we have the storent instruction for the mode. */ + mode = TYPE_MODE (TREE_TYPE (ref->mem)); + if (mode == BLKmode) + return false; + + code = optab_handler (storent_optab, mode); + return code != CODE_FOR_nothing; +} + +/* If REF is a nontemporal store, we mark the corresponding modify statement + and return true. Otherwise, we return false. */ + +static bool +mark_nontemporal_store (struct mem_ref *ref) +{ + if (!nontemporal_store_p (ref)) + return false; + + if (dump_file && (dump_flags & TDF_DETAILS)) + fprintf (dump_file, "Marked reference %p as a nontemporal store.\n", + (void *) ref); + + gimple_assign_set_nontemporal_move (ref->stmt, true); + ref->storent_p = true; + + return true; +} + +/* Issue a memory fence instruction after LOOP. */ + +static void +emit_mfence_after_loop (struct loop *loop) +{ + VEC (edge, heap) *exits = get_loop_exit_edges (loop); + edge exit; + gimple call; + gimple_stmt_iterator bsi; + unsigned i; + + FOR_EACH_VEC_ELT (edge, exits, i, exit) + { + call = gimple_build_call (FENCE_FOLLOWING_MOVNT, 0); + + if (!single_pred_p (exit->dest) + /* If possible, we prefer not to insert the fence on other paths + in cfg. */ + && !(exit->flags & EDGE_ABNORMAL)) + split_loop_exit_edge (exit); + bsi = gsi_after_labels (exit->dest); + + gsi_insert_before (&bsi, call, GSI_NEW_STMT); + mark_virtual_ops_for_renaming (call); + } + + VEC_free (edge, heap, exits); + update_ssa (TODO_update_ssa_only_virtuals); +} + +/* Returns true if we can use storent in loop, false otherwise. */ + +static bool +may_use_storent_in_loop_p (struct loop *loop) +{ + bool ret = true; + + if (loop->inner != NULL) + return false; + + /* If we must issue a mfence insn after using storent, check that there + is a suitable place for it at each of the loop exits. */ + if (FENCE_FOLLOWING_MOVNT != NULL_TREE) + { + VEC (edge, heap) *exits = get_loop_exit_edges (loop); + unsigned i; + edge exit; + + FOR_EACH_VEC_ELT (edge, exits, i, exit) + if ((exit->flags & EDGE_ABNORMAL) + && exit->dest == EXIT_BLOCK_PTR) + ret = false; + + VEC_free (edge, heap, exits); + } + + return ret; +} + +/* Marks nontemporal stores in LOOP. GROUPS contains the description of memory + references in the loop. */ + +static void +mark_nontemporal_stores (struct loop *loop, struct mem_ref_group *groups) +{ + struct mem_ref *ref; + bool any = false; + + if (!may_use_storent_in_loop_p (loop)) + return; + + for (; groups; groups = groups->next) + for (ref = groups->refs; ref; ref = ref->next) + any |= mark_nontemporal_store (ref); + + if (any && FENCE_FOLLOWING_MOVNT != NULL_TREE) + emit_mfence_after_loop (loop); +} + +/* Determines whether we can profitably unroll LOOP FACTOR times, and if + this is the case, fill in DESC by the description of number of + iterations. */ + +static bool +should_unroll_loop_p (struct loop *loop, struct tree_niter_desc *desc, + unsigned factor) +{ + if (!can_unroll_loop_p (loop, factor, desc)) + return false; + + /* We only consider loops without control flow for unrolling. This is not + a hard restriction -- tree_unroll_loop works with arbitrary loops + as well; but the unrolling/prefetching is usually more profitable for + loops consisting of a single basic block, and we want to limit the + code growth. */ + if (loop->num_nodes > 2) + return false; + + return true; +} + +/* Determine the coefficient by that unroll LOOP, from the information + contained in the list of memory references REFS. Description of + umber of iterations of LOOP is stored to DESC. NINSNS is the number of + insns of the LOOP. EST_NITER is the estimated number of iterations of + the loop, or -1 if no estimate is available. */ + +static unsigned +determine_unroll_factor (struct loop *loop, struct mem_ref_group *refs, + unsigned ninsns, struct tree_niter_desc *desc, + HOST_WIDE_INT est_niter) +{ + unsigned upper_bound; + unsigned nfactor, factor, mod_constraint; + struct mem_ref_group *agp; + struct mem_ref *ref; + + /* First check whether the loop is not