[clang] [CIR] Fold load from constant alloca slots (PR #212284)

[Erich Keane via cfe-commits]

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@@ -32,6 +33,68 @@ namespace mlir {
 
 namespace {
 
+/// Find the `cir.store` operation that stores to the given alloca and dominates
+/// the given load operation. Dominance calculation is done through the given
+/// DominanceInfo object.
+///
+/// Return nullptr if no such store operation exists. If multiple store
+/// operations satisfy the criteria, any of them may be returned.
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erichkeane wrote:

Folks do 'weird' stuff with const :D  Casting it away is actually pretty common and doesn't fall in UB under at least some uses.

IF it is too much trouble to find the 'most recent' one (I was hoping there was some level of 'just search backwards' here...) I think skipping out if we find a 2nd one is a good idea.

https://github.com/llvm/llvm-project/pull/212284