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* [Bug inline-asm/101438] New: Compiler hang on inline asm with local register and VLA operands
@ 2021-07-13 14:36 andrey.vihrov at gmail dot com
2021-07-14 6:07 ` [Bug inline-asm/101438] " rguenth at gcc dot gnu.org
` (4 more replies)
0 siblings, 5 replies; 6+ messages in thread
From: andrey.vihrov at gmail dot com @ 2021-07-13 14:36 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101438
Bug ID: 101438
Summary: Compiler hang on inline asm with local register and
VLA operands
Product: gcc
Version: 11.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: inline-asm
Assignee: unassigned at gcc dot gnu.org
Reporter: andrey.vihrov at gmail dot com
Target Milestone: ---
Target: x86_64-pc-linux-gnu
Compiling this C source:
int main(void)
{
register long long rax __asm__("rax") = 0;
register long long rbx __asm__("rbx") = 0;
register long long rcx __asm__("rcx") = 0;
register long long rdx __asm__("rdx") = 0;
register long long rsi __asm__("rsi") = 0;
register long long rdi __asm__("rdi") = 0;
register long long r8 __asm__("r8") = 0;
register long long r9 __asm__("r9") = 0;
register long long r10 __asm__("r10") = 0;
register long long r11 __asm__("r11") = 0;
register long long r12 __asm__("r12") = 0;
register long long r13 __asm__("r13") = 0;
register long long r14 __asm__("r14") = 0;
register long long r15 __asm__("r15") = 0;
volatile int x = 1;
char arr[x];
__asm__ (""
:
: "r"(rax),
"r"(rbx),
"r"(rcx),
"r"(rdx),
"r"(rsi),
"r"(rdi),
"r"(r8),
"r"(r9),
"r"(r10),
"r"(r11),
"r"(r12),
"r"(r13),
"r"(r14),
"r"(r15),
"m"(arr)
);
}
with "gcc -O1 test.c" causes the compiler to hang in an infinite loop.
Note: This code could possibly be formally incorrect, as [1] warns about
potential clobbering after initialization of local register variables.
[1] https://gcc.gnu.org/onlinedocs/gcc/Local-Register-Variables.html
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug inline-asm/101438] Compiler hang on inline asm with local register and VLA operands
2021-07-13 14:36 [Bug inline-asm/101438] New: Compiler hang on inline asm with local register and VLA operands andrey.vihrov at gmail dot com
@ 2021-07-14 6:07 ` rguenth at gcc dot gnu.org
2021-07-14 18:26 ` pinskia at gcc dot gnu.org
` (3 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: rguenth at gcc dot gnu.org @ 2021-07-14 6:07 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101438
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |accepts-invalid,
| |compile-time-hog, ra
Status|UNCONFIRMED |NEW
Last reconfirmed| |2021-07-14
Ever confirmed|0 |1
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
At -O0 we get
t3.c: In function 'main':
t3.c:21:5: error: 'asm' operand has impossible constraints
21 | __asm__ (""
| ^~~~~~~
likely because there's not enough registers to pass in 'arr' (and we need a FP
to allocate arr). At -O1 it looks like we think we can manage but do not make
progress reloading.
So confirmed, a diagnostic would be nice.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug inline-asm/101438] Compiler hang on inline asm with local register and VLA operands
2021-07-13 14:36 [Bug inline-asm/101438] New: Compiler hang on inline asm with local register and VLA operands andrey.vihrov at gmail dot com
2021-07-14 6:07 ` [Bug inline-asm/101438] " rguenth at gcc dot gnu.org
@ 2021-07-14 18:26 ` pinskia at gcc dot gnu.org
2021-07-14 19:11 ` andrey.vihrov at gmail dot com
` (2 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-07-14 18:26 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101438
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
This code is almost definitely invalid:
"m"(arr)
You are asigning the array/pointer that the VLA is.
This is very much related to PR 71572 for similar reasons.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug inline-asm/101438] Compiler hang on inline asm with local register and VLA operands
2021-07-13 14:36 [Bug inline-asm/101438] New: Compiler hang on inline asm with local register and VLA operands andrey.vihrov at gmail dot com
2021-07-14 6:07 ` [Bug inline-asm/101438] " rguenth at gcc dot gnu.org
2021-07-14 18:26 ` pinskia at gcc dot gnu.org
@ 2021-07-14 19:11 ` andrey.vihrov at gmail dot com
2022-07-30 11:26 ` [Bug target/101438] Compiler hang on inline asm with local register and alloca andrey.vihrov at gmail dot com
2022-08-02 6:18 ` andrey.vihrov at gmail dot com
4 siblings, 0 replies; 6+ messages in thread
From: andrey.vihrov at gmail dot com @ 2021-07-14 19:11 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101438
--- Comment #3 from Andrey Vihrov <andrey.vihrov at gmail dot com> ---
Created attachment 51152
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=51152&action=edit
Alternative testcase using __builtin_alloca()
Thanks.
This code is the result of minimization. It seems that it is sufficient to make
inline asm depend on arr in any form.
"m"(arr[0]) (and initializing the array element) reproduces the issue as well.
I've also attached a similar testcase that compiles and runs at -O0, but hangs
the compiler at -O1 (and which likewise references the pointer itself with
"m").
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug target/101438] Compiler hang on inline asm with local register and alloca
2021-07-13 14:36 [Bug inline-asm/101438] New: Compiler hang on inline asm with local register and VLA operands andrey.vihrov at gmail dot com
` (2 preceding siblings ...)
2021-07-14 19:11 ` andrey.vihrov at gmail dot com
@ 2022-07-30 11:26 ` andrey.vihrov at gmail dot com
2022-08-02 6:18 ` andrey.vihrov at gmail dot com
4 siblings, 0 replies; 6+ messages in thread
From: andrey.vihrov at gmail dot com @ 2022-07-30 11:26 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101438
--- Comment #4 from Andrey Vihrov <andrey.vihrov at gmail dot com> ---
Looks like this is a duplicate of bug 105032 (or vice versa).
Both samples from this bug succeed for me with GCC 11.3 and GCC 12.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug target/101438] Compiler hang on inline asm with local register and alloca
2021-07-13 14:36 [Bug inline-asm/101438] New: Compiler hang on inline asm with local register and VLA operands andrey.vihrov at gmail dot com
` (3 preceding siblings ...)
2022-07-30 11:26 ` [Bug target/101438] Compiler hang on inline asm with local register and alloca andrey.vihrov at gmail dot com
@ 2022-08-02 6:18 ` andrey.vihrov at gmail dot com
4 siblings, 0 replies; 6+ messages in thread
From: andrey.vihrov at gmail dot com @ 2022-08-02 6:18 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101438
Andrey Vihrov <andrey.vihrov at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution|--- |DUPLICATE
--- Comment #5 from Andrey Vihrov <andrey.vihrov at gmail dot com> ---
Closing as a duplicate.
*** This bug has been marked as a duplicate of bug 105032 ***
^ permalink raw reply [flat|nested] 6+ messages in thread
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2021-07-13 14:36 [Bug inline-asm/101438] New: Compiler hang on inline asm with local register and VLA operands andrey.vihrov at gmail dot com
2021-07-14 6:07 ` [Bug inline-asm/101438] " rguenth at gcc dot gnu.org
2021-07-14 18:26 ` pinskia at gcc dot gnu.org
2021-07-14 19:11 ` andrey.vihrov at gmail dot com
2022-07-30 11:26 ` [Bug target/101438] Compiler hang on inline asm with local register and alloca andrey.vihrov at gmail dot com
2022-08-02 6:18 ` andrey.vihrov at gmail dot com
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