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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@113640 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/llvm/Target/TargetInstrInfo.h b/include/llvm/Target/TargetInstrInfo.h
index 844b96566a3d2965afad2e50fca5c6fff56af3df..f4652011e92cf31901383a38ca2813553ff2a813 100644 (file)
--- a/include/llvm/Target/TargetInstrInfo.h
+++ b/include/llvm/Target/TargetInstrInfo.h
@@ -586,9 +586,11 @@ 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 {
+  /// that we can remove a "comparison with zero".  Update the iterator *only*
+  /// if a transformation took place.
+  virtual bool ConvertToSetZeroFlag(MachineInstr * /*Instr*/,
+                                    MachineInstr * /*CmpInstr*/,
+                                    MachineBasicBlock::iterator &) const {
     return false;
   }
 

diff --git a/lib/CodeGen/PeepholeOptimizer.cpp b/lib/CodeGen/PeepholeOptimizer.cpp
index ea14d276d5b1769bd12c90ac277408c29cf47589..a4ff04bec1ceba4d3f07f1eb46622a6edfd7bb6e 100644 (file)
--- a/lib/CodeGen/PeepholeOptimizer.cpp
+++ b/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/lib/Target/ARM/ARMBaseInstrInfo.cpp b/lib/Target/ARM/ARMBaseInstrInfo.cpp
index e7024d6da716b5e206355258d9a0fb811d8ab5a1..142633c667fac61a1ef694b3c117cb0205460c03 100644 (file)
--- a/lib/Target/ARM/ARMBaseInstrInfo.cpp
+++ b/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/lib/Target/ARM/ARMBaseInstrInfo.h b/lib/Target/ARM/ARMBaseInstrInfo.h
index f471b6772e77330b9b0d52910ef6ee62cf81c13b..622402eba35342aa86518b1ac41eb5f991980c2c 100644 (file)
--- a/lib/Target/ARM/ARMBaseInstrInfo.h
+++ b/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;