[Issue 14436] Optimizer fails to remove comparison loop when comparing array against null

Apr 10, 2015

yebblies

Apr 12, 2015

github-bugzilla@puremagic.com

Apr 12, 2015

github-bugzilla@puremagic.com

Apr 15, 2015

Apr 15, 2015

Apr 16, 2015

Apr 16, 2015

Jun 10, 2015

Jun 17, 2015

github-bugzilla@puremagic.com

Jun 17, 2015

github-bugzilla@puremagic.com

Jun 19, 2015

Marc Schütz

Dec 17, 2022

Iain Buclaw

Dec 13

dlangBugzillaToGithub

https://issues.dlang.org/show_bug.cgi?id=14436 yebblies <yebblies@gmail.com> changed: What |Removed |Added ---------------------------------------------------------------------------- Keywords| |pull --- Comment #1 from yebblies <yebblies@gmail.com> --- https://github.com/D-Programming-Language/dmd/pull/4574 --

https://issues.dlang.org/show_bug.cgi?id=14436 --- Comment #2 from github-bugzilla@puremagic.com --- Commits pushed to master at https://github.com/D-Programming-Language/dmd https://github.com/D-Programming-Language/dmd/commit/7660158f16b9c988d8ff16592ee442051ea95ffa Fix Issue 14436 - Optimizer fails to remove comparison loop when comparing array against null https://github.com/D-Programming-Language/dmd/commit/6f5a3cde5778e263d53d49f4546b668652ca89ae Merge pull request #4574 from yebblies/issue14436 Issue 14436 - Optimizer fails to remove comparison loop when comparing array against null --

https://issues.dlang.org/show_bug.cgi?id=14436 Marc Schütz <schuetzm@gmx.net> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|RESOLVED |REOPENED CC| |schuetzm@gmx.net Resolution|FIXED |--- --- Comment #3 from Marc Schütz <schuetzm@gmx.net> --- Comparing with an empty array or string literal still generates suboptimal code: bool isEmpty(string s) { return s == ""; } # dmd -c -O -inline -release xx.d 0000000000000000 <_D2xx7isEmptyFAyaZb>: 0: 55 push %rbp 1: 48 8b ec mov %rsp,%rbp 4: 48 83 ec 10 sub $0x10,%rsp 8: 48 89 7d f0 mov %rdi,-0x10(%rbp) c: 48 89 75 f8 mov %rsi,-0x8(%rbp) 10: 48 3b 3d 00 00 00 00 cmp 0x0(%rip),%rdi # 17 <_D2xx7isEmptyFAyaZb+0x17> 17: 75 15 jne 2e <_D2xx7isEmptyFAyaZb+0x2e> 19: 48 8b 75 f8 mov -0x8(%rbp),%rsi 1d: 48 8b 3d 00 00 00 00 mov 0x0(%rip),%rdi # 24 <_D2xx7isEmptyFAyaZb+0x24> 24: 48 8b 4d f0 mov -0x10(%rbp),%rcx 28: 33 c0 xor %eax,%eax 2a: f3 a6 repz cmpsb %es:(%rdi),%ds:(%rsi) 2c: 74 04 je 32 <_D2xx7isEmptyFAyaZb+0x32> 2e: 31 c0 xor %eax,%eax 30: eb 05 jmp 37 <_D2xx7isEmptyFAyaZb+0x37> 32: b8 01 00 00 00 mov $0x1,%eax 37: 48 8b e5 mov %rbp,%rsp 3a: 5d pop %rbp 3b: c3 retq Reopening, as it is a closely related enhancement (though strictly speaking not identical). --

April 16, 2015

[Issue 14436] Optimizer fails to remove comparison loop when comparing array against null

Posted by Marc Schütz

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Marc Schütz

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https://issues.dlang.org/show_bug.cgi?id=14436

--- Comment #5 from Marc Schütz <schuetzm@gmx.net> ---
(In reply to yebblies from comment #4)
> By empty array do you mean empty array literal?
> 
> eg assert(x != []);

Yes, it should read "empty array [literal] or string literal".

In fact, the code generated for `int[]` instead of `string` looks even worse; there is a "call" instruction in it:

0000000000000000 <_D2xx7isEmptyFAiZb>:
   0:    55                       push   %rbp
   1:    48 8b ec                 mov    %rsp,%rbp
   4:    48 83 ec 30              sub    $0x30,%rsp
   8:    48 89 7d f0              mov    %rdi,-0x10(%rbp)
   c:    48 89 75 f8              mov    %rsi,-0x8(%rbp)
  10:    48 31 f6                 xor    %rsi,%rsi
  13:    48 bf 00 00 00 00 00     movabs $0x0,%rdi
  1a:    00 00 00
  1d:    e8 00 00 00 00           callq  22 <_D2xx7isEmptyFAiZb+0x22>
  22:    48 89 c1                 mov    %rax,%rcx
  25:    48 31 c0                 xor    %rax,%rax
  28:    48 89 45 e0              mov    %rax,-0x20(%rbp)
  2c:    48 89 4d e8              mov    %rcx,-0x18(%rbp)
  30:    48 89 45 d0              mov    %rax,-0x30(%rbp)
  34:    48 89 4d d8              mov    %rcx,-0x28(%rbp)
  38:    48 8b 55 f0              mov    -0x10(%rbp),%rdx
  3c:    48 3b 55 e0              cmp    -0x20(%rbp),%rdx
  40:    75 1a                    jne    5c <_D2xx7isEmptyFAiZb+0x5c>
  42:    48 85 d2                 test   %rdx,%rdx
  45:    74 19                    je     60 <_D2xx7isEmptyFAiZb+0x60>
  47:    48 8b 75 f8              mov    -0x8(%rbp),%rsi
  4b:    48 8b 7d d8              mov    -0x28(%rbp),%rdi
  4f:    48 89 d1                 mov    %rdx,%rcx
  52:    48 c1 e1 02              shl    $0x2,%rcx
  56:    33 c0                    xor    %eax,%eax
  58:    f3 a6                    repz cmpsb %es:(%rdi),%ds:(%rsi)
  5a:    74 04                    je     60 <_D2xx7isEmptyFAiZb+0x60>
  5c:    31 c0                    xor    %eax,%eax
  5e:    eb 05                    jmp    65 <_D2xx7isEmptyFAiZb+0x65>
  60:    b8 01 00 00 00           mov    $0x1,%eax
  65:    48 8b e5                 mov    %rbp,%rsp
  68:    5d                       pop    %rbp
  69:    c3                       retq

--

https://issues.dlang.org/show_bug.cgi?id=14436 --- Comment #6 from yebblies <yebblies@gmail.com> --- Ok, I'll have a look. This can probably be special-cased, although there is a long-standing problem that the optimizer doesn't look at constant data correctly. --

https://issues.dlang.org/show_bug.cgi?id=14436 Andrei Alexandrescu <andrei@erdani.com> changed: What |Removed |Added ---------------------------------------------------------------------------- Version|D1 & D2 |D2 --

https://issues.dlang.org/show_bug.cgi?id=14436 --- Comment #7 from github-bugzilla@puremagic.com --- Commits pushed to stable at https://github.com/D-Programming-Language/dmd https://github.com/D-Programming-Language/dmd/commit/7660158f16b9c988d8ff16592ee442051ea95ffa Fix Issue 14436 - Optimizer fails to remove comparison loop when comparing array against null https://github.com/D-Programming-Language/dmd/commit/6f5a3cde5778e263d53d49f4546b668652ca89ae Merge pull request #4574 from yebblies/issue14436 --

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