[ValueTracking] Look through casts when both operands are casts.
We only looked through casts when one operand was a constant. We can also look through casts when both operands are non-constant, but both are in fact the same cast type. For example:
%1 = icmp ult i8 %a, %b
%2 = zext i8 %a to i32
%3 = zext i8 %b to i32
%4 = select i1 %1, i32 %2, i32 %3
llvm-svn: 246678
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 352b0fb..7de7195 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -3750,14 +3750,26 @@
return {SPF_UNKNOWN, SPNB_NA, false};
}
-static Constant *lookThroughCast(CmpInst *CmpI, Value *V1, Value *V2,
- Instruction::CastOps *CastOp) {
+static Value *lookThroughCast(CmpInst *CmpI, Value *V1, Value *V2,
+ Instruction::CastOps *CastOp) {
CastInst *CI = dyn_cast<CastInst>(V1);
Constant *C = dyn_cast<Constant>(V2);
- if (!CI || !C)
+ CastInst *CI2 = dyn_cast<CastInst>(V2);
+ if (!CI)
return nullptr;
*CastOp = CI->getOpcode();
+ if (CI2) {
+ // If V1 and V2 are both the same cast from the same type, we can look
+ // through V1.
+ if (CI2->getOpcode() == CI->getOpcode() &&
+ CI2->getSrcTy() == CI->getSrcTy())
+ return CI2->getOperand(0);
+ return nullptr;
+ } else if (!C) {
+ return nullptr;
+ }
+
if (isa<SExtInst>(CI) && CmpI->isSigned()) {
Constant *T = ConstantExpr::getTrunc(C, CI->getSrcTy());
// This is only valid if the truncated value can be sign-extended
@@ -3817,11 +3829,11 @@
// Deal with type mismatches.
if (CastOp && CmpLHS->getType() != TrueVal->getType()) {
- if (Constant *C = lookThroughCast(CmpI, TrueVal, FalseVal, CastOp))
+ if (Value *C = lookThroughCast(CmpI, TrueVal, FalseVal, CastOp))
return ::matchSelectPattern(Pred, FMF, CmpLHS, CmpRHS,
cast<CastInst>(TrueVal)->getOperand(0), C,
LHS, RHS);
- if (Constant *C = lookThroughCast(CmpI, FalseVal, TrueVal, CastOp))
+ if (Value *C = lookThroughCast(CmpI, FalseVal, TrueVal, CastOp))
return ::matchSelectPattern(Pred, FMF, CmpLHS, CmpRHS,
C, cast<CastInst>(FalseVal)->getOperand(0),
LHS, RHS);