Deoptimization-based bce.

A mechanism is introduced that a runtime method can be called
from code compiled with optimizing compiler to deoptimize into
interpreter. This can be used to establish invariants in the managed code
If the invariant does not hold at runtime, we will deoptimize and continue
execution in the interpreter. This allows to optimize the managed code as
if the invariant was proven during compile time. However, the exception
will be thrown according to the semantics demanded by the spec.

The invariant and optimization included in this patch are based on the
length of an array. Given a set of array accesses with constant indices
{c1, ..., cn}, we can optimize away all bounds checks iff all 0 <= min(ci) and
max(ci) < array-length. The first can be proven statically. The second can be
established with a deoptimization-based invariant. This replaces n bounds
checks with one invariant check (plus slow-path code).

Change-Id: I8c6e34b56c85d25b91074832d13dba1db0a81569

1 files changed, 74 insertions, 22 deletions

diff --git a/compiler/optimizing/code_generator_arm.cc b/compiler/optimizing/code_generator_arm.cc
index 0a069a75ef..363fbeffb6 100644
--- a/compiler/optimizing/code_generator_arm.cc
+++ b/compiler/optimizing/code_generator_arm.cc
@@ -305,6 +305,26 @@ class TypeCheckSlowPathARM : public SlowPathCodeARM {
   DISALLOW_COPY_AND_ASSIGN(TypeCheckSlowPathARM);
 };
 
+class DeoptimizationSlowPathARM : public SlowPathCodeARM {
+ public:
+  explicit DeoptimizationSlowPathARM(HInstruction* instruction)
+    : instruction_(instruction) {}
+
+  void EmitNativeCode(CodeGenerator* codegen) OVERRIDE {
+    __ Bind(GetEntryLabel());
+    SaveLiveRegisters(codegen, instruction_->GetLocations());
+    DCHECK(instruction_->IsDeoptimize());
+    HDeoptimize* deoptimize = instruction_->AsDeoptimize();
+    uint32_t dex_pc = deoptimize->GetDexPc();
+    CodeGeneratorARM* arm_codegen = down_cast<CodeGeneratorARM*>(codegen);
+    arm_codegen->InvokeRuntime(QUICK_ENTRY_POINT(pDeoptimize), instruction_, dex_pc, this);
+  }
+
+ private:
+  HInstruction* const instruction_;
+  DISALLOW_COPY_AND_ASSIGN(DeoptimizationSlowPathARM);
+};
+
 #undef __
 
 #undef __
@@ -905,24 +925,17 @@ void InstructionCodeGeneratorARM::VisitExit(HExit* exit) {
   UNUSED(exit);
 }
 
