[Bug middle-end/95886] New: suboptimal memcpy with embedded zero bytes

[Bug middle-end/95886] New: suboptimal memcpy with embedded zero bytes

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95886

            Bug ID: 95886
           Summary: suboptimal memcpy with embedded zero bytes
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

While testing the fix for pr95189 I noticed that the memcpy expansion into
copy-by-pieces is less than optimal for sequences containing embedded null
bytes.  For example, in the test case below, the memcpy call in f() is expanded
into what looks like a more efficient sequence than the equivalent memcpy call
in g().  The only difference between the two is that the former copies a
sequence of non-zero bytes while among the bytes copied by the latter is a null
byte.  Clang emits the same code for g() as GCC does for f().

$ cat z.c && gcc -O2 -S -Wall -fdump-tree-optimized=/dev/stdout -o/dev/stdout
z.c
const char a[10] = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
const char b[10] = { 0, 1, 2, 3, 4, 5, 6, 7, 8 };

void f (void *d)
{
  __builtin_memcpy (d, a, 9);   // optimal
}

void g (void *d)
{
  __builtin_memcpy (d, b, 9);   // suboptimal
}


        .file   "z.c"
        .text

;; Function f (f, funcdef_no=0, decl_uid=1932, cgraph_uid=1, symbol_order=2)

f (void * d)
{
  <bb 2> [local count: 1073741824]:
  __builtin_memcpy (d_2(D), &a, 9); [tail call]
  return;

}


        .p2align 4
        .globl  f
        .type   f, @function
f:
.LFB0:
        .cfi_startproc
        movabsq $578437695752307201, %rax
        movb    $9, 8(%rdi)
        movq    %rax, (%rdi)
        ret
        .cfi_endproc
.LFE0:
        .size   f, .-f

;; Function g (g, funcdef_no=1, decl_uid=1935, cgraph_uid=2, symbol_order=3)

g (void * d)
{
  <bb 2> [local count: 1073741824]:
  __builtin_memcpy (d_2(D), &b, 9); [tail call]
  return;

}


        .p2align 4
        .globl  g
        .type   g, @function
g:
.LFB1:
        .cfi_startproc
        movq    b(%rip), %rax
        movq    %rax, (%rdi)
        movzbl  b+8(%rip), %eax
        movb    %al, 8(%rdi)
        ret
        .cfi_endproc
.LFE1:
        .size   g, .-g
        .globl  b
        .section        .rodata
        .align 8
        .type   b, @object
        .size   b, 10
b:
        .string ""
        .string "\001\002\003\004\005\006\007\b"
        .globl  a
        .align 8
        .type   a, @object
        .size   a, 10
a:
        .string "\001\002\003\004\005\006\007\b\t"
        .ident  "GCC: (GNU) 10.1.1 20200527"
        .section        .note.GNU-stack,"",@progbits

[Bug middle-end/95886] suboptimal memcpy with embedded zero bytes

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95886

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
     Ever confirmed|0                           |1
           Assignee|unassigned at gcc dot gnu.org      |msebor at gcc dot gnu.org
   Last reconfirmed|                            |2020-06-24

--- Comment #1 from Martin Sebor <msebor at gcc dot gnu.org> ---
I'm testing a fix.

[Bug middle-end/95886] suboptimal memcpy with embedded zero bytes

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95886

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=95887

--- Comment #2 from Martin Sebor <msebor at gcc dot gnu.org> ---
See also pr95887 for a related problem with memcmp.

[Bug middle-end/95886] suboptimal memcpy with embedded zero bytes

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95886

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |patch

--- Comment #3 from Martin Sebor <msebor at gcc dot gnu.org> ---
Patch: https://gcc.gnu.org/pipermail/gcc-patches/2020-July/549225.html

[Bug middle-end/95886] suboptimal memcpy with embedded zero bytes

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95886

--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Martin Sebor <msebor@gcc.gnu.org>:

https://gcc.gnu.org/g:d5803b9876b3d11c93d1a10fabb3fbb1c4a14bd6

commit r11-2231-gd5803b9876b3d11c93d1a10fabb3fbb1c4a14bd6
Author: Martin Sebor <msebor@redhat.com>
Date:   Mon Jul 20 12:06:18 2020 -0600

    Correct handling of constant representations containing embedded nuls.

    Resolves:
    PR middle-end/95189 - memcmp being wrongly stripped like strcm
    PR middle-end/95886 - suboptimal memcpy with embedded zero bytes

    gcc/ChangeLog:

            PR middle-end/95189
            PR middle-end/95886
            * builtins.c (inline_expand_builtin_string_cmp): Rename...
            (inline_expand_builtin_bytecmp): ...to this.
            (builtin_memcpy_read_str): Don't expect data to be nul-terminated.
            (expand_builtin_memory_copy_args): Handle object representations
            with embedded nul bytes.
            (expand_builtin_memcmp): Same.
            (expand_builtin_strcmp): Adjust call to naming change.
            (expand_builtin_strncmp): Same.
            * expr.c (string_constant): Create empty strings with nonzero size.
            * fold-const.c (c_getstr): Rename locals and update comments.
            * tree.c (build_string): Accept null pointer argument.
            (build_string_literal): Same.
            * tree.h (build_string): Provide a default.
            (build_string_literal): Same.

    gcc/testsuite/ChangeLog:

            PR middle-end/95189
            PR middle-end/95886
            * gcc.dg/memcmp-pr95189.c: New test.
            * gcc.dg/strncmp-3.c: New test.
            * gcc.target/i386/memcpy-pr95886.c: New test.

