[llvm] [AMDGPU] Fix LDS access via flat pointer argument in amdgpu-sw-lower-lds (PR #209842)

[Shilei Tian via llvm-commits]

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@@ -287,6 +303,99 @@ void AMDGPUSwLowerLDS::getNonKernelsWithLDSArguments(const CallGraph &CG) {
   }
 }
 
+// True if flat pointer V is derived from an LDS-carrying argument in LDSArgs,
+// looking through GEP/bitcast/phi/select; Visited breaks phi cycles. When
+// AcceptLocalCast is set, a flat<-local addrspacecast also counts as an origin.
+// Detection (getNonKernelsWithLDSFlatArguments) sets it, since that cast is how
+// LDS first enters a flat pointer; the rewrite
+// (getFlatPtrForRoundTripLDSAccess) leaves it clear so only argument origins
+// qualify.
+static bool flatPtrDerivesFromLDS(Value *V,
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shiltian wrote:

Function should start with a verb.

https://github.com/llvm/llvm-project/pull/209842