[Bug rtl-optimization/66152] suboptimal load bytes to stack

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66152

Jakub Jelinek  changed:

   What|Removed |Added

 CC||jakub at gcc dot gnu.org

--- Comment #5 from Jakub Jelinek  ---
That changed with r263511, which now treats the {0,1,2,3,4,5,6,7} initializer
like "\0\1\2\3\4\5\6\7", so that means even GCC 8 expanded the latter this way.

[Bug rtl-optimization/66152] suboptimal load bytes to stack

[SztfG at yandex dot ru]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66152

--- Comment #4 from SztfG at yandex dot ru ---
GCC from trunk doing this:

.Ltext0:
.LC0:
  .string ""
  .ascii "\001\002\003\004\005\006\007"
bar:
.LFB0:
  sub rsp, 24
  mov rax, QWORD PTR .LC0[rip]
  lea rdi, [rsp+8]
  mov QWORD PTR [rsp+8], rax
  call foo
.LVL0:
  add rsp, 24
  ret
.LFE0:

instead movabsq $506097522914230528, %rax

[Bug rtl-optimization/66152] suboptimal load bytes to stack

[me at xenu dot pl]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66152

Tomasz Konojacki  changed:

   What|Removed |Added

 CC||me at xenu dot pl

--- Comment #3 from Tomasz Konojacki  ---
gcc 8.1 generates the following code:

bar():
movabsq $506097522914230528, %rax
subq$24, %rsp
leaq8(%rsp), %rdi
movq%rax, 8(%rsp)
callfoo(char*)
addq$24, %rsp
ret

I believe this ticket should be closed.

[Bug rtl-optimization/66152] suboptimal load bytes to stack

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66152

--- Comment #2 from Andrew Pinski  ---
I think there might be already another bug about this same exact thing but I
can't seem to find it right now.

[Bug rtl-optimization/66152] suboptimal load bytes to stack

[SztfG at yandex dot ru]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66152

--- Comment #1 from SztfG at yandex dot ru ---
If array of char is initialized using string, gcc can use larger mov
instruction, like movabsq, movq, movl etc. but not movdqa, movaps or other xmm
But if zero byte appears in string, compiler always create a separate array and
copy it to stack, using various mov instruction, except xmm-based

void bar(void)
{
  char a[4] = \x00\x02\x03\x04;
  foo(a);
}

produces

.LC0:
.string 
.string \002\003\004

bar:
subq$24, %rsp
movl.LC0(%rip), %eax
movq%rsp, %rdi
movl%eax, (%rsp)
callfoo
addq$24, %rsp
ret