[Bug middle-end/95886] suboptimal memcpy with embedded zero bytes

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95886

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|ASSIGNED                    |RESOLVED

--- Comment #5 from Martin Sebor <msebor at gcc dot gnu.org> ---
Fixed in r11-2231.

[Bug middle-end/95886] suboptimal memcpy with embedded zero bytes

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95886

--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Martin Sebor <msebor@gcc.gnu.org>:

https://gcc.gnu.org/g:8598657c607500512075f6c4ee3b10460c94903d

commit r11-2298-g8598657c607500512075f6c4ee3b10460c94903d
Author: Martin Sebor <msebor@redhat.com>
Date:   Thu Jul 23 14:08:22 2020 -0600

    Restrict test to LP64.

    gcc/testsuite/ChangeLog:

            PR testsuite/95886
            * gcc.target/i386/memcpy-pr95886.c: Restrict test to LP64.

[Bug middle-end/95886] suboptimal memcpy with embedded zero bytes

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95886

--- Comment #7 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by H.J. Lu <hjl@gcc.gnu.org>:

https://gcc.gnu.org/g:b0e5ec934e7a7473275326e2aee58eaf252cdff1

commit r11-2301-gb0e5ec934e7a7473275326e2aee58eaf252cdff1
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Thu Jul 23 19:14:06 2020 -0700

    Restrict PR middle-end/95886 x86 test to !ia32

    Since gcc.target/i386/memcpy-pr95886.c requires 64-bit register, restrict
    it to !ia32.

            PR middle-end/95886
            * gcc.target/i386/memcpy-pr95886.c: Restrict test to !ia32.

[Bug middle-end/95886] suboptimal memcpy with embedded zero bytes

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95886

--- Comment #8 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-10 branch has been updated by Martin Sebor
<msebor@gcc.gnu.org>:

https://gcc.gnu.org/g:e4c9aac98611f63847ef6c57916808d9a2d7abcb

commit r10-8871-ge4c9aac98611f63847ef6c57916808d9a2d7abcb
Author: Martin Sebor <msebor@redhat.com>
Date:   Thu Oct 8 12:35:01 2020 -0600

    Correct handling of constant representations containing embedded nuls
(backport from trunk).

    Resolves:
    PR middle-end/95189 - memcmp being wrongly stripped like strcm
    PR middle-end/95886 - suboptimal memcpy with embedded zero bytes

    gcc/ChangeLog:

            PR middle-end/95189
            PR middle-end/95886
            * builtins.c (inline_expand_builtin_string_cmp): Rename...
            (inline_expand_builtin_bytecmp): ...to this.
            (builtin_memcpy_read_str): Don't expect data to be nul-terminated.
            (expand_builtin_memory_copy_args): Handle object representations
            with embedded nul bytes.
            (expand_builtin_memcmp): Same.
            (expand_builtin_strcmp): Adjust call to naming change.
            (expand_builtin_strncmp): Same.
            * expr.c (string_constant): Create empty strings with nonzero size.
            * fold-const.c (c_getstr): Rename locals and update comments.
            * tree.c (build_string): Accept null pointer argument.
            (build_string_literal): Same.
            * tree.h (build_string): Provide a default.
            (build_string_literal): Same.

    gcc/testsuite/ChangeLog:

            PR middle-end/95189
            PR middle-end/95886
            * gcc.dg/memcmp-pr95189.c: New test.
            * gcc.dg/strncmp-3.c: New test.
            * gcc.target/i386/memcpy-pr95886.c: New test.

[Bug middle-end/95886] suboptimal memcpy with embedded zero bytes

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95886

--- Comment #9 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-10 branch has been updated by Jakub Jelinek
<jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:75a016e24a335db9c93ccd2478433adfe773d898

commit r10-8903-g75a016e24a335db9c93ccd2478433adfe773d898
Author: Martin Sebor <msebor@redhat.com>
Date:   Thu Jul 23 14:08:22 2020 -0600

    Restrict test to LP64.

    gcc/testsuite/ChangeLog:

            PR testsuite/95886
            * gcc.target/i386/memcpy-pr95886.c: Restrict test to LP64.

    (cherry picked from commit 8598657c607500512075f6c4ee3b10460c94903d)

[Bug middle-end/95886] suboptimal memcpy with embedded zero bytes

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95886

--- Comment #10 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-10 branch has been updated by Jakub Jelinek
<jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:0cf293649b6c495249854133159ef66bf9c43904

commit r10-8904-g0cf293649b6c495249854133159ef66bf9c43904
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Thu Jul 23 19:14:06 2020 -0700

    Restrict PR middle-end/95886 x86 test to !ia32

    Since gcc.target/i386/memcpy-pr95886.c requires 64-bit register, restrict
    it to !ia32.

            PR middle-end/95886
            * gcc.target/i386/memcpy-pr95886.c: Restrict test to !ia32.

    (cherry picked from commit b0e5ec934e7a7473275326e2aee58eaf252cdff1)