-void LocationsBuilderARM::VisitIf(HIf* if_instr) {
-  LocationSummary* locations =
-      new (GetGraph()->GetArena()) LocationSummary(if_instr, LocationSummary::kNoCall);
-  HInstruction* cond = if_instr->InputAt(0);
-  if (!cond->IsCondition() || cond->AsCondition()->NeedsMaterialization()) {
-    locations->SetInAt(0, Location::RequiresRegister());
-  }
-}
-
-void InstructionCodeGeneratorARM::VisitIf(HIf* if_instr) {
-  HInstruction* cond = if_instr->InputAt(0);
+void InstructionCodeGeneratorARM::GenerateTestAndBranch(HInstruction* instruction,
+                                                        Label* true_target,
+                                                        Label* false_target,
+                                                        Label* always_true_target) {
+  HInstruction* cond = instruction->InputAt(0);
   if (cond->IsIntConstant()) {
     // Constant condition, statically compared against 1.
     int32_t cond_value = cond->AsIntConstant()->GetValue();
     if (cond_value == 1) {
-      if (!codegen_->GoesToNextBlock(if_instr->GetBlock(),
-                                     if_instr->IfTrueSuccessor())) {
-        __ b(codegen_->GetLabelOf(if_instr->IfTrueSuccessor()));
+      if (always_true_target != nullptr) {
+        __ b(always_true_target);
       }
       return;
     } else {
@@ -931,10 +944,10 @@ void InstructionCodeGeneratorARM::VisitIf(HIf* if_instr) {
   } else {
     if (!cond->IsCondition() || cond->AsCondition()->NeedsMaterialization()) {
       // Condition has been materialized, compare the output to 0
-      DCHECK(if_instr->GetLocations()->InAt(0).IsRegister());
-      __ cmp(if_instr->GetLocations()->InAt(0).AsRegister<Register>(),
+      DCHECK(instruction->GetLocations()->InAt(0).IsRegister());
+      __ cmp(instruction->GetLocations()->InAt(0).AsRegister<Register>(),
              ShifterOperand(0));
-      __ b(codegen_->GetLabelOf(if_instr->IfTrueSuccessor()), NE);
+      __ b(true_target, NE);
     } else {
       // Condition has not been materialized, use its inputs as the
       // comparison and its condition as the branch condition.
@@ -956,16 +969,55 @@ void InstructionCodeGeneratorARM::VisitIf(HIf* if_instr) {
           __ cmp(left, ShifterOperand(temp));
         }
       }
-      __ b(codegen_->GetLabelOf(if_instr->IfTrueSuccessor()),
-           ARMCondition(cond->AsCondition()->GetCondition()));
+      __ b(true_target);
     }
   }
-  if (!codegen_->GoesToNextBlock(if_instr->GetBlock(),
-                                 if_instr->IfFalseSuccessor())) {
-    __ b(codegen_->GetLabelOf(if_instr->IfFalseSuccessor()));
+  if (false_target != nullptr) {
+    __ b(false_target);
   }
 }
 
+void LocationsBuilderARM::VisitIf(HIf* if_instr) {
+  LocationSummary* locations =
+      new (GetGraph()->GetArena()) LocationSummary(if_instr, LocationSummary::kNoCall);
+  HInstruction* cond = if_instr->InputAt(0);
+  if (!cond->IsCondition() || cond->AsCondition()->NeedsMaterialization()) {
+    locations->SetInAt(0, Location::RequiresRegister());
+  }
+}
+
+void InstructionCodeGeneratorARM::VisitIf(HIf* if_instr) {
+  Label* true_target = codegen_->GetLabelOf(if_instr->IfTrueSuccessor());
+  Label* false_target = codegen_->GetLabelOf(if_instr->IfFalseSuccessor());
+  Label* always_true_target = true_target;
+  if (codegen_->GoesToNextBlock(if_instr->GetBlock(),
+                                if_instr->IfTrueSuccessor())) {
+    always_true_target = nullptr;
+  }
+  if (codegen_->GoesToNextBlock(if_instr->GetBlock(),
+                                if_instr->IfFalseSuccessor())) {
+    false_target = nullptr;
+  }
+  GenerateTestAndBranch(if_instr, true_target, false_target, always_true_target);
+}
+
+void LocationsBuilderARM::VisitDeoptimize(HDeoptimize* deoptimize) {
+  LocationSummary* locations = new (GetGraph()->GetArena())
+      LocationSummary(deoptimize, LocationSummary::kCallOnSlowPath);
+  HInstruction* cond = deoptimize->InputAt(0);
+  DCHECK(cond->IsCondition());
+  if (cond->AsCondition()->NeedsMaterialization()) {
+    locations->SetInAt(0, Location::RequiresRegister());
+  }
+}
+
+void InstructionCodeGeneratorARM::VisitDeoptimize(HDeoptimize* deoptimize) {
+  SlowPathCodeARM* slow_path = new (GetGraph()->GetArena())
+      DeoptimizationSlowPathARM(deoptimize);
+  codegen_->AddSlowPath(slow_path);
+  Label* slow_path_entry = slow_path->GetEntryLabel();
+  GenerateTestAndBranch(deoptimize, slow_path_entry, nullptr, slow_path_entry);
+}
 
 void LocationsBuilderARM::VisitCondition(HCondition* comp) {
   LocationSummary* locations =