Run codegen dce pass for all targets at all optimization levels. Previously it's

only run for x86 with fastisel. I've found it being very effective in
eliminating some obvious dead code as result of formal parameter lowering
especially when tail call optimization eliminated the need for some of the loads
from fixed frame objects. It also shrinks a number of the tests. A couple of
tests no longer make sense and are now eliminated.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@95493 91177308-0d34-0410-b5e6-96231b3b80d8

4 files changed, 14 insertions, 4 deletions

diff --git a/lib/CodeGen/DeadMachineInstructionElim.cpp b/lib/CodeGen/DeadMachineInstructionElim.cpp
index 9d7ec06ac9..a0544d07ba 100644
--- a/lib/CodeGen/DeadMachineInstructionElim.cpp
+++ b/lib/CodeGen/DeadMachineInstructionElim.cpp
@@ -11,6 +11,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+#define DEBUG_TYPE "codegen-dce"
 #include "llvm/CodeGen/Passes.h"
 #include "llvm/Pass.h"
 #include "llvm/CodeGen/MachineFunctionPass.h"
@@ -19,8 +20,11 @@
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Target/TargetInstrInfo.h"
 #include "llvm/Target/TargetMachine.h"
+#include "llvm/ADT/Statistic.h"
 using namespace llvm;
 
+STATISTIC(NumDeletes,          "Number of dead instructions deleted");
+
 namespace {
   class DeadMachineInstructionElim : public MachineFunctionPass {
     virtual bool runOnMachineFunction(MachineFunction &MF);
@@ -126,6 +130,7 @@ bool DeadMachineInstructionElim::runOnMachineFunction(MachineFunction &MF) {
         DEBUG(dbgs() << "DeadMachineInstructionElim: DELETING: " << *MI);
         AnyChanges = true;
         MI->eraseFromParent();
+        ++NumDeletes;
         MIE = MBB->rend();
         // MII is now pointing to the next instruction to process,
         // so don't increment it.
diff --git a/lib/CodeGen/LLVMTargetMachine.cpp b/lib/CodeGen/LLVMTargetMachine.cpp
index c03e4290ca..40e015067f 100644
--- a/lib/CodeGen/LLVMTargetMachine.cpp
+++ b/lib/CodeGen/LLVMTargetMachine.cpp
@@ -291,6 +291,12 @@ bool LLVMTargetMachine::addCommonCodeGenPasses(PassManagerBase &PM,
   printAndVerify(PM, "After Instruction Selection",
                  /* allowDoubleDefs= */ true);
 
+
+  // Delete dead machine instructions regardless of optimization level.
+  PM.add(createDeadMachineInstructionElimPass());
+  printAndVerify(PM, "After codegen DCE pass",
+                 /* allowDoubleDefs= */ true);
+
   if (OptLevel != CodeGenOpt::None) {
     PM.add(createOptimizeExtsPass());
     if (!DisableMachineLICM)
diff --git a/lib/CodeGen/LiveIntervalAnalysis.cpp b/lib/CodeGen/LiveIntervalAnalysis.cpp
index 8746bf9086..c52156ad20 100644
--- a/lib/CodeGen/LiveIntervalAnalysis.cpp
+++ b/lib/CodeGen/LiveIntervalAnalysis.cpp
@@ -671,6 +671,9 @@ void LiveIntervals::computeIntervals() {
   for (MachineFunction::iterator MBBI = mf_->begin(), E = mf_->end();
        MBBI != E; ++MBBI) {
     MachineBasicBlock *MBB = MBBI;
+    if (MBB->empty())
+      continue;
+
     // Track the index of the current machine instr.
     SlotIndex MIIndex = getMBBStartIdx(MBB);
     DEBUG(dbgs() << MBB->getName() << ":\n");
diff --git a/lib/Target/X86/X86TargetMachine.cpp b/lib/Target/X86/X86TargetMachine.cpp
index 2e7febcdbb..f835e295e6 100644
--- a/lib/Target/X86/X86TargetMachine.cpp
+++ b/lib/Target/X86/X86TargetMachine.cpp
@@ -148,10 +148,6 @@ bool X86TargetMachine::addInstSelector(PassManagerBase &PM,
   // Install an instruction selector.
   PM.add(createX86ISelDag(*this, OptLevel));
 
-  // If we're using Fast-ISel, clean up the mess.
-  if (EnableFastISel)
-    PM.add(createDeadMachineInstructionElimPass());
-
   // Install a pass to insert x87 FP_REG_KILL instructions, as needed.
   PM.add(createX87FPRegKillInserterPass());