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digitalmars.D.bugs - [Issue 11508] New: [REG 2.064] Wrong code with -O on x86_64 for char comparisons

reply d-bugmail puremagic.com writes:
https://d.puremagic.com/issues/show_bug.cgi?id=11508

           Summary: [REG 2.064] Wrong code with -O on x86_64 for char
                    comparisons
           Product: D
           Version: D2
          Platform: x86_64
        OS/Version: All
            Status: NEW
          Keywords: wrong-code
          Severity: regression
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: thecybershadow gmail.com



06:39:58 EET ---
bool isWordChar(char c)
{
    return c=='_' || c=='-' || c=='+' || c=='.';
}

void main()
{
    assert(isWordChar('_'));
}

"dmd -O -m64 -run test.d" will cause the above assert to trip.

Happens with 2.064.2 and git HEAD, doesn't happen with 2.063.

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Nov 12 2013
next sibling parent d-bugmail puremagic.com writes:
https://d.puremagic.com/issues/show_bug.cgi?id=11508


tchajed+d gmail.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |tchajed+d gmail.com



I wasn't able to isolate the issue in the compiler, but it looks like starting
at
https://github.com/D-Programming-Language/dmd/commit/fd999804a0d79fcbbfac39191d4e8f4ba7872467
an optimization was added for sequences of OR operations that is doing
something strange to this code. Just prior to this commit the isWordChar
function looked like this (in earlier versions there was no optimization and
the code just did a straightforward sequence of cmp and je):

0000000000000050 <_D4dbug10isWordCharFaZb>:
  50:    55                       push   %rbp
  51:    48 8b ec                 mov    %rsp,%rbp
  54:    48 83 ec 10              sub    $0x10,%rsp
  58:    89 7d f8                 mov    %edi,-0x8(%rbp)
  5b:    0f b6 45 f8              movzbl -0x8(%rbp),%eax
  5f:    83 c0 d5                 add    $0xffffffd5,%eax
  62:    83 f8 34                 cmp    $0x34,%eax
  65:    77 0a                    ja     71 <_D4dbug10isWordCharFaZb+0x21>
  67:    b9 0d 00 00 00           mov    $0xd,%ecx
  6c:    0f a3 c1                 bt     %eax,%ecx
  6f:    72 04                    jb     75 <_D4dbug10isWordCharFaZb+0x25>
  71:    31 c0                    xor    %eax,%eax
  73:    eb 05                    jmp    7a <_D4dbug10isWordCharFaZb+0x2a>
  75:    b8 01 00 00 00           mov    $0x1,%eax
  7a:    48 8b e5                 mov    %rbp,%rsp
  7d:    5d                       pop    %rbp
  7e:    c3                       retq

While afterward it looks like (but only on X86_64):
  70:    55                       push   %rbp
  71:    48 8b ec                 mov    %rsp,%rbp
  74:    48 83 ec 10              sub    $0x10,%rsp
  78:    89 7d f8                 mov    %edi,-0x8(%rbp)
  7b:    0f b6 45 f8              movzbl -0x8(%rbp),%eax
  7f:    83 c0 d5                 add    $0xffffffd5,%eax
  82:    83 f8 34                 cmp    $0x34,%eax
  85:    77 0f                    ja     96 <_D4dbug10isWordCharFaZb+0x26>
  87:    48 b9 0d 00 00 00 00     movabs $0x1000000000000d,%rcx
  8e:    00 10 00
  91:    0f a3 c1                 bt     %eax,%ecx
  94:    72 04                    jb     9a <_D4dbug10isWordCharFaZb+0x2a>
  96:    31 c0                    xor    %eax,%eax
  98:    eb 05                    jmp    9f <_D4dbug10isWordCharFaZb+0x2f>
  9a:    b8 01 00 00 00           mov    $0x1,%eax
  9f:    48 8b e5                 mov    %rbp,%rsp
  a2:    5d                       pop    %rbp
  a3:    c3                       retq

I don't understand the codebase well enough to see how to fix the issue, but
hope this helps!

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Nov 15 2013
prev sibling next sibling parent d-bugmail puremagic.com writes:
https://d.puremagic.com/issues/show_bug.cgi?id=11508


yebblies <yebblies gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |pull
                 CC|                            |yebblies gmail.com





   87:    48 b9 0d 00 00 00 00     movabs $0x1000000000000d,%rcx
   8e:    00 10 00
   91:    0f a3 c1                 bt     %eax,%ecx


The error is here                           ^^^^^^^^

https://github.com/D-Programming-Language/dmd/pull/2776

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Commits pushed to master at https://github.com/D-Programming-Language/dmd

https://github.com/D-Programming-Language/dmd/commit/f0e66ee8779936795fdb799a203b181371b38f7f
Issue 11508 - [REG 2.064] Wrong code with -O on x86_64 for char comparisons

https://github.com/D-Programming-Language/dmd/commit/51125bbed57caad4d326419470be07790915de5a


Issue 11508 - [REG 2.064] Wrong code with -O on x86_64 for char comparisons

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Nov 16 2013
prev sibling next sibling parent d-bugmail puremagic.com writes:
https://d.puremagic.com/issues/show_bug.cgi?id=11508


tchajed+d gmail.com changed:

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



Looks fixed in master now. yebblies, you can go ahead and claim Facebook's bug
bounty over at
https://www.bountysource.com/issues/1325896-reg-2-064-wrong-code-with-o-on-x86_64-for-char-comparisons
for this fix!

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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Commit pushed to dmd-1.x at https://github.com/D-Programming-Language/dmd

https://github.com/D-Programming-Language/dmd/commit/e3f5bb6040e4889932d3a1f06b0cd812e91790f1


Issue 11508 - [REG 2.064] Wrong code with -O on x86_64 for char comparisons

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prev sibling parent d-bugmail puremagic.com writes:
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 Looks fixed in master now. yebblies, you can go ahead and claim Facebook's bug
 bounty over at
 https://www.bountysource.com/issues/1325896-reg-2-064-wrong-code-with-o-on-x86_64-for-char-comparisons
 for this fix!


$$$

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Nov 16 2013