[llvm] [InstCombine] fold `select (trunc nuw X to i1), X, Y` to `select (trunc nuw X to i1), 1, Y` (PR #105914)

[Nikita Popov via llvm-commits]

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@@ -4201,5 +4201,15 @@ Instruction *InstCombinerImpl::visitSelectInst(SelectInst &SI) {
     }
   }
 
+  // select (trunc nuw X to i1), X, Y --> select (trunc nuw X to i1), 1, Y
+  if (auto *TI = dyn_cast<TruncInst>(CondVal)) {
+    Value *Trunc;
+    if (TI->hasNoUnsignedWrap() && match(CondVal, m_Trunc(m_Value(Trunc))) &&
+        match(TrueVal, m_Specific(Trunc))) {
+      return SelectInst::Create(
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nikic wrote:

Use replaceOperand() instead, to preserve select metadata.

https://github.com/llvm/llvm-project/pull/105914