[llvm-bugs] [Bug 34047] New: Extra bitcasts prevent simplification of bit select

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=34047

            Bug ID: 34047
           Summary: Extra bitcasts prevent simplification of bit select
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Common Code Generator Code
          Assignee: unassignedbugs at nondot.org
          Reporter: llvm-dev at redking.me.uk
                CC: llvm-bugs at lists.llvm.org, spatel+llvm at rotateright.com

Two versions of the same 'select based on comparison' pattern, one using
generic vector types and the other using SSE intrinsics.

The presence of the bitcasts between SSE types prevents the recognition of the
select.

#include <x86intrin.h>

__v16qi cmp_i8_sel_v16i8(__v16qi a, __v16qi b, __v16qi c, __v16qi d) {
  __v16qi cc = _mm_cmpeq_epi8(a, b);
  return (c & ~cc) | (d & cc);
}

__m128i cmp_i8_sel_m128i(__m128i a, __m128i b, __m128i c, __m128i d) {
  __m128i cc = _mm_cmpeq_epi8(a, b);
  return _mm_or_si128(_mm_andnot_si128(cc, c), _mm_and_si128(cc, d));
}

define <16 x i8> @cmp_i8_sel_v16i8(<16 x i8>, <16 x i8>, <16 x i8>, <16 x i8>)
{
  %5 = icmp eq <16 x i8> %0, %1
  %6 = select <16 x i1> %5, <16 x i8> %3, <16 x i8> %2
  ret <16 x i8> %6
}

define <2 x i64> @cmp_i8_sel_m128i(<2 x i64>, <2 x i64>, <2 x i64>, <2 x i64>)
{
  %5 = bitcast <2 x i64> %0 to <16 x i8>
  %6 = bitcast <2 x i64> %1 to <16 x i8>
  %7 = icmp eq <16 x i8> %5, %6
  %8 = sext <16 x i1> %7 to <16 x i8>
  %9 = bitcast <16 x i8> %8 to <2 x i64>
  %10 = xor <2 x i64> %9, <i64 -1, i64 -1>
  %11 = and <2 x i64> %10, %2
  %12 = and <2 x i64> %9, %3
  %13 = or <2 x i64> %11, %12
  ret <2 x i64> %13
}

Mind you, on X86 at least it doesn't affect final codegen:

cmp_i8_sel_v16i8:
  vpcmpeqb %xmm1, %xmm0, %xmm0
  vpblendvb %xmm0, %xmm3, %xmm2, %xmm0
  retq

cmp_i8_sel_m128i:
  vpcmpeqb %xmm1, %xmm0, %xmm0
  vpblendvb %xmm0, %xmm3, %xmm2, %xmm0
  retq

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