[llvm] [DAGCombiner][AMDGPU] Track signedness in ByteProviders (PR #65995)

[Jeffrey Byrnes via llvm-commits]

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@@ -10558,11 +10562,15 @@ calculateSrcByte(const SDValue Op, uint64_t DestByte, uint64_t SrcIndex = 0,
 
     SrcIndex += BitShift / 8;
 
-    return calculateSrcByte(Op->getOperand(0), DestByte, SrcIndex, Depth + 1);
+    return calculateSrcByte(Op->getOperand(0), DestByte, SrcIndex, IsSigned,
+                            Depth + 1);
   }
 
   default: {
-    return ByteProvider<SDValue>::getSrc(Op, DestByte, SrcIndex);
+    if (auto L = dyn_cast<LoadSDNode>(Op))
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jrbyrnes wrote:

I'm not convinced we should be combining atomics to begin with.

I've blacklisted atomics / memtrinsic until we have a better idea of how to handle the signedness of such. Primarily `isMemIntrinsic` will need to be handled as these should be supported ByteProviders.

https://github.com/llvm/llvm-project/pull/65995