[llvm] AMDGPU: Perform zero/any extend combine into permute (PR #177370)

[via llvm-commits]

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@@ -14470,7 +14473,43 @@ SDValue SITargetLowering::performZeroExtendCombine(SDNode *N,
   if (Src.getValueType() != MVT::i16)
     return SDValue();
 
-  return SDValue();
+  if (!Src->hasOneUse())
+    return SDValue();
+
+  // TODO: We bail out below if SrcOffset is not in the first dword (>= 4). It's
+  // possible we're missing out on some combine opportunities, but we'd need to
+  // weigh the cost of extracting the byte from the upper dwords.
+
+  std::optional<ByteProvider<SDValue>> BP0 =
+      calculateByteProvider(SDValue(N, 0), 0, 0, 0);
+  if (!BP0 || BP0->SrcOffset >= 4 || !BP0->Src)
+    return SDValue();
+  SDValue V0 = *BP0->Src;
+
+  std::optional<ByteProvider<SDValue>> BP1 =
+      calculateByteProvider(SDValue(N, 0), 1, 0, 1);
+  if (!BP1 || BP1->SrcOffset >= 4 || !BP1->Src)
+    return SDValue();
+  SDValue V1 = *BP1->Src;
+
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macurtis-amd wrote:

I added a blank like above the assignment. Hopefully that's what you wanted.

https://github.com/llvm/llvm-project/pull/177370