[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:

Do we perhaps want the 'last' use?  I guess the hope is that because it is a 'constant' that we would only have a single 'store' though, right?  Coudl we potentially have a:

alloca
store to it
store to it
load

Where we replace it with the 1st 'store to it'?  (perhaps with some scopes in the way?).  Why isn't that a problem? 

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