Reapply r88830 with a bugfix: this transform only applies to icmp eq/ne. This
fixes part of PR5438.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@89639 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index 6f74902..99555ea 100644
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -8539,6 +8539,36 @@
}
}
+ // icmp ne A, B is equal to xor A, B when A and B only really have one bit.
+ // It is also profitable to transform icmp eq into not(xor(A, B)) because that
+ // may lead to additional simplifications.
+ if (ICI->isEquality() && CI.getType() == ICI->getOperand(0)->getType()) {
+ if (const IntegerType *ITy = dyn_cast<IntegerType>(CI.getType())) {
+ uint32_t BitWidth = ITy->getBitWidth();
+ if (BitWidth > 1) {
+ Value *LHS = ICI->getOperand(0);
+ Value *RHS = ICI->getOperand(1);
+
+ APInt KnownZeroLHS(BitWidth, 0), KnownOneLHS(BitWidth, 0);
+ APInt KnownZeroRHS(BitWidth, 0), KnownOneRHS(BitWidth, 0);
+ APInt TypeMask(APInt::getHighBitsSet(BitWidth, BitWidth-1));
+ ComputeMaskedBits(LHS, TypeMask, KnownZeroLHS, KnownOneLHS);
+ ComputeMaskedBits(RHS, TypeMask, KnownZeroRHS, KnownOneRHS);
+
+ if (KnownZeroLHS.countLeadingOnes() == BitWidth-1 &&
+ KnownZeroRHS.countLeadingOnes() == BitWidth-1) {
+ if (!DoXform) return ICI;
+
+ Value *Xor = Builder->CreateXor(LHS, RHS);
+ if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
+ Xor = Builder->CreateXor(Xor, ConstantInt::get(ITy, 1));
+ Xor->takeName(ICI);
+ return ReplaceInstUsesWith(CI, Xor);
+ }
+ }
+ }
+ }
+
return 0;
}