[llvm] [InstCombine] Fold `mul (sext bool X), Y` into `select X, -Y, 0` (PR #84792)

[Yingwei Zheng via llvm-commits]

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@@ -448,6 +448,20 @@ Instruction *InstCombinerImpl::visitMul(BinaryOperator &I) {
   if (match(Op1, m_ZExt(m_Value(X))) && X->getType()->isIntOrIntVectorTy(1))
     return SelectInst::Create(X, Op0, ConstantInt::getNullValue(Ty));
 
+  // mul (sext X), Y -> select X, -Y, 0
+  // mul Y, (sext X) -> select X, -Y, 0
+  Value *SExtOp;
+  if (match(Op0, m_OneUse(m_SExt(m_Value(SExtOp)))) &&
+      SExtOp->getType()->isIntOrIntVectorTy(1)) {
+    return SelectInst::Create(SExtOp, Builder.CreateNeg(Op1),
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dtcxzyw wrote:

We can propagate the nsw flag to neg: https://alive2.llvm.org/ce/z/AOU8xE.


https://github.com/llvm/llvm-project/pull/84792