[Bug c/28306] const / pure call with ignored argument emitted.

[steven at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=28306

Steven Bosscher  changed:

   What|Removed |Added

   Last reconfirmed|2006-07-07 17:30:13 |2019-3-5
   Host|i686-pc-linux-gnu   |

--- Comment #4 from Steven Bosscher  ---
GCC trunk today on x86-64 produces:

gen_x86_64_shrd(int):
xorl%eax, %eax
ret
ok(int):
movl$1, %eax
ret
ix86_split_ashr(int):
testl   %edi, %edi
movl$ok(int), %eax
movl$gen_x86_64_shrd(int), %edx
cmove   %rdx, %rax
xorl%edi, %edi
jmp *%rax


FWIW clang trunk also does not optimize this, yielding:
ix86_split_ashr(int):   # @ix86_split_ashr(int)
testl   %edi, %edi
movl$gen_x86_64_shrd(int), %eax
movl$ok(int), %ecx
cmoveq  %rax, %rcx
xorl%edi, %edi
jmpq*%rcx   # TAILCALL
ok(int):# @ok(int)
movl$1, %eax
retq
gen_x86_64_shrd(int):  # @gen_x86_64_shrd(int)
xorl%eax, %eax
retq


ICC 19.0.1 _does_ optimize, resulting in:
ix86_split_ashr(int):
ret #24.1
_INTERNALf242c0c5::gen_x86_64_shrd(int):
xorl  %eax, %eax#6.10
ret #6.10
_INTERNALf242c0c5::ok(int):
movl  $1, %eax  #12.10
ret #12.10

[Bug c/28306] const / pure call with ignored argument emitted.

[rguenth at gcc dot gnu dot org]

--- Comment #3 from rguenth at gcc dot gnu dot org  2008-01-13 18:22 ---
This works for 'const' functions because they stick on the function type as
well.
The attributes are only on the DECL and do not get merged and transfered to the
resulting function type of the COND_EXPR.

So this again asks for streamlining attributes on types vs. decls.


-- 

rguenth at gcc dot gnu dot org changed:

   What|Removed |Added

 CC||rguenth at gcc dot gnu dot
   ||org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28306

[Bug c/28306] const / pure call with ignored argument emitted.

[rguenth at gcc dot gnu dot org]

--- Comment #2 from rguenth at gcc dot gnu dot org  2006-07-07 17:30 ---
Confirmed.


-- 

rguenth at gcc dot gnu dot org changed:

   What|Removed |Added

 Status|UNCONFIRMED |NEW
 Ever Confirmed|0   |1
   Last reconfirmed|-00-00 00:00:00 |2006-07-07 17:30:13
   date||


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28306

[Bug c/28306] const / pure call with ignored argument emitted.

[amylaar at gcc dot gnu dot org]

--- Comment #1 from amylaar at gcc dot gnu dot org  2006-07-07 16:54 ---
Created an attachment (id=11850)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=11850&action=view)
test case

The available source code for the functions allows the compiler to
see that the called functions are const.
This should be sufficient for the compiler to figure out the call is not
needed.
Likewise, the pure attributes should also be sufficient to figure this out.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28306