[PATCH] D56987: [Intrinsic] Expand SMULFIX to MUL, MULH[US], or [US]MUL_LOHI on vector arguments

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon added inline comments.


================
Comment at: llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp:5367
+  // [us]mul.fix(a, b, 0) -> mul(a, b)
+  if (!Scale && isOperationLegalOrCustom(ISD::MUL, VT))
+    return DAG.getNode(ISD::MUL, dl, VT, LHS, RHS);
----------------
Doesn't this have to be:
```
if (!Scale) {
  if(VT.isVector() && !isOperationLegalOrCustom(ISD::MUL, VT)))
    return SDValue();
  return DAG.getNode(ISD::MUL, dl, VT, LHS, RHS);
} 
```
otherwise scale == 0 cases can fall through and cause undef for out of range shifts.


Repository:
  rL LLVM

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D56987/new/

https://reviews.llvm.org/D56987