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* [Bug c/114097] New: Missed register optimization in _Noreturn functions
@ 2024-02-25 11:07 pskocik at gmail dot com
2024-02-25 13:12 ` [Bug c/114097] " hjl.tools at gmail dot com
` (7 more replies)
0 siblings, 8 replies; 9+ messages in thread
From: pskocik at gmail dot com @ 2024-02-25 11:07 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114097
Bug ID: 114097
Summary: Missed register optimization in _Noreturn functions
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: pskocik at gmail dot com
Target Milestone: ---
Consider a never-returning functions such as this:
#include<setjmp.h>
#include<stdio.h>
//_Noreturn
void noret(unsigned A, unsigned B, unsigned C, unsigned D, unsigned E, jmp_buf
Jb){
for(;A--;) puts("A");
for(;B--;) puts("B");
for(;C--;) puts("C");
for(;D--;) puts("D");
for(;E--;) puts("E");
longjmp(Jb,1);
}
https://godbolt.org/z/35YjrhjYq
In its prologue, gcc saves the arguments in call-preserved registers to
preserve them around the puts calls, and it does so the usual way: by (1)
pushing the old values of the call-preserved registers to the stack and (2)
actually moving the arguments into the call-preserved registers.
pushq %r15
movq %r9, %r15
pushq %r14
movl %edi, %r14d
pushq %r13
movl %esi, %r13d
pushq %r12
movl %edx, %r12d
pushq %rbp
movl %ecx, %ebp
pushq %rbx
movl %r8d, %ebx
pushq %rax
//...
Since this function demonstrably never returns, step 1 can be entirely elided
as the old values of the call-preserved registers won't ever need to be
restored
(desirably, gcc does not generate the would-be-dead restoration code):
movq %r9, %r15
movl %edi, %r14d
movl %esi, %r13d
movl %edx, %r12d
movl %ecx, %ebp
movl %r8d, %ebx
pushq %rax
//...
(Also desirable would be the unrealized tailoptimization of the longjmp call in
this case: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=10837)
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug c/114097] Missed register optimization in _Noreturn functions
2024-02-25 11:07 [Bug c/114097] New: Missed register optimization in _Noreturn functions pskocik at gmail dot com
@ 2024-02-25 13:12 ` hjl.tools at gmail dot com
2024-02-25 13:23 ` hjl.tools at gmail dot com
` (6 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: hjl.tools at gmail dot com @ 2024-02-25 13:12 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114097
H.J. Lu <hjl.tools at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Last reconfirmed| |2024-02-25
Version|unknown |14.0
CC| |hjl.tools at gmail dot com
Status|UNCONFIRMED |NEW
Ever confirmed|0 |1
--- Comment #1 from H.J. Lu <hjl.tools at gmail dot com> ---
__attribute__((noreturn)) works in GCC 14:
[hjl@gnu-cfl-3 tmp]$ cat y.c
#include<setjmp.h>
#include<stdio.h>
//_Noreturn
__attribute__((noreturn))
void noret(unsigned A, unsigned B, unsigned C, unsigned D, unsigned E, jmp_buf
Jb){
for(;A--;) puts("A");
for(;B--;) puts("B");
for(;C--;) puts("C");
for(;D--;) puts("D");
for(;E--;) puts("E");
longjmp(Jb,1);
}
[hjl@gnu-cfl-3 tmp]$ /usr/gcc-14.0.1-x32/bin/gcc -S -O2 y.c
[hjl@gnu-cfl-3 tmp]$ cat y.s
.file "y.c"
.text
.section .rodata.str1.1,"aMS",@progbits,1
.LC0:
.string "A"
.LC1:
.string "B"
.LC2:
.string "C"
.LC3:
.string "D"
.LC4:
.string "E"
.text
.p2align 4
.globl noret
.type noret, @function
noret:
.LFB11:
.cfi_startproc
subq $8, %rsp
.cfi_def_cfa_offset 16
movl %esi, %r15d
movl %edx, %r14d
