Don't attempt to use flags from predicated instructions.

The ARM backend can eliminate cmp instructions by reusing flags from a
nearby sub instruction with similar arguments.

Don't do that if the sub is predicated - the flags are not written
unconditionally.

<rdar://problem/12263428>

llvm-svn: 163535

1 files changed, 8 insertions, 2 deletions

diff --git a/llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp b/llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp
index 10c41ee6c49..e2f0d7d4bdf 100644
--- a/llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp
+++ b/llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp
@@ -2028,13 +2028,14 @@ optimizeCompareInstr(MachineInstr *CmpInstr, unsigned SrcReg, unsigned SrcReg2,
 
   // Masked compares sometimes use the same register as the corresponding 'and'.
   if (CmpMask != ~0) {
-    if (!isSuitableForMask(MI, SrcReg, CmpMask, false)) {
+    if (!isSuitableForMask(MI, SrcReg, CmpMask, false) || isPredicated(MI)) {
       MI = 0;
       for (MachineRegisterInfo::use_iterator UI = MRI->use_begin(SrcReg),
            UE = MRI->use_end(); UI != UE; ++UI) {
         if (UI->getParent() != CmpInstr->getParent()) continue;
         MachineInstr *PotentialAND = &*UI;
-        if (!isSuitableForMask(PotentialAND, SrcReg, CmpMask, true))
+        if (!isSuitableForMask(PotentialAND, SrcReg, CmpMask, true) ||
+            isPredicated(PotentialAND))
           continue;
         MI = PotentialAND;
         break;
@@ -2100,6 +2101,10 @@ optimizeCompareInstr(MachineInstr *CmpInstr, unsigned SrcReg, unsigned SrcReg2,
   // The single candidate is called MI.
   if (!MI) MI = Sub;
 
+  // We can't use a predicated instruction - it doesn't always write the flags.
+  if (isPredicated(MI))
+    return false;
+
   switch (MI->getOpcode()) {
   default: break;
   case ARM::RSBrr:
@@ -2206,6 +2211,7 @@ optimizeCompareInstr(MachineInstr *CmpInstr, unsigned SrcReg, unsigned SrcReg2,
     // Toggle the optional operand to CPSR.
     MI->getOperand(5).setReg(ARM::CPSR);
     MI->getOperand(5).setIsDef(true);
+    assert(!isPredicated(MI) && "Can't use flags from predicated instruction");
     CmpInstr->eraseFromParent();
 
     // Modify the condition code of operands in OperandsToUpdate.