[Bug inline-asm/98847] Miscompilation with c++17, templates, and register keyword

[programmerjake at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98847

--- Comment #12 from programmerjake at gmail dot com ---
(In reply to Jakub Jelinek from comment #11)
> Fixed.

Thanks!!

[Bug inline-asm/98847] Miscompilation with c++17, templates, and register keyword

[programmerjake at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98847

--- Comment #8 from programmerjake at gmail dot com ---
Can the fix for this be backported to gcc 8 and 9 too? Thanks!

[Bug inline-asm/98847] Miscompilation with c++17, templates, and register keyword

[programmerjake at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98847

--- Comment #4 from programmerjake at gmail dot com ---
(In reply to Jakub Jelinek from comment #3)
> Created attachment 50066 [details]
> gcc11-pr98847.patch
> 
> Untested fix.

That will probably also fix bug #98846

[Bug inline-asm/98847] New: Miscompilation with c++17, templates, and register keyword

[programmerjake at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98847

Bug ID: 98847
   Summary: Miscompilation with c++17, templates, and register
keyword
   Product: gcc
   Version: 10.2.0
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: inline-asm
  Assignee: unassigned at gcc dot gnu.org
  Reporter: programmerjake at gmail dot com
  Target Milestone: ---
  Host: x86_64-linux-gnu
Target: x86_64-linux-gnu

In:
https://gcc.godbolt.org/z/49xoKP

With the following code:

template 
int template_get_edx() {
register int edx asm("edx");
asm("movl $1234, %%edx\n\t# reg=%0" : "=r"(edx));
return edx;
}

template int template_get_edx();

With: -O -Wall -std=c++17

Miscompiles, allocating %eax to the C++-level edx variable.

It's possible the C++ frontend is removing the register keyword before
finishing parsing since it also incorrectly warns here (bug #98846)

produces:
_Z16template_get_edxIvEiv:
.LFB1:
.file 1 "./example.cpp"
.loc 1 2 5 view -0
.cfi_startproc
.loc 1 4 5 is_stmt 0 view .LVU1
#APP
# 4 "./example.cpp" 1
movl $1234, %edx
# reg=%eax
# 0 "" 2
.LVL0:
.loc 1 6 1 view .LVU2
#NO_APP
ret

[Bug c++/98846] New: Spurious -Wregister warning

[programmerjake at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98846

Bug ID: 98846
   Summary: Spurious -Wregister warning
   Product: gcc
   Version: 10.2.0
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c++
  Assignee: unassigned at gcc dot gnu.org
  Reporter: programmerjake at gmail dot com
  Target Milestone: ---

In:
https://gcc.godbolt.org/z/49xoKP

With the following code:

template 
int template_get_edx() {
register int edx asm("edx");
asm("movl $1234, %%edx\n\t# reg=%0" : "=r"(edx));
return edx;
}

template int template_get_edx();

With: -O -Wall -std=c++17

produces:
: In instantiation of 'int template_get_edx() [with T = void]':
:8:37:   required from here
:3:18: warning: ISO C++17 does not allow 'register' storage class
specifier [-Wregister]
3 | register int edx asm("edx");

I think that warning is spurious because the `register` keyword is required for
clang to not ignore the asm("edx").