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>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@163535 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 29 insertions, 2 deletions

diff --git a/lib/Target/ARM/ARMBaseInstrInfo.cpp b/lib/Target/ARM/ARMBaseInstrInfo.cpp
index 10c41ee..e2f0d7d 100644
--- a/lib/Target/ARM/ARMBaseInstrInfo.cpp
+++ b/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.
diff --git a/test/CodeGen/ARM/sub-cmp-peephole.ll b/test/CodeGen/ARM/sub-cmp-peephole.ll
index 6fcbdee..2961b94 100644
--- a/test/CodeGen/ARM/sub-cmp-peephole.ll
+++ b/test/CodeGen/ARM/sub-cmp-peephole.ll
@@ -63,3 +63,24 @@ if.then:
 if.else:
   ret i32 %sub
 }
+
+; If the sub/rsb instruction is predicated, we can't use the flags.
+; <rdar://problem/12263428>
+; Test case from MultiSource/Benchmarks/Ptrdist/bc/number.s
+; CHECK: bc_raise
+; CHECK: rsbeq
+; CHECK: cmp
+define i32 @bc_raise() nounwind ssp {
+entry:
+  %val.2.i = select i1 undef, i32 0, i32 undef
+  %sub.i = sub nsw i32 0, %val.2.i
+  %retval.0.i = select i1 undef, i32 %val.2.i, i32 %sub.i
+  %cmp1 = icmp eq i32 %retval.0.i, 0
+  br i1 %cmp1, label %land.lhs.true, label %if.end11
+
+land.lhs.true:                                    ; preds = %num2long.exit
+  ret i32 17
+
+if.end11:                                         ; preds = %num2long.exit
+  ret i32 23
+}