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* [Bug rtl-optimization/64907] New: Suboptimal code (saving rbx on stack in order to save another reg in rbx)
@ 2015-02-02 18:36 vda.linux at googlemail dot com
2015-02-02 19:09 ` [Bug rtl-optimization/64907] " hjl.tools at gmail dot com
0 siblings, 1 reply; 2+ messages in thread
From: vda.linux at googlemail dot com @ 2015-02-02 18:36 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64907
Bug ID: 64907
Summary: Suboptimal code (saving rbx on stack in order to save
another reg in rbx)
Product: gcc
Version: 4.7.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: vda.linux at googlemail dot com
void put_16bit(unsigned short v);
void put_32bit(unsigned v)
{
put_16bit(v);
put_16bit(v >> 16);
}
With gcc 4.7.2 the above compiles to the following assembly:
put_32bit:
pushq %rbx
movl %edi, %ebx
andl $65535, %edi
call put_16bit
movl %ebx, %edi
popq %rbx
shrl $16, %edi
jmp put_16bit
Code saves %rbx on stack only in order to save %edi to %ebx.
A simpler alternative is to just save %rdi on stack:
put_32bit:
pushq %rdi
andl $65535, %edi
call put_16bit
popq %rdi
shrl $16, %edi
jmp put_16bit
^ permalink raw reply [flat|nested] 2+ messages in thread
* [Bug rtl-optimization/64907] Suboptimal code (saving rbx on stack in order to save another reg in rbx)
2015-02-02 18:36 [Bug rtl-optimization/64907] New: Suboptimal code (saving rbx on stack in order to save another reg in rbx) vda.linux at googlemail dot com
@ 2015-02-02 19:09 ` hjl.tools at gmail dot com
0 siblings, 0 replies; 2+ messages in thread
From: hjl.tools at gmail dot com @ 2015-02-02 19:09 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64907
H.J. Lu <hjl.tools at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Last reconfirmed| |2015-02-02
CC| |vmakarov at redhat dot com
Version|4.7.2 |5.0
Ever confirmed|0 |1
--- Comment #1 from H.J. Lu <hjl.tools at gmail dot com> ---
Still happens with 5.0.
^ permalink raw reply [flat|nested] 2+ messages in thread
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2015-02-02 18:36 [Bug rtl-optimization/64907] New: Suboptimal code (saving rbx on stack in order to save another reg in rbx) vda.linux at googlemail dot com
2015-02-02 19:09 ` [Bug rtl-optimization/64907] " hjl.tools at gmail dot com
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