Modify the comparison optimizations in the peephole optimizer to update the

iterator when an optimization took place. This allows us to do more insane
things with the code than just remove an instruction or two.

llvm-svn: 113640

3 files changed, 17 insertions, 9 deletions

diff --git a/llvm/lib/CodeGen/PeepholeOptimizer.cpp b/llvm/lib/CodeGen/PeepholeOptimizer.cpp
index ea14d276d5b..a4ff04bec1c 100644
--- a/llvm/lib/CodeGen/PeepholeOptimizer.cpp
+++ b/llvm/lib/CodeGen/PeepholeOptimizer.cpp
@@ -76,7 +76,8 @@ namespace {
     }
 
   private:
-    bool OptimizeCmpInstr(MachineInstr *MI, MachineBasicBlock *MBB);
+    bool OptimizeCmpInstr(MachineInstr *MI, MachineBasicBlock *MBB,
+                          MachineBasicBlock::iterator &MII);
     bool OptimizeExtInstr(MachineInstr *MI, MachineBasicBlock *MBB,
                           SmallPtrSet<MachineInstr*, 8> &LocalMIs);
   };
@@ -232,7 +233,8 @@ OptimizeExtInstr(MachineInstr *MI, MachineBasicBlock *MBB,
 /// set) the same flag as the compare, then we can remove the comparison and use
 /// the flag from the previous instruction.
 bool PeepholeOptimizer::OptimizeCmpInstr(MachineInstr *MI,
-                                         MachineBasicBlock *MBB) {
+                                         MachineBasicBlock *MBB,
+                                         MachineBasicBlock::iterator &NextIter){
   // If this instruction is a comparison against zero and isn't comparing a
   // physical register, we can try to optimize it.
   unsigned SrcReg;
@@ -247,7 +249,7 @@ bool PeepholeOptimizer::OptimizeCmpInstr(MachineInstr *MI,
     return false;
 
   // Attempt to convert the defining instruction to set the "zero" flag.
-  if (TII->ConvertToSetZeroFlag(&*DI, MI)) {
+  if (TII->ConvertToSetZeroFlag(&*DI, MI, NextIter)) {
     ++NumEliminated;
     return true;
   }
@@ -269,12 +271,14 @@ bool PeepholeOptimizer::runOnMachineFunction(MachineFunction &MF) {
     LocalMIs.clear();
 
     for (MachineBasicBlock::iterator
-           MII = I->begin(), ME = I->end(); MII != ME; ) {
+           MII = I->begin(), MIE = I->end(); MII != MIE; ) {
       MachineInstr *MI = &*MII;
 
       if (MI->getDesc().isCompare()) {
-        ++MII; // The iterator may become invalid if the compare is deleted.
-        Changed |= OptimizeCmpInstr(MI, MBB);
+        if (OptimizeCmpInstr(MI, MBB, MII))
+          Changed = true;
+        else
+          ++MII;
       } else {
         Changed |= OptimizeExtInstr(MI, MBB, LocalMIs);
         ++MII;
diff --git a/llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp b/llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp
index e7024d6da71..142633c667f 100644
--- a/llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp
+++ b/llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp
@@ -1378,9 +1378,11 @@ AnalyzeCompare(const MachineInstr *MI, unsigned &SrcReg, int &CmpValue) const {
 }
 
 /// ConvertToSetZeroFlag - Convert the instruction to set the "zero" flag so
-/// that we can remove a "comparison with zero".
+/// that we can remove a "comparison with zero". Update the iterator *only* if a
+/// transformation took place.
 bool ARMBaseInstrInfo::
-ConvertToSetZeroFlag(MachineInstr *MI, MachineInstr *CmpInstr) const {
+ConvertToSetZeroFlag(MachineInstr *MI, MachineInstr *CmpInstr,
+                     MachineBasicBlock::iterator &MII) const {
   // Conservatively refuse to convert an instruction which isn't in the same BB
   // as the comparison.
   if (MI->getParent() != CmpInstr->getParent())
@@ -1414,6 +1416,7 @@ ConvertToSetZeroFlag(MachineInstr *MI, MachineInstr *CmpInstr) const {
     MI->RemoveOperand(5);
     MachineInstrBuilder(MI)
       .addReg(ARM::CPSR, RegState::Define | RegState::Implicit);
+    MII = llvm::next(MachineBasicBlock::iterator(CmpInstr));
     CmpInstr->eraseFromParent();
     return true;
   }
diff --git a/llvm/lib/Target/ARM/ARMBaseInstrInfo.h b/llvm/lib/Target/ARM/ARMBaseInstrInfo.h
index f471b6772e7..622402eba35 100644
--- a/llvm/lib/Target/ARM/ARMBaseInstrInfo.h
+++ b/llvm/lib/Target/ARM/ARMBaseInstrInfo.h
@@ -347,7 +347,8 @@ public:
   /// ConvertToSetZeroFlag - Convert the instruction to set the zero flag so
   /// that we can remove a "comparison with zero".
   virtual bool ConvertToSetZeroFlag(MachineInstr *Instr,
-                                    MachineInstr *CmpInstr) const;
+                                    MachineInstr *CmpInstr,
+                                    MachineBasicBlock::iterator &MII) const;
 
   virtual unsigned getNumMicroOps(const MachineInstr *MI,
                                   const InstrItineraryData *ItinData) const;