[PATCH] D45572: [X86] Replace action Promote with Custom for operation ISD::SINT_TO_FP

[Craig Topper via Phabricator via llvm-commits]

craig.topper added inline comments.


================
Comment at: lib/Target/X86/X86ISelLowering.cpp:238
     setOperationAction(ISD::SINT_TO_FP     , MVT::i16  , Promote);
-    setOperationAction(ISD::SINT_TO_FP     , MVT::i32  , Promote);
+    setOperationAction(ISD::SINT_TO_FP     , MVT::i32  , Custom);
   }
----------------
efriedma wrote:
> Normally, you'd use "Expand" to indicate this is always a libcall.
I think really the problem is that UINT_TO_FP is defaulting to Legal in this case. So this DAG combine is being allowed to fire. Making SINT_TO_FP Custom stops this, but I think you really want to set UINT_TO_FP to Promote. Or maybe set them both to Expand as Eli suggested. It doesn't necessarily matter because we should be softening the float before we get to legalize ops.

```
  // If the input is a legal type, and SINT_TO_FP is not legal on this target,
  // but UINT_TO_FP is legal on this target, try to convert.
  if (!TLI.isOperationLegalOrCustom(ISD::SINT_TO_FP, OpVT) &&
      TLI.isOperationLegalOrCustom(ISD::UINT_TO_FP, OpVT)) {
    // If the sign bit is known to be zero, we can change this to UINT_TO_FP.
    if (DAG.SignBitIsZero(N0))
      return DAG.getNode(ISD::UINT_TO_FP, SDLoc(N), VT, N0);
  }
```


Repository:
  rL LLVM

https://reviews.llvm.org/D45572