[llvm] [Remarks] Emit SROA and mem2reg missed remarks (PR #221094)

[Eli Friedman via llvm-commits]

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@@ -6159,6 +6179,24 @@ bool SROA::propagateStoredValuesToLoads(AllocaInst &AI, AllocaSlices &AS) {
   return true;
 }
 
+/// Report an aggregate allocation that slice analysis could not take apart.
+/// Only aggregates are reported: an escaping scalar alloca is not a missed
+/// splitting opportunity. The remark is anchored at the blocking use rather
+/// than the alloca, because that use is what the user can act on.
+static void reportAllocaNotSplit(const AllocaInst &AI, const AllocaSlices &AS,
+                                 OptimizationRemarkEmitter *ORE) {
+  if (!ORE || !AI.getAllocatedType()->isAggregateType())
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efriedma-quic wrote:

This doesn't match how SROA actually works... whether we can split is mostly independent of the result of getAllocatedType().

https://github.com/llvm/llvm-project/pull/221094