[PATCH] D46957: [x86] Lower some trunc + shuffle patterns to vpmov[q|d][b|w]

[Gabor Buella via Phabricator via llvm-commits]

GBuella added inline comments.


================
Comment at: lib/Target/X86/X86ISelLowering.cpp:9429
+  while (I < Size) {
+    if (isInRange(Mask[I], TruncatedVectorStart, TruncatedVectorStart + Size))
+      return false;
----------------
RKSimon wrote:
> GBuella wrote:
> > RKSimon wrote:
> > > Why can't you permit UNDEFs in the shuffle mask?
> > I do permit undef here. The condition of the branch is what I don't permit.
> Then why don't you use isUndefOrZeroOrInRange()?
> ```
> if (!isUndefOrZeroOrInRange(Mask.slice(Split, Size), TruncatedVectorStart, TruncatedVectorStart + Size))
>   return false;
> ```
That would check for the wrong elements, wouldn't it?
Maybe 
```
OtherVectorStart = SwappedOps ? 0 : Size
if (!isUndefOrZeroOrInRange(Mask.slice(Split, Size), OtherVectorStart, OtherVectorStart + Size))
  return false;
```



https://reviews.llvm.org/D46957