movl %ecx, %r13d
movl %r8d, %ebp
movq %r9, %r12
testl %edi, %edi
je .L2
leal -1(%rdi), %ebx
.p2align 4,,10
.p2align 3
.L3:
movl $.LC0, %edi
call puts
subl $1, %ebx
jnb .L3
.L2:
leal -1(%r15), %ebx
testl %r15d, %r15d
je .L4
.p2align 4,,10
.p2align 3
.L5:
movl $.LC1, %edi
call puts
subl $1, %ebx
jnb .L5
.L4:
leal -1(%r14), %ebx
testl %r14d, %r14d
je .L6
.p2align 4,,10
.p2align 3
.L7:
movl $.LC2, %edi
call puts
subl $1, %ebx
jnb .L7
.L6:
leal -1(%r13), %ebx
testl %r13d, %r13d
je .L8
.p2align 4,,10
.p2align 3
.L9:
movl $.LC3, %edi
call puts
subl $1, %ebx
jnb .L9
.L8:
leal -1(%rbp), %ebx
testl %ebp, %ebp
je .L10
.p2align 4,,10
.p2align 3
.L11:
movl $.LC4, %edi
call puts
subl $1, %ebx
jnb .L11
.L10:
movl $1, %esi
movq %r12, %rdi
call longjmp
.cfi_endproc
.LFE11:
.size noret, .-noret
.ident "GCC: (GNU) 14.0.1 20240223 (experimental)"
.section .note.GNU-stack,"",@progbits
[hjl@gnu-cfl-3 tmp]$
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug c/114097] Missed register optimization in _Noreturn functions
2024-02-25 11:07 [Bug c/114097] New: Missed register optimization in _Noreturn functions pskocik at gmail dot com
2024-02-25 13:12 ` [Bug c/114097] " hjl.tools at gmail dot com
@ 2024-02-25 13:23 ` hjl.tools at gmail dot com
2024-02-25 13:37 ` hjl.tools at gmail dot com
` (5 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: hjl.tools at gmail dot com @ 2024-02-25 13:23 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114097
--- Comment #2 from H.J. Lu <hjl.tools at gmail dot com> ---
I couldn't find a way to access the _Noreturn info in backend.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug c/114097] Missed register optimization in _Noreturn functions
2024-02-25 11:07 [Bug c/114097] New: Missed register optimization in _Noreturn functions pskocik at gmail dot com
2024-02-25 13:12 ` [Bug c/114097] " hjl.tools at gmail dot com
2024-02-25 13:23 ` hjl.tools at gmail dot com
@ 2024-02-25 13:37 ` hjl.tools at gmail dot com
2024-02-25 13:42 ` [Bug target/114097] " hjl.tools at gmail dot com
` (4 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: hjl.tools at gmail dot com @ 2024-02-25 13:37 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114097
--- Comment #3 from H.J. Lu <hjl.tools at gmail dot com> ---
Created attachment 57524
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=57524&action=edit
A patch
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug target/114097] Missed register optimization in _Noreturn functions
2024-02-25 11:07 [Bug c/114097] New: Missed register optimization in _Noreturn functions pskocik at gmail dot com
` (2 preceding siblings ...)
2024-02-25 13:37 ` hjl.tools at gmail dot com
@ 2024-02-25 13:42 ` hjl.tools at gmail dot com
2024-02-25 14:18 ` pskocik at gmail dot com
` (3 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: hjl.tools at gmail dot com @ 2024-02-25 13:42 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114097
H.J. Lu <hjl.tools at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Component|c |target
Target Milestone|--- |14.0
Assignee|unassigned at gcc dot gnu.org |hjl.tools at gmail dot com
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug target/114097] Missed register optimization in _Noreturn functions
2024-02-25 11:07 [Bug c/114097] New: Missed register optimization in _Noreturn functions pskocik at gmail dot com
` (3 preceding siblings ...)
