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

[d-bugmail at puremagic.com]

https://d.puremagic.com/issues/show_bug.cgi?id=11508


tchajed+d at gmail.com changed:

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


--- Comment #1 from tchajed+d at gmail.com 2013-11-15 19:20:32 PST ---
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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