[llvm-bugs] [Bug 43507] New: v8i1 build_vector legalizer miscompile

via llvm-bugs llvm-bugs at lists.llvm.org
Mon Sep 30 08:42:37 PDT 2019


            Bug ID: 43507
           Summary: v8i1 build_vector legalizer miscompile
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Backend: X86
          Assignee: unassignedbugs at nondot.org
          Reporter: benny.kra at gmail.com
                CC: craig.topper at gmail.com, llvm-bugs at lists.llvm.org,
                    llvm-dev at redking.me.uk, spatel+llvm at rotateright.com

$ cat t.ll
define <8 x i1> @ham(i64 %arg) {
  %tmp = trunc i64 %arg to i1
  %tmp1 = insertelement <8 x i1> undef, i1 %tmp, i32 0
  %tmp2 = shufflevector <8 x i1> %tmp1, <8 x i1> undef, <8 x i32>
  ret <8 x i1> %tmp2

$ llc -mcpu=skx < t.ll
        xorl    %eax, %eax
        testb   %dil, %dil
        movl    $255, %ecx
        cmovel  %eax, %ecx
        kmovd   %ecx, %k0
        vpmovm2w        %k0, %xmm0

This drops the trunc to i1, giving wrong results for all even inputs > 0. I'd
expect `testb $1, %dil` here.

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