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i386: Add cbranchti4 pattern to i386.md (for -m32 compare_by_pieces).

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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

2023-06-28  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.
This commit is contained in:
Roger Sayle 2023-06-28 11:11:34 +01:00
parent c027592d39
commit 4afbebcdc5
4 changed files with 45 additions and 3 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

3
gcc/config/i386/i386-expand.cc
View file

@ -2365,6 +2365,7 @@ ix86_expand_branch (enum rtx_code code, rtx op0, rtx op1, rtx label)
/* Handle special case - vector comparsion with boolean result, transform
it using ptest instruction. */
if (GET_MODE_CLASS (mode) == MODE_VECTOR_INT
|| (mode == TImode && !TARGET_64BIT)
|| mode == OImode)
{
rtx flag = gen_rtx_REG (CCZmode, FLAGS_REG);
@ -2372,7 +2373,7 @@ ix86_expand_branch (enum rtx_code code, rtx op0, rtx op1, rtx label)
gcc_assert (code == EQ || code == NE);
if (mode == OImode)
if (GET_MODE_CLASS (mode) != MODE_VECTOR_INT)
{
op0 = lowpart_subreg (p_mode, force_reg (mode, op0), mode);
op1 = lowpart_subreg (p_mode, force_reg (mode, op1), mode);

20
gcc/config/i386/i386.md
View file

@ -1352,8 +1352,8 @@
(define_expand "cbranch<mode>4"
[(set (reg:CC FLAGS_REG)
(compare:CC (match_operand:SDWIM 1 "nonimmediate_operand")
(match_operand:SDWIM 2 "<general_operand>")))
(compare:CC (match_operand:SWIM1248x 1 "nonimmediate_operand")
(match_operand:SWIM1248x 2 "<general_operand>")))
(set (pc) (if_then_else
(match_operator 0 "ordered_comparison_operator"
[(reg:CC FLAGS_REG) (const_int 0)])
@ -1368,6 +1368,22 @@
DONE;
})
(define_expand "cbranchti4"
[(set (reg:CC FLAGS_REG)
(compare:CC (match_operand:TI 1 "nonimmediate_operand")
(match_operand:TI 2 "ix86_timode_comparison_operand")))
(set (pc) (if_then_else
(match_operator 0 "ix86_timode_comparison_operator"
[(reg:CC FLAGS_REG) (const_int 0)])
(label_ref (match_operand 3))
(pc)))]
"TARGET_64BIT || TARGET_SSE4_1"
{
ix86_expand_branch (GET_CODE (operands[0]),
operands[1], operands[2], operands[3]);
DONE;
})
(define_expand "cbranchoi4"
[(set (reg:CC FLAGS_REG)
(compare:CC (match_operand:OI 1 "nonimmediate_operand")

12
gcc/config/i386/predicates.md
View file

@ -1641,6 +1641,18 @@
(match_operand 0 "comparison_operator")
(match_operand 0 "ix86_trivial_fp_comparison_operator")))
;; Return true if we can perform this comparison on TImode operands.
(define_predicate "ix86_timode_comparison_operator"
(if_then_else (match_test "TARGET_64BIT")
(match_operand 0 "ordered_comparison_operator")
(match_operand 0 "bt_comparison_operator")))
;; Return true if this is a valid second operand for a TImode comparison.
(define_predicate "ix86_timode_comparison_operand"
(if_then_else (match_test "TARGET_64BIT")
(match_operand 0 "x86_64_general_operand")
(match_operand 0 "nonimmediate_operand")))
;; Nearly general operand, but accept any const_double, since we wish
;; to be able to drop them into memory rather than have them get pulled
;; into registers.

13
gcc/testsuite/gcc.target/i386/pieces-memcmp-2.c Normal file
View file

@ -0,0 +1,13 @@
/* { dg-do compile { target ia32 } } */
/* { dg-options "-O2 -mavx2" } */
int foo(char *a)
{
static const char t[] = "0123456789012345678901234567890";
return __builtin_memcmp(a, &t[0], sizeof(t)) == 0;
}
/* { dg-final { scan-assembler-not "movl\[ \\t]*\\\$0," } } */
/* { dg-final { scan-assembler-not "vptest\[ \\t]*%ymm" } } */
/* { dg-final { scan-assembler-times "vptest\[ \\t]*%xmm" 2 } } */