too large to unroll. We ignore + PARAM_MAX_UNROLL_TIMES, because for small loops, it prevented us + from unrolling them enough to make exactly one cache line covered by each + iteration. Also, the goal of PARAM_MAX_UNROLL_TIMES is to prevent + us from unrolling the loops too many times in cases where we only expect + gains from better scheduling and decreasing loop overhead, which is not + the case here. */ + upper_bound = PARAM_VALUE (PARAM_MAX_UNROLLED_INSNS) / ninsns; + + /* If we unrolled the loop more times than it iterates, the unrolled version + of the loop would be never entered. */ + if (est_niter >= 0 && est_niter < (HOST_WIDE_INT) upper_bound) + upper_bound = est_niter; + + if (upper_bound <= 1) + return 1; + + /* Choose the factor so that we may prefetch each cache just once, + but bound the unrolling by UPPER_BOUND. */ + factor = 1; + for (agp = refs; agp; agp = agp->next) + for (ref = agp->refs; ref; ref = ref->next) + if (should_issue_prefetch_p (ref)) + { + mod_constraint = ref->prefetch_mod; + nfactor = least_common_multiple (mod_constraint, factor); + if (nfactor <= upper_bound) + factor = nfactor; + } + + if (!should_unroll_loop_p (loop, desc, factor)) + return 1; + + return factor; +} + +/* Returns the total volume of the memory references REFS, taking into account + reuses in the innermost loop and cache line size. TODO -- we should also + take into account reuses across the iterations of the loops in the loop + nest. */ + +static unsigned +volume_of_references (struct mem_ref_group *refs) +{ + unsigned volume = 0; + struct mem_ref_group *gr; + struct mem_ref *ref; + + for (gr = refs; gr; gr = gr->next) + for (ref = gr->refs; ref; ref = ref->next) + { + /* Almost always reuses another value? */ + if (ref->prefetch_before != PREFETCH_ALL) + continue; + + /* If several iterations access the same cache line, use the size of + the line divided by this number. Otherwise, a cache line is + accessed in each iteration. TODO -- in the latter case, we should + take the size of the reference into account, rounding it up on cache + line size multiple. */ + volume += L1_CACHE_LINE_SIZE / ref->prefetch_mod; + } + return volume; +} + +/* Returns the volume of memory references accessed across VEC iterations of + loops, whose sizes are described in the LOOP_SIZES array. N is the number + of the loops in the nest (length of VEC and LOOP_SIZES vectors). */ + +static unsigned +volume_of_dist_vector (lambda_vector vec, unsigned *loop_sizes, unsigned n) +{ + unsigned i; + + for (i = 0; i < n; i++) + if (vec[i] != 0) + break; + + if (i == n) + return 0; + + gcc_assert (vec[i] > 0); + + /* We ignore the parts of the distance vector in subloops, since usually + the numbers of iterations are much smaller. */ + return loop_sizes[i] * vec[i]; +} + +/* Add the steps of ACCESS_FN multiplied by STRIDE to the array STRIDE + at the position corresponding to the loop of the step. N is the depth + of the considered loop nest, and, LOOP is its innermost loop. */ + +static void +add_subscript_strides (tree access_fn, unsigned stride, + HOST_WIDE_INT *strides, unsigned n, struct loop *loop) +{ + struct loop *aloop; + tree step; + HOST_WIDE_INT astep; + unsigned min_depth = loop_depth (loop) - n; + + while (TREE_CODE (access_fn) == POLYNOMIAL_CHREC) + { + aloop = get_chrec_loop (access_fn); + step = CHREC_RIGHT (access_fn); + access_fn = CHREC_LEFT (access_fn); + + if ((unsigned) loop_depth (aloop) <= min_depth) + continue; + + if (host_integerp (step, 0)) + astep = tree_low_cst (step, 0); + else + astep = L1_CACHE_LINE_SIZE; + + strides[n - 1 - loop_depth (loop) + loop_depth (aloop)] += astep * stride; + + } +} + +/* Returns the volume of memory references accessed between two consecutive + self-reuses of the reference DR. We consider the subscripts of DR in N + loops, and LOOP_SIZES contains the volumes of accesses in each of the + loops. LOOP is the innermost loop of the current loop nest. */ + +static unsigned +self_reuse_distance (data_reference_p dr, unsigned *loop_sizes, unsigned n, + struct loop *loop) +{ + tree stride, access_fn; + HOST_WIDE_INT *strides, astride; + VEC (tree, heap) *access_fns; + tree ref = DR_REF (dr); + unsigned i, ret = ~0u; + + /* In the following example: + + for (i = 0; i < N; i++) + for (j = 0; j < N; j++) + use (a[j][i]); + the same cache line is accessed each N steps (except if the change from + i to i + 1 crosses the boundary of the cache line). Thus, for self-reuse, + we cannot rely purely on the results of the data dependence analysis. + + Instead, we compute the stride of the reference in each loop, and consider + the innermost loop in that the stride is less than cache size. */ + + strides = XCNEWVEC (HOST_WIDE_INT, n); + access_fns = DR_ACCESS_FNS (dr); + + FOR_EACH_VEC_ELT (tree, access_fns, i, access_fn) + { + /* Keep track of the reference corresponding to the subscript, so that we + know its stride. */ + while (handled_component_p (ref) && TREE_CODE (ref) != ARRAY_REF) + ref = TREE_OPERAND (ref, 0); + + if (TREE_CODE (ref) == ARRAY_REF) + { + stride = TYPE_SIZE_UNIT (TREE_TYPE (ref)); + if (host_integerp (stride, 1)) + astride = tree_low_cst (stride, 1); + else + astride = L1_CACHE_LINE_SIZE; + + ref = TREE_OPERAND (ref, 0); + } + else + astride = 1; + + add_subscript_strides (access_fn, astride, strides, n, loop); + } + + for (i = n; i-- > 0; ) + { + unsigned HOST_WIDE_INT s; + + s = strides[i] < 0 ? -strides[i] : strides[i]; + + if (s < (unsigned) L1_CACHE_LINE_SIZE + && (loop_sizes[i] + > (unsigned) (L1_CACHE_SIZE_BYTES / NONTEMPORAL_FRACTION))) + { + ret = loop_sizes[i]; + break; + } + } + + free (strides); + return ret; +} + +/* Determines the distance till the first reuse of each reference in REFS + in the loop nest of LOOP. NO_OTHER_REFS is true if there are no other + memory references in the loop. */ + +static void +determine_loop_nest_reuse (struct loop *loop, struct mem_ref_group *refs, + bool no_other_refs) +{ + struct loop *nest, *aloop; + VEC (data_reference_p, heap) *datarefs = NULL; + VEC (ddr_p, heap) *dependences = NULL; + struct mem_ref_group *gr; + struct mem_ref *ref, *refb; + VEC (loop_p, heap) *vloops = NULL; + unsigned *loop_data_size; + unsigned i, j, n; + unsigned volume, dist, adist; + HOST_WIDE_INT vol; + data_reference_p dr; + ddr_p dep; + + if (loop->inner) + return; + + /* Find the outermost loop of the loop nest of loop (we require that + there are no sibling loops inside the nest). */ + nest = loop; + while (1) + { + aloop = loop_outer (nest); + + if (aloop == current_loops->tree_root + || aloop->inner->next) + break; + + nest = aloop; + } + + /* For each loop, determine the amount of data accessed in each iteration. + We use this to estimate whether the reference is evicted from the + cache before its reuse. */ + find_loop_nest (nest, &vloops); + n = VEC_length (loop_p, vloops); + loop_data_size = XNEWVEC (unsigned, n); + volume = volume_of_references (refs); + i = n; + while (i-- != 0) + { + loop_data_size[i] = volume; + /* Bound the volume by the L2 cache size, since above this bound, + all dependence distances are equivalent. */ + if (volume > L2_CACHE_SIZE_BYTES) + continue; + + aloop = VEC_index (loop_p, vloops, i); + vol = max_stmt_executions_int (aloop, false); + if (vol < 0) + vol = expected_loop_iterations (aloop); + volume *= vol; + } + + /* Prepare the references in the form suitable for data dependence + analysis. We ignore unanalyzable data references (the results + are used just as a heuristics to estimate temporality of the + references, hence we do not need to worry about correctness). */ + for (gr = refs; gr; gr = gr->next) + for (ref = gr->refs; ref; ref = ref->next) + { + dr = create_data_ref (nest, loop_containing_stmt (ref->stmt), + ref->mem, ref->stmt, !ref->write_p); + + if (dr) + { + ref->reuse_distance = volume; + dr->aux = ref; + VEC_safe_push (data_reference_p, heap, datarefs, dr); + } + else + no_other_refs = false; + } + + FOR_EACH_VEC_ELT (data_reference_p, datarefs, i, dr) + { + dist = self_reuse_distance (dr, loop_data_size, n, loop); + ref = (struct mem_ref *) dr->aux; + if (ref->reuse_distance > dist) + ref->reuse_distance = dist; + + if (no_other_refs) + ref->independent_p = true; + } + + compute_all_dependences (datarefs, &dependences, vloops, true); + + FOR_EACH_VEC_ELT (ddr_p, dependences, i, dep) + { + if (DDR_ARE_DEPENDENT (dep) == chrec_known) + continue; + + ref = (struct mem_ref *) DDR_A (dep)->aux; + refb = (struct mem_ref *) DDR_B (dep)->aux; + + if (DDR_ARE_DEPENDENT (dep) == chrec_dont_know + || DDR_NUM_DIST_VECTS (dep) == 0) + { + /* If the dependence cannot be analyzed, assume that there might be + a reuse. */ + dist = 0; + + ref->independent_p = false; + refb->independent_p = false; + } + else + { + /* The distance vectors are normalized to be always lexicographically + positive, hence we cannot tell just from them whether DDR_A comes + before DDR_B or vice versa. However, it is not important, + anyway -- if DDR_A is close to DDR_B, then it is either reused in + DDR_B (and it is not nontemporal), or it reuses the value of DDR_B + in cache (and marking it as nontemporal would not affect + anything). */ + + dist = volume; + for (j = 0; j < DDR_NUM_DIST_VECTS (dep); j++) + { + adist = volume_of_dist_vector (DDR_DIST_VECT (dep, j), + loop_data_size, n); + + /* If this is a dependence in the innermost loop (i.e., the + distances in all superloops are zero) and it is not + the trivial self-dependence with distance zero, record that + the references are not completely independent. */ + if (lambda_vector_zerop (DDR_DIST_VECT (dep, j), n - 1) + && (ref != refb + || DDR_DIST_VECT (dep, j)[n-1] != 0)) + { + ref->independent_p = false; + refb->independent_p = false; + } + + /* Ignore accesses closer than + L1_CACHE_SIZE_BYTES / NONTEMPORAL_FRACTION, + so that we use nontemporal prefetches e.g. if single memory + location is accessed several times in a single iteration of + the loop. */ + if (adist < L1_CACHE_SIZE_BYTES / NONTEMPORAL_FRACTION) + continue; + + if (adist < dist) + dist = adist; + } + } + + if (ref->reuse_distance > dist) + ref->reuse_distance = dist; + if (refb->reuse_distance > dist) + refb->reuse_distance = dist; + } + + free_dependence_relations (dependences); + free_data_refs (datarefs); + free (loop_data_size); + + if (dump_file && (dump_flags & TDF_DETAILS)) + { + fprintf (dump_file, "Reuse distances:\n"); + for (gr = refs; gr; gr = gr->next) + for (ref = gr->refs; ref; ref = ref->next) + fprintf (dump_file, " ref %p distance %u\n", + (void *) ref, ref->reuse_distance); + } +} + +/* Determine whether or not the trip count to ahead ratio is too small based + on prefitablility consideration. + AHEAD: the iteration ahead distance, + EST_NITER: the estimated trip count. */ + +static bool +trip_count_to_ahead_ratio_too_small_p (unsigned ahead, HOST_WIDE_INT est_niter) +{ + /* Assume trip count to ahead ratio is big enough if the trip count could not + be estimated at compile time. */ + if (est_niter < 0) + return false; + + if (est_niter < (HOST_WIDE_INT) (TRIP_COUNT_TO_AHEAD_RATIO * ahead)) + { + if (dump_file && (dump_flags & TDF_DETAILS)) + fprintf (dump_file, + "Not prefetching -- loop estimated to roll only %d times\n", + (int) est_niter); + return true; + } + + return false; +} + +/* Determine whether or not the number of memory references in the loop is + reasonable based on the profitablity and compilation time considerations. + NINSNS: estimated number of instructions in the loop, + MEM_REF_COUNT: total number of memory references in the loop. */ + +static bool +mem_ref_count_reasonable_p (unsigned ninsns, unsigned mem_ref_count) +{ + int insn_to_mem_ratio; + + if (mem_ref_count == 0) + return false; + + /* Miss rate computation (is_miss_rate_acceptable) and dependence analysis + (compute_all_dependences) have high costs based on quadratic complexity. + To avoid huge compilation time, we