[PATCH] D124530: [X86] Fix gather/scatter with large scales (PR55021)

[Pei, Gen via Phabricator via llvm-commits]

gpei added inline comments.


================
Comment at: llvm/lib/Target/X86/X86ISelLowering.cpp:31567
+    EVT IndexVT = Index.getValueType();
+    Index = DAG.getNode(ISD::SHL, dl, IndexVT, Index,
+                        DAG.getConstant(Log2_32(ScaleVal), dl, IndexVT));
----------------
```
DATA_ADDR←BASE_ADDR + (SignExtend(VINDEX[i+31:i])*SCALE + DISP;
```

Gather will signextend(index) to 64-bit first, then multiple the scale. When Index is 32-bit, it may occur overflow if we just multiply scale to index.

BTW, can we just bail out in getUniformBase when the scale is not supported by the target.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D124530/new/

https://reviews.llvm.org/D124530