[Issue 14943] dmd should inline more aggressively

Aug 21, 2015

hsteoh@quickfur.ath.cx

Aug 21, 2015

hsteoh@quickfur.ath.cx

Aug 21, 2015

Jun 06, 2016

Jun 06, 2016

Dec 17, 2022

Dec 13

dlangBugzillaToGithub

https://issues.dlang.org/show_bug.cgi?id=14943 hsteoh@quickfur.ath.cx changed: What |Removed |Added ---------------------------------------------------------------------------- Keywords| |performance --

August 21, 2015

[Issue 14943] dmd should inline more aggressively

Posted by hsteoh@quickfur.ath.cx

Permalink

hsteoh@quickfur.ath.cx

Permalink

https://issues.dlang.org/show_bug.cgi?id=14943

--- Comment #1 from hsteoh@quickfur.ath.cx ---
Further notes:
- gdc not only inlines the call trees of .empty, .front, .popFront, it also
applied other loop optimizations like strength reduction to refactor the a =>
a*7 into a += b; b += 7. Not sure if dmd is capable of doing this, but in any
case the opportunity is missed because .popFront was not inlined, so the
optimizer wouldn't have been able to apply strength reduction.

- gdc's aggressive inlining also allowed various loop counters and accumulators to be completely held in registers, while the function calls generated by dmd necessitated dereferencing addresses to stack variables, which is an extra layer of indirection. Again, a missed opportunity due to not inlining aggressively enough.

For reference, here's the inner loop produced by gdc:

  403b80:       89 d7                   mov    %edx,%edi
  403b82:       c1 ef 1f                shr    $0x1f,%edi
  403b85:       8d 34 3a                lea    (%rdx,%rdi,1),%esi
  403b88:       83 c2 07                add    $0x7,%edx
  403b8b:       83 e6 01                and    $0x1,%esi
  403b8e:       39 fe                   cmp    %edi,%esi
  403b90:       75 1e                   jne    403bb0 <int test.fun(int)+0x80>
  403b92:       89 c6                   mov    %eax,%esi
  403b94:       8d 14 cd 00 00 00 00    lea    0x0(,%rcx,8),%edx
  403b9b:       c1 ee 1f                shr    $0x1f,%esi
  403b9e:       01 f0                   add    %esi,%eax
  403ba0:       29 ca                   sub    %ecx,%edx
  403ba2:       d1 f8                   sar    %eax
  403ba4:       01 d0                   add    %edx,%eax
  403ba6:       83 c2 07                add    $0x7,%edx
  403ba9:       0f 1f 80 00 00 00 00    nopl   0x0(%rax)
  403bb0:       83 c1 01                add    $0x1,%ecx
  403bb3:       39 cb                   cmp    %ecx,%ebx
  403bb5:       75 c9                   jne    403b80 <int test.fun(int)+0x50>

--

https://issues.dlang.org/show_bug.cgi?id=14943 Ivan Kazmenko <gassa@mail.ru> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |gassa@mail.ru --

https://issues.dlang.org/show_bug.cgi?id=14943 Jack Stouffer <jack@jackstouffer.com> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |greensunny12@gmail.com --- Comment #2 from Jack Stouffer <jack@jackstouffer.com> --- *** Issue 16120 has been marked as a duplicate of this issue. *** --

https://issues.dlang.org/show_bug.cgi?id=14943 greenify <greeenify@gmail.com> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |greeenify@gmail.com --

https://issues.dlang.org/show_bug.cgi?id=14943 Iain Buclaw <ibuclaw@gdcproject.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Priority|P1 |P4 --

https://issues.dlang.org/show_bug.cgi?id=14943 --- Comment #3 from dlangBugzillaToGithub <robert.schadek@posteo.de> --- THIS ISSUE HAS BEEN MOVED TO GITHUB https://github.com/dlang/dmd/issues/19031 DO NOT COMMENT HERE ANYMORE, NOBODY WILL SEE IT, THIS ISSUE HAS BEEN MOVED TO GITHUB --

Forums