give up prefetching if mem_ref_count + is too large. */ + if (mem_ref_count > PREFETCH_MAX_MEM_REFS_PER_LOOP) + return false; + + /* Prefetching improves performance by overlapping cache missing + memory accesses with CPU operations. If the loop does not have + enough CPU operations to overlap with memory operations, prefetching + won't give a significant benefit. One approximate way of checking + this is to require the ratio of instructions to memory references to + be above a certain limit. This approximation works well in practice. + TODO: Implement a more precise computation by estimating the time + for each CPU or memory op in the loop. Time estimates for memory ops + should account for cache misses. */ + insn_to_mem_ratio = ninsns / mem_ref_count; + + if (insn_to_mem_ratio < PREFETCH_MIN_INSN_TO_MEM_RATIO) + { + if (dump_file && (dump_flags & TDF_DETAILS)) + fprintf (dump_file, + "Not prefetching -- instruction to memory reference ratio (%d) too small\n", + insn_to_mem_ratio); + return false; + } + + return true; +} + +/* Determine whether or not the instruction to prefetch ratio in the loop is + too small based on the profitablity consideration. + NINSNS: estimated number of instructions in the loop, + PREFETCH_COUNT: an estimate of the number of prefetches, + UNROLL_FACTOR: the factor to unroll the loop if prefetching. */ + +static bool +insn_to_prefetch_ratio_too_small_p (unsigned ninsns, unsigned prefetch_count, + unsigned unroll_factor) +{ + int insn_to_prefetch_ratio; + + /* Prefetching most likely causes performance degradation when the instruction + to prefetch ratio is too small. Too many prefetch instructions in a loop + may reduce the I-cache performance. + (unroll_factor * ninsns) is used to estimate the number of instructions in + the unrolled loop. This implementation is a bit simplistic -- the number + of issued prefetch instructions is also affected by unrolling. So, + prefetch_mod and the unroll factor should be taken into account when + determining prefetch_count. Also, the number of insns of the unrolled + loop will usually be significantly smaller than the number of insns of the + original loop * unroll_factor (at least the induction variable increases + and the exit branches will get eliminated), so it might be better to use + tree_estimate_loop_size + estimated_unrolled_size. */ + insn_to_prefetch_ratio = (unroll_factor * ninsns) / prefetch_count; + if (insn_to_prefetch_ratio < MIN_INSN_TO_PREFETCH_RATIO) + { + if (dump_file && (dump_flags & TDF_DETAILS)) + fprintf (dump_file, + "Not prefetching -- instruction to prefetch ratio (%d) too small\n", + insn_to_prefetch_ratio); + return true; + } + + return false; +} + + +/* Issue prefetch instructions for array references in LOOP. Returns + true if the LOOP was unrolled. */ + +static bool +loop_prefetch_arrays (struct loop *loop) +{ + struct mem_ref_group *refs; + unsigned ahead, ninsns, time, unroll_factor; + HOST_WIDE_INT est_niter; + struct tree_niter_desc desc; + bool unrolled = false, no_other_refs; + unsigned prefetch_count; + unsigned mem_ref_count; + + if (optimize_loop_nest_for_size_p (loop)) + { + if (dump_file && (dump_flags & TDF_DETAILS)) + fprintf (dump_file, " ignored (cold area)\n"); + return false; + } + + /* FIXME: the time should be weighted by the probabilities of the blocks in + the loop body. */ + time = tree_num_loop_insns (loop, &eni_time_weights); + if (time == 0) + return false; + + ahead = (PREFETCH_LATENCY + time - 1) / time; + est_niter = max_stmt_executions_int (loop, false); + + /* Prefetching is not likely to be profitable if the trip count to ahead + ratio is too small. */ + if (trip_count_to_ahead_ratio_too_small_p (ahead, est_niter)) + return false; + + ninsns = tree_num_loop_insns (loop, &eni_size_weights); + + /* Step 1: gather the memory references. */ + refs = gather_memory_references (loop, &no_other_refs, &mem_ref_count); + + /* Give up prefetching if the number of memory references in