[llvm] [AArch64][SME] Add remarks to flag lazy ZA saves, and SMSTART/SMSTOP transitions (PR #68255)

[Jon Roelofs via llvm-commits]

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@@ -7362,6 +7363,18 @@ AArch64TargetLowering::LowerCall(CallLoweringInfo &CLI,
   else if (auto *ES = dyn_cast<ExternalSymbolSDNode>(CLI.Callee))
     CalleeAttrs = SMEAttrs(ES->getSymbol());
 
+  auto DescribeCallsite =
+      [&](OptimizationRemarkAnalysis &R) -> OptimizationRemarkAnalysis & {
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jroelofs wrote:

I was thinking the current format would be a bit nicer for additions, i.e. if/when ZA liveness starts being tracked, the remark could be amended to mention the number of za slices that should be preserved.

https://github.com/llvm/llvm-project/pull/68255