Provide an option to restore old-style if-conversion heuristics for Thumb2.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@115339 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/ARM/Thumb2InstrInfo.cpp

@@ -28,6 +28,11 @@
 
 using namespace llvm;
 
+static cl::opt<bool>
+OldT2IfCvt("old-thumb2-ifcvt", cl::Hidden,
+           cl::desc("Use old-style Thumb2 if-conversion heuristics"),
+           cl::init(false));
+
 Thumb2InstrInfo::Thumb2InstrInfo(const ARMSubtarget &STI)
   : ARMBaseInstrInfo(STI), RI(*this, STI) {
 }
@@ -37,6 +42,30 @@ unsigned Thumb2InstrInfo::getUnindexedOpcode(unsigned Opc) const {
   return 0;
 }
 
+bool Thumb2InstrInfo::isProfitableToIfCvt(MachineBasicBlock &MBB,
+                                          unsigned NumInstrs,
+                                          float Prediction) const {
+  if (!OldT2IfCvt)
+    return ARMBaseInstrInfo::isProfitableToIfCvt(MBB, NumInstrs, Prediction);
+  return NumInstrs && NumInstrs <= 3;
+}
+  
+bool Thumb2InstrInfo::
+isProfitableToIfCvt(MachineBasicBlock &TMBB, unsigned NumT,
+                    MachineBasicBlock &FMBB, unsigned NumF,
+                    float Prediction) const {
+  if (!OldT2IfCvt)
+    return ARMBaseInstrInfo::isProfitableToIfCvt(TMBB, NumT,
+                                                 FMBB, NumF, Prediction);
+    
+  // FIXME: Catch optimization such as:
+  //        r0 = movne
+  //        r0 = moveq
+  return NumT && NumF &&
+    NumT <= 3 && NumF <= 3;
+}
+
+
 void
 Thumb2InstrInfo::ReplaceTailWithBranchTo(MachineBasicBlock::iterator Tail,
                                          MachineBasicBlock *NewDest) const {

lib/Target/ARM/Thumb2InstrInfo.h

@@ -38,6 +38,12 @@ public:
   bool isLegalToSplitMBBAt(MachineBasicBlock &MBB,
                            MachineBasicBlock::iterator MBBI) const;
 
+  bool isProfitableToIfCvt(MachineBasicBlock &MBB, unsigned NumInstrs,
+                           float Prediction) const;
+  bool isProfitableToIfCvt(MachineBasicBlock &TMBB, unsigned NumTInstrs,
+                           MachineBasicBlock &FMBB, unsigned NumFInstrs,
+                           float Prediction) const;
+
   void copyPhysReg(MachineBasicBlock &MBB,
                    MachineBasicBlock::iterator I, DebugLoc DL,
                    unsigned DestReg, unsigned SrcReg,