[cfe-dev] OpenCL shift on short/char types

[Pete Couperus]

Hello,

OpenCL defines shifts so the requested shift size is masked.
I'm looking at the IR generated by clang for shifts in OpenCL, and had a question.
For int shifts, clang creates a mask and does the shift on the mask of the requested shift, like so:
  %shr.mask = and i32 %b, 31
  %shr = lshr i32 %a, %shr.mask
This is basically what I would expect.

For shifts on shorts/chars:
uchar
s(uchar a, uchar b) {
  return a >> b;
}

Clang generates:
define zeroext i8 @s(i8 zeroext %a, i8 zeroext %b) #0 {
entry:
  %conv = zext i8 %a to i32
  %conv1 = zext i8 %b to i32
  %shr.mask = and i32 %conv1, 31
  %shr = lshr i32 %conv, %shr.mask
  %conv2 = trunc i32 %shr to i8
  ret i8 %conv2
}

I expected the mask in this case to be done "and 7" rather than "and 31".
Is this a bug in clang, or is my expectation/understanding wrong?
Thanks!

Pete

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