[llvm] [SME] Stop RA from coalescing COPY instructions that transcend beyond smstart/smstop. (PR #78294)

[Amara Emerson via llvm-commits]

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@@ -8063,7 +8079,8 @@ AArch64TargetLowering::LowerCall(CallLoweringInfo &CLI,
   // return.
   SDValue Result = LowerCallResult(Chain, InGlue, CallConv, IsVarArg, RVLocs,
                                    DL, DAG, InVals, IsThisReturn,
-                                   IsThisReturn ? OutVals[0] : SDValue());
+                                   IsThisReturn ? OutVals[0] : SDValue(),
+                                   RequiresSMChange.has_value());
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aemerson wrote:

RequiresSMChange being an `optional<bool>` is unclear to me what it means, and why having any value at all is what you want for the value of LowerCallResult()'s `bool RequiresSMChange` parameter.

https://github.com/llvm/llvm-project/pull/78294