This patch fixes some very odd (unanticipated) code generation by
compare_by_pieces with -m32 -mavx, since the recent addition of the
cbranchoi4 pattern.  The issue is that cbranchoi4 is available with
TARGET_AVX, but cbranchti4 is currently conditional on TARGET_64BIT
which results in the odd behaviour (thanks to OPTAB_WIDEN) that with
-m32 -mavx, compare_by_pieces ends up (inefficiently) widening 128-bit
comparisons to 256-bits before performing PTEST.

This patch fixes this by providing a cbranchti4 pattern that's available
with either TARGET_64BIT or TARGET_SSE4_1.

For the test case below (again from PR 104610):

int foo(char *a)
{
    static const char t[] = "0123456789012345678901234567890";
    return __builtin_memcmp(a, &t[0], sizeof(t)) == 0;
}

GCC with -m32 -O2 -mavx currently produces the bonkers:

foo:    pushl   %ebp
        movl    %esp, %ebp
        andl    $-32, %esp
        subl    $64, %esp
        movl    8(%ebp), %eax
        vmovdqa .LC0, %xmm4
        movl    $0, 48(%esp)
        vmovdqu (%eax), %xmm2
        movl    $0, 52(%esp)
        movl    $0, 56(%esp)
        movl    $0, 60(%esp)
        movl    $0, 16(%esp)
        movl    $0, 20(%esp)
        movl    $0, 24(%esp)
        movl    $0, 28(%esp)
        vmovdqa %xmm2, 32(%esp)
        vmovdqa %xmm4, (%esp)
        vmovdqa (%esp), %ymm5
        vpxor   32(%esp), %ymm5, %ymm0
        vptest  %ymm0, %ymm0
        jne     .L2
        vmovdqu 16(%eax), %xmm7
        movl    $0, 48(%esp)
        movl    $0, 52(%esp)
        vmovdqa %xmm7, 32(%esp)
        vmovdqa .LC1, %xmm7
        movl    $0, 56(%esp)
        movl    $0, 60(%esp)
        movl    $0, 16(%esp)
        movl    $0, 20(%esp)
        movl    $0, 24(%esp)
        movl    $0, 28(%esp)
        vmovdqa %xmm7, (%esp)
        vmovdqa (%esp), %ymm1
        vpxor   32(%esp), %ymm1, %ymm0
        vptest  %ymm0, %ymm0
        je      .L6
.L2:    movl    $1, %eax
        xorl    $1, %eax
        vzeroupper
        leave
        ret
.L6:    xorl    %eax, %eax
        xorl    $1, %eax
        vzeroupper
        leave
        ret

with this patch, we now generate the (slightly) more sensible:

foo:    vmovdqa .LC0, %xmm0
        movl    4(%esp), %eax
        vpxor   (%eax), %xmm0, %xmm0
        vptest  %xmm0, %xmm0
        jne     .L2
        vmovdqa .LC1, %xmm0
        vpxor   16(%eax), %xmm0, %xmm0
        vptest  %xmm0, %xmm0
        je      .L5
.L2:    movl    $1, %eax
        xorl    $1, %eax
        ret
.L5:    xorl    %eax, %eax
        xorl    $1, %eax
        ret


This patch has been tested on x86_64-pc-linux-gnu with make bootstrap
and make -k check, both with and without --target_board=unix{-m32}
with no new failures.  Ok for mainline?


2023-06-27  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
        * config/i386/i386-expand.cc (ix86_expand_branch): Also use ptest
        for TImode comparisons on 32-bit architectures.
        * config/i386/i386.md (cbranch<mode>4): Change from SDWIM to
        SWIM1248x to exclude/avoid TImode being conditional on -m64.
        (cbranchti4): New define_expand for TImode on both TARGET_64BIT
        and/or with TARGET_SSE4_1.
        * config/i386/predicates.md (ix86_timode_comparison_operator):
        New predicate that depends upon TARGET_64BIT.
        (ix86_timode_comparison_operand): Likewise.

gcc/testsuite/ChangeLog
        * gcc.target/i386/pieces-memcmp-2.c: New test case.


Thanks in advance,
Roger
--