[llvm] [InstCombine] Enable select freeze poison folding when storing value (PR #129776)

[John McIver via llvm-commits]

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@@ -4812,7 +4812,14 @@ Instruction *InstCombinerImpl::visitFreeze(FreezeInst &I) {
   //
   // TODO: This could use getBinopAbsorber() / getBinopIdentity() to avoid
   //       duplicating logic for binops at least.
-  auto getUndefReplacement = [&I](Type *Ty) {
+  auto getUndefReplacement = [&I, &AC = this->AC,
+                              &DT = this->DT](Type *Ty) -> Value * {
+    Value *SelectArgument = nullptr;
+    if (match(&I, m_OneUse(m_Freeze(m_Poison()))) &&
+        match(I.user_back(),
+              m_c_Select(m_Specific(&I), m_Value(SelectArgument))) &&
+        isGuaranteedNotToBeUndefOrPoison(SelectArgument, &AC, &I, &DT))
+      return SelectArgument;
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jmciver wrote:

The transformation was based on a single use of freeze poison so we hoisted it out of the use analysis loop.

To verify we would want to be able to do something like the following?
https://alive2.llvm.org/ce/z/pyGVuw

https://github.com/llvm/llvm-project/pull/129776