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List:       gcc-bugs
Subject:    [Bug tree-optimization/97260] New: memcmp of constant string and local constant array not folded
From:       "msebor at gcc dot gnu.org via Gcc-bugs" <gcc-bugs () gcc ! gnu ! org>
Date:       2020-09-30 23:27:48
Message-ID: bug-97260-4 () http ! gcc ! gnu ! org/bugzilla/
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97260

            Bug ID: 97260
           Summary: memcmp of constant string and local constant array not
                    folded
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

GCC fails to fold the memcmp call below into a constant.  Clang folds it
successfully.

$ cat x.c && gcc -O2 -S -Wall -Wextra -fdump-tree-optimized=/dev/stdout
-o/dev/stdout x.c
int f (void)
{
  const char a[] = "1234";
  return __builtin_memcmp (a, "1234", 4);
}
        .file   "x.c"
        .text

;; Function f (f, funcdef_no=0, decl_uid=1931, cgraph_uid=1, symbol_order=0)

f ()
{
  const char a[5];
  int _3;

  <bb 2> [local count: 1073741824]:
  a = "1234";
  _3 = __builtin_memcmp (&a, "1234", 4);
  a ={v} {CLOBBER};
  return _3;

}


        .section        .rodata.str1.1,"aMS",@progbits,1
.LC0:
        .string "1234"
        .text
        .p2align 4
        .globl  f
        .type   f, @function
f:
.LFB0:
        .cfi_startproc
        subq    $24, %rsp
        .cfi_def_cfa_offset 32
        movl    $4, %edx
        movl    $.LC0, %esi
        leaq    11(%rsp), %rdi
        movl    $875770417, 11(%rsp)
        movb    $0, 15(%rsp)
        call    memcmp
        addq    $24, %rsp
        .cfi_def_cfa_offset 8
        ret
        .cfi_endproc
.LFE0:
        .size   f, .-f
        .ident  "GCC: (GNU) 11.0.0 20200930 (experimental)"
        .section        .note.GNU-stack,"",@progbits=
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