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* [Bug middle-end/114185] New: Missed tail-call optimization due to an argument whose address is taken
@ 2024-03-01 6:25 dizhao at os dot amperecomputing.com
2024-03-01 6:28 ` [Bug middle-end/114185] " pinskia at gcc dot gnu.org
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: dizhao at os dot amperecomputing.com @ 2024-03-01 6:25 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114185
Bug ID: 114185
Summary: Missed tail-call optimization due to an argument whose
address is taken
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: dizhao at os dot amperecomputing.com
Target Milestone: ---
GCC (with "-Ofast") doesn't perform tail call optimization on a function like:
long test_func (long n, unsigned long u64arg,
unsigned int u32arg, unsigned long *p)
{
if (n > 0)
return test_func (n - 1, u64arg + (unsigned long) u32arg, u32arg, p);
else
return &u64arg - p;
}
llvm can optimize the tail call.
GCC gave up tail call optimization, because the following check in
find_tail_calls() failed on argument "u64arg":
/* The parameter should be a real operand, so that phi node
created for it at the start of the function has the meaning
of copying the value. This test implies is_gimple_reg_type
from the previous condition, however this one could be
relaxed by being more careful with copying the new value
of the parameter (emitting appropriate GIMPLE_ASSIGN and
updating the virtual operands). */
if (!is_gimple_reg (param))
break;
The check was to fix this ICE:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93487 . But in this case,
"&u64arg" won't be used in PHI argument, so it seems ok for tail call
optimization. (BTW, I tried current GCC trunk on the example code in PR 93487,
but haven't encounter the ICE with that check removed, because the PHI
arguments are "&y" and "&x" now.)
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug middle-end/114185] Missed tail-call optimization due to an argument whose address is taken
2024-03-01 6:25 [Bug middle-end/114185] New: Missed tail-call optimization due to an argument whose address is taken dizhao at os dot amperecomputing.com
@ 2024-03-01 6:28 ` pinskia at gcc dot gnu.org
2024-03-01 6:31 ` pinskia at gcc dot gnu.org
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: pinskia at gcc dot gnu.org @ 2024-03-01 6:28 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114185
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
This code is undefined if the if is not taken.
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug middle-end/114185] Missed tail-call optimization due to an argument whose address is taken
2024-03-01 6:25 [Bug middle-end/114185] New: Missed tail-call optimization due to an argument whose address is taken dizhao at os dot amperecomputing.com
2024-03-01 6:28 ` [Bug middle-end/114185] " pinskia at gcc dot gnu.org
@ 2024-03-01 6:31 ` pinskia at gcc dot gnu.org
2024-03-01 7:08 ` dizhao at os dot amperecomputing.com
2024-03-01 7:15 ` rguenth at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: pinskia at gcc dot gnu.org @ 2024-03-01 6:31 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114185
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Also the PR # you gave is wrong.
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug middle-end/114185] Missed tail-call optimization due to an argument whose address is taken
2024-03-01 6:25 [Bug middle-end/114185] New: Missed tail-call optimization due to an argument whose address is taken dizhao at os dot amperecomputing.com
2024-03-01 6:28 ` [Bug middle-end/114185] " pinskia at gcc dot gnu.org
2024-03-01 6:31 ` pinskia at gcc dot gnu.org
@ 2024-03-01 7:08 ` dizhao at os dot amperecomputing.com
2024-03-01 7:15 ` rguenth at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: dizhao at os dot amperecomputing.com @ 2024-03-01 7:08 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114185
--- Comment #3 from Di Zhao <dizhao at os dot amperecomputing.com> ---
Sorry, the old tracker for the code is PR 17749 .
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug middle-end/114185] Missed tail-call optimization due to an argument whose address is taken
2024-03-01 6:25 [Bug middle-end/114185] New: Missed tail-call optimization due to an argument whose address is taken dizhao at os dot amperecomputing.com
` (2 preceding siblings ...)
2024-03-01 7:08 ` dizhao at os dot amperecomputing.com
@ 2024-03-01 7:15 ` rguenth at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: rguenth at gcc dot gnu.org @ 2024-03-01 7:15 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114185
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |missed-optimization
--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
The tail recursion optimization doesn't support non-register argument passing.
Of course the example is also broken as Andrew says.
A "better" example might be taking the address with like
asm ("":: "g" (&u64arg));
Better make it meaningfully do sth with no invisible side-effects or escaping
of the address.
We should be pretty good these days with not setting TREE_ADDRESSABLE
unnecessarily (but I guess DECL_NOT_GIMPLE_REG should also inhibit
tail-recursion).
^ permalink raw reply [flat|nested] 5+ messages in thread
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2024-03-01 6:25 [Bug middle-end/114185] New: Missed tail-call optimization due to an argument whose address is taken dizhao at os dot amperecomputing.com
2024-03-01 6:28 ` [Bug middle-end/114185] " pinskia at gcc dot gnu.org
2024-03-01 6:31 ` pinskia at gcc dot gnu.org
2024-03-01 7:08 ` dizhao at os dot amperecomputing.com
2024-03-01 7:15 ` rguenth at gcc dot gnu.org
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