[LLVMbugs] [Bug 17654] New: [AVX] scalarized code generated for zext of <16 x i8> to <16 x i16>

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=17654

            Bug ID: 17654
           Summary: [AVX] scalarized code generated for zext of <16 x i8>
                    to <16 x i16>
           Product: new-bugs
           Version: unspecified
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: matt at pharr.org
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

With top of tree and "llc -mattr=+avx", this code

define <16 x i16> @bar(<16 x i8> %v) {
  %v16 = zext <16 x i8> %v to <16 x i16>
  ret <16 x i16> %v16
}

generates a long sequence of vpextrb/vpinsrw instructions.

However, if I manually break the vector into two <8 x i8> vectors, do two
zexts, and then reassemble the 16-wide vector, like this:

define <16 x i16> @bat(<16 x i8> %v) {
  %va = shufflevector <16 x i8> %v, <16 x i8> undef, <8 x i32> <i32 0, i32 1,
i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
  %vb = shufflevector <16 x i8> %v, <16 x i8> undef, <8 x i32> <i32 8, i32 9,
i32 10, i32 11, i32 12, i32 13, i32 14, i32 15>
  %va16 = zext <8 x i8> %va to <8 x i16>
  %vb16 = zext <8 x i8> %vb to <8 x i16>
  %v16 = shufflevector <8 x i16> %va16, <8 x i16> %vb16,
             <16 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32
7,
                         i32 8, i32 9, i32 10, i32 11, i32 12, i32 13, i32 14,
i32 15>
  ret <16 x i16> %v16
}

then I get the nice output:

        vpunpckhbw      %xmm0, %xmm0, %xmm1 # xmm1 =
xmm0[8,8,9,9,10,10,11,11,12,12,13,13,14,14,15,15]
        vmovdqa .LCPI2_0(%rip), %xmm2
        vpand   %xmm2, %xmm1, %xmm1
        vpmovzxbw       %xmm0, %xmm0
        vpand   %xmm2, %xmm0, %xmm0
        vinsertf128     $1, %xmm1, %ymm0, %ymm0

It'd be nice if the first implementation got this output as well.

-- 
You are receiving this mail because:
You are on the CC list for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-bugs/attachments/20131022/b9e77def/attachment.html>