[InstCombine] Negate ABS/NABS patterns by swapping the select operands to remove the negation
Differential Revision: https://reviews.llvm.org/D47236
llvm-svn: 333101
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index 0df56bd..1e4c38c 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1628,6 +1628,22 @@
Value *ShAmtOp = cast<Instruction>(Op1)->getOperand(1);
return BinaryOperator::CreateLShr(X, ShAmtOp);
}
+
+ if (Op1->hasOneUse()) {
+ Value *LHS, *RHS;
+ SelectPatternFlavor SPF = matchSelectPattern(Op1, LHS, RHS).Flavor;
+ if (SPF == SPF_ABS || SPF == SPF_NABS) {
+ // This is a negate of an ABS/NABS pattern. Just swap the operands
+ // of the select.
+ SelectInst *SI = cast<SelectInst>(Op1);
+ Value *TrueVal = SI->getTrueValue();
+ Value *FalseVal = SI->getFalseValue();
+ SI->setTrueValue(FalseVal);
+ SI->setFalseValue(TrueVal);
+ // Don't swap prof metadata, we didn't change the branch behavior.
+ return replaceInstUsesWith(I, SI);
+ }
+ }
}
// Turn this into a xor if LHS is 2^n-1 and the remaining bits are known