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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
end of thread, other threads:[~2024-03-01 7:15 UTC | newest] Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 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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