2024-02-25 13:42 ` [Bug target/114097] " hjl.tools at gmail dot com
@ 2024-02-25 14:18 ` pskocik at gmail dot com
2024-02-25 16:09 ` hjl.tools at gmail dot com
` (2 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: pskocik at gmail dot com @ 2024-02-25 14:18 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114097
--- Comment #4 from Petr Skocik <pskocik at gmail dot com> ---
Excellent! Thank you very much. Didn't realize the functionality was already
there, but didn't work without an explicit __attribute((noreturn)). Now I can
get rid of my most complex assembly function which I stupidly (back then I
thought cleverly) wrote. :)
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug target/114097] Missed register optimization in _Noreturn functions
2024-02-25 11:07 [Bug c/114097] New: Missed register optimization in _Noreturn functions pskocik at gmail dot com
` (4 preceding siblings ...)
2024-02-25 14:18 ` pskocik at gmail dot com
@ 2024-02-25 16:09 ` hjl.tools at gmail dot com
2024-02-26 10:31 ` cvs-commit at gcc dot gnu.org
2024-02-26 11:10 ` hjl.tools at gmail dot com
7 siblings, 0 replies; 9+ messages in thread
From: hjl.tools at gmail dot com @ 2024-02-25 16:09 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114097
--- Comment #5 from H.J. Lu <hjl.tools at gmail dot com> ---
A patch is submitted:
https://patchwork.sourceware.org/project/gcc/list/?series=31294
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug target/114097] Missed register optimization in _Noreturn functions
2024-02-25 11:07 [Bug c/114097] New: Missed register optimization in _Noreturn functions pskocik at gmail dot com
` (5 preceding siblings ...)
2024-02-25 16:09 ` hjl.tools at gmail dot com
@ 2024-02-26 10:31 ` cvs-commit at gcc dot gnu.org
2024-02-26 11:10 ` hjl.tools at gmail dot com
7 siblings, 0 replies; 9+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2024-02-26 10:31 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114097
--- Comment #6 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by H.J. Lu <hjl@gcc.gnu.org>:
https://gcc.gnu.org/g:bb98f71bac8aace4e685e648a81dfaf365123833
commit r14-9178-gbb98f71bac8aace4e685e648a81dfaf365123833
Author: H.J. Lu <hjl.tools@gmail.com>
Date: Sun Feb 25 13:14:39 2024 -0800
x86: Check interrupt instead of noreturn attribute
ix86_set_func_type checks noreturn attribute to avoid incompatible
attribute error in LTO1 on interrupt functions. Since TREE_THIS_VOLATILE
is set also for _Noreturn without noreturn attribute, check interrupt
attribute for interrupt functions instead.
gcc/
PR target/114097
* config/i386/i386-options.cc (ix86_set_func_type): Check
interrupt instead of noreturn attribute.
gcc/testsuite/
PR target/114097
* gcc.target/i386/pr114097-1.c: New test.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug target/114097] Missed register optimization in _Noreturn functions
2024-02-25 11:07 [Bug c/114097] New: Missed register optimization in _Noreturn functions pskocik at gmail dot com
` (6 preceding siblings ...)
2024-02-26 10:31 ` cvs-commit at gcc dot gnu.org
@ 2024-02-26 11:10 ` hjl.tools at gmail dot com
7 siblings, 0 replies; 9+ messages in thread
From: hjl.tools at gmail dot com @ 2024-02-26 11:10 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114097
H.J. Lu <hjl.tools at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|--- |FIXED
Status|NEW |RESOLVED
--- Comment #7 from H.J. Lu <hjl.tools at gmail dot com> ---
Fixed.
^ permalink raw reply [flat|nested] 9+ messages in thread
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2024-02-25 11:07 [Bug c/114097] New: Missed register optimization in _Noreturn functions pskocik at gmail dot com
2024-02-25 13:12 ` [Bug c/114097] " hjl.tools at gmail dot com
2024-02-25 13:23 ` hjl.tools at gmail dot com
2024-02-25 13:37 ` hjl.tools at gmail dot com
2024-02-25 13:42 ` [Bug target/114097] " hjl.tools at gmail dot com
2024-02-25 14:18 ` pskocik at gmail dot com
2024-02-25 16:09 ` hjl.tools at gmail dot com
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