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* [Bug target/95783] New: Inefficient use of the stack when a function takes the address of its argument @ 2020-06-20 6:34 josephcsible at gmail dot com 2020-06-20 12:12 ` [Bug target/95783] " pinskia at gcc dot gnu.org ` (2 more replies) 0 siblings, 3 replies; 4+ messages in thread From: josephcsible at gmail dot com @ 2020-06-20 6:34 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95783 Bug ID: 95783 Summary: Inefficient use of the stack when a function takes the address of its argument Product: gcc Version: 10.1.0 Status: UNCONFIRMED Keywords: missed-optimization Severity: normal Priority: P3 Component: target Assignee: unassigned at gcc dot gnu.org Reporter: josephcsible at gmail dot com Target Milestone: --- Target: x86_64-linux-gnu Consider this C code: void g(long *); long f(long x) { g(&x); return x; } At either "-O3" or "-Os", it results in this assembly: f: subq $24, %rsp movq %rdi, 8(%rsp) leaq 8(%rsp), %rdi call g movq 8(%rsp), %rax addq $24, %rsp ret There are two problems with this: it's unnecessarily complicated with extra instructions, and it wastes 16 bytes of stack space. I'd rather see this assembly instead: f: pushq %rdi movq %rsp, %rdi call g popq %rax ret https://godbolt.org/z/PuNB6Y ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug target/95783] Inefficient use of the stack when a function takes the address of its argument 2020-06-20 6:34 [Bug target/95783] New: Inefficient use of the stack when a function takes the address of its argument josephcsible at gmail dot com @ 2020-06-20 12:12 ` pinskia at gcc dot gnu.org 2020-06-20 13:28 ` schwab@linux-m68k.org 2020-06-22 7:57 ` rguenth at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: pinskia at gcc dot gnu.org @ 2020-06-20 12:12 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95783 --- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> --- Note the stack is required to be 16 byte aligned so you need one more push. ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug target/95783] Inefficient use of the stack when a function takes the address of its argument 2020-06-20 6:34 [Bug target/95783] New: Inefficient use of the stack when a function takes the address of its argument josephcsible at gmail dot com 2020-06-20 12:12 ` [Bug target/95783] " pinskia at gcc dot gnu.org @ 2020-06-20 13:28 ` schwab@linux-m68k.org 2020-06-22 7:57 ` rguenth at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: schwab@linux-m68k.org @ 2020-06-20 13:28 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95783 --- Comment #2 from Andreas Schwab <schwab@linux-m68k.org> --- That is already handled through the return address push. ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug target/95783] Inefficient use of the stack when a function takes the address of its argument 2020-06-20 6:34 [Bug target/95783] New: Inefficient use of the stack when a function takes the address of its argument josephcsible at gmail dot com 2020-06-20 12:12 ` [Bug target/95783] " pinskia at gcc dot gnu.org 2020-06-20 13:28 ` schwab@linux-m68k.org @ 2020-06-22 7:57 ` rguenth at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: rguenth at gcc dot gnu.org @ 2020-06-22 7:57 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95783 Richard Biener <rguenth at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Ever confirmed|0 |1 Last reconfirmed| |2020-06-22 Status|UNCONFIRMED |NEW --- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> --- Confirmed. ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2020-06-22 7:57 UTC | newest] Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2020-06-20 6:34 [Bug target/95783] New: Inefficient use of the stack when a function takes the address of its argument josephcsible at gmail dot com 2020-06-20 12:12 ` [Bug target/95783] " pinskia at gcc dot gnu.org 2020-06-20 13:28 ` schwab@linux-m68k.org 2020-06-22 7:57 ` rguenth at gcc dot gnu.org
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