From ea5c6be76664e91d8da69efb2dfc0038e93a76e4 Mon Sep 17 00:00:00 2001
From: Evan Cheng <evan.cheng@apple.com>
Date: Sat, 6 Feb 2010 09:07:11 +0000
Subject: 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.

llvm-svn: 95493
---
 llvm/lib/CodeGen/DeadMachineInstructionElim.cpp | 5 +++++
 llvm/lib/CodeGen/LLVMTargetMachine.cpp          | 6 ++++++
 llvm/lib/CodeGen/LiveIntervalAnalysis.cpp       | 3 +++
 3 files changed, 14 insertions(+)

(limited to 'llvm/lib/CodeGen')

diff --git a/llvm/lib/CodeGen/DeadMachineInstructionElim.cpp b/llvm/lib/CodeGen/DeadMachineInstructionElim.cpp
index 9d7ec06ac97..a0544d07bab 100644
--- a/llvm/lib/CodeGen/DeadMachineInstructionElim.cpp
+++ b/llvm/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/llvm/lib/CodeGen/LLVMTargetMachine.cpp b/llvm/lib/CodeGen/LLVMTargetMachine.cpp
index c03e4290cab..40e015067f4 100644
--- a/llvm/lib/CodeGen/LLVMTargetMachine.cpp
+++ b/llvm/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/llvm/lib/CodeGen/LiveIntervalAnalysis.cpp b/llvm/lib/CodeGen/LiveIntervalAnalysis.cpp
index 8746bf90865..c52156ad207 100644
--- a/llvm/lib/CodeGen/LiveIntervalAnalysis.cpp
+++ b/llvm/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");
-- 
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