the + loop is not reasonable based on profitablity and compilation time + considerations. */ + if (!mem_ref_count_reasonable_p (ninsns, mem_ref_count)) + goto fail; + + /* Step 2: estimate the reuse effects. */ + prune_by_reuse (refs); + + if (nothing_to_prefetch_p (refs)) + goto fail; + + determine_loop_nest_reuse (loop, refs, no_other_refs); + + /* Step 3: determine unroll factor. */ + unroll_factor = determine_unroll_factor (loop, refs, ninsns, &desc, + est_niter); + + /* Estimate prefetch count for the unrolled loop. */ + prefetch_count = estimate_prefetch_count (refs, unroll_factor); + if (prefetch_count == 0) + goto fail; + + if (dump_file && (dump_flags & TDF_DETAILS)) + fprintf (dump_file, "Ahead %d, unroll factor %d, trip count " + HOST_WIDE_INT_PRINT_DEC "\n" + "insn count %d, mem ref count %d, prefetch count %d\n", + ahead, unroll_factor, est_niter, + ninsns, mem_ref_count, prefetch_count); + + /* Prefetching is not likely to be profitable if the instruction to prefetch + ratio is too small. */ + if (insn_to_prefetch_ratio_too_small_p (ninsns, prefetch_count, + unroll_factor)) + goto fail; + + mark_nontemporal_stores (loop, refs); + + /* Step 4: what to prefetch? */ + if (!schedule_prefetches (refs, unroll_factor, ahead)) + goto fail; + + /* Step 5: unroll the loop. TODO -- peeling of first and last few + iterations so that we do not issue superfluous prefetches. */ + if (unroll_factor != 1) + { + tree_unroll_loop (loop, unroll_factor, + single_dom_exit (loop), &desc); + unrolled = true; + } + + /* Step 6: issue the prefetches. */ + issue_prefetches (refs, unroll_factor, ahead); + +fail: + release_mem_refs (refs); + return unrolled; +} + +/* Issue prefetch instructions for array references in loops. */ + +unsigned int +tree_ssa_prefetch_arrays (void) +{ + loop_iterator li; + struct loop *loop; + bool unrolled = false; + int todo_flags = 0; + + if (!HAVE_prefetch + /* It is possible to ask compiler for say -mtune=i486 -march=pentium4. + -mtune=i486 causes us having PREFETCH_BLOCK 0, since this is part + of processor costs and i486 does not have prefetch, but + -march=pentium4 causes HAVE_prefetch to be true. Ugh. */ + || PREFETCH_BLOCK == 0) + return 0; + + if (dump_file && (dump_flags & TDF_DETAILS)) + { + fprintf (dump_file, "Prefetching parameters:\n"); + fprintf (dump_file, " simultaneous prefetches: %d\n", + SIMULTANEOUS_PREFETCHES); + fprintf (dump_file, " prefetch latency: %d\n", PREFETCH_LATENCY); + fprintf (dump_file, " prefetch block size: %d\n", PREFETCH_BLOCK); + fprintf (dump_file, " L1 cache size: %d lines, %d kB\n", + L1_CACHE_SIZE_BYTES / L1_CACHE_LINE_SIZE, L1_CACHE_SIZE); + fprintf (dump_file, " L1 cache line size: %d\n", L1_CACHE_LINE_SIZE); + fprintf (dump_file, " L2 cache size: %d kB\n", L2_CACHE_SIZE); + fprintf (dump_file, " min insn-to-prefetch ratio: %d \n", + MIN_INSN_TO_PREFETCH_RATIO); + fprintf (dump_file, " min insn-to-mem ratio: %d \n", + PREFETCH_MIN_INSN_TO_MEM_RATIO); + fprintf (dump_file, "\n"); + } + + initialize_original_copy_tables (); + + if (!builtin_decl_explicit_p (BUILT_IN_PREFETCH)) + { + tree type = build_function_type_list (void_type_node, + const_ptr_type_node, NULL_TREE); + tree decl = add_builtin_function ("__builtin_prefetch", type, + BUILT_IN_PREFETCH, BUILT_IN_NORMAL, + NULL, NULL_TREE); + DECL_IS_NOVOPS (decl) = true; + set_builtin_decl (BUILT_IN_PREFETCH, decl, false); + } + + /* We assume that size of cache line is a power of two, so verify this + here. */ + gcc_assert ((PREFETCH_BLOCK & (PREFETCH_BLOCK - 1)) == 0); + + FOR_EACH_LOOP (li, loop, LI_FROM_INNERMOST) + { + if (dump_file && (dump_flags & TDF_DETAILS)) + fprintf (dump_file, "Processing loop %d:\n", loop->num); + + unrolled |= loop_prefetch_arrays (loop); + + if (dump_file && (dump_flags & TDF_DETAILS)) + fprintf (dump_file, "\n\n"); + } + + if (unrolled) + { + scev_reset (); + todo_flags |= TODO_cleanup_cfg; + } + + free_original_copy_tables (); + return todo_flags; +} -- cgit v1.2.3