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* [Bug target/95941] New: Passing a struct by value wastes 16 bytes on the stack
@ 2020-06-27 16:44 josephcsible at gmail dot com
  2020-06-29 10:36 ` [Bug target/95941] " rguenth at gcc dot gnu.org
  0 siblings, 1 reply; 2+ messages in thread
From: josephcsible at gmail dot com @ 2020-06-27 16:44 UTC (permalink / raw)
  To: gcc-bugs

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95941

            Bug ID: 95941
           Summary: Passing a struct by value wastes 16 bytes on the stack
           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:

extern struct foo {
    long x, y, z;
} s;

void f(struct foo);

void g(void) {
    f(s);
}

At "-O3", it compiles to this:

g:
        subq    $16, %rsp
        pushq   s+16(%rip)
        pushq   s+8(%rip)
        pushq   s(%rip)
        call    f
        addq    $40, %rsp
        ret

There's no reason at all to use that extra 16 bytes of stack space. It should
have compiled to this instead:

g:
        pushq   s+16(%rip)
        pushq   s+8(%rip)
        pushq   s(%rip)
        call    f
        addq    $24, %rsp
        ret

^ permalink raw reply	[flat|nested] 2+ messages in thread
* [Bug target/95941] Passing a struct by value wastes 16 bytes on the stack
  2020-06-27 16:44 [Bug target/95941] New: Passing a struct by value wastes 16 bytes on the stack josephcsible at gmail dot com
@ 2020-06-29 10:36 ` rguenth at gcc dot gnu.org
  0 siblings, 0 replies; 2+ messages in thread
From: rguenth at gcc dot gnu.org @ 2020-06-29 10:36 UTC (permalink / raw)
  To: gcc-bugs

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95941

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2020-06-29
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed.  ISTR a very recent duplicate.

^ permalink raw reply	[flat|nested] 2+ messages in thread
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2020-06-27 16:44 [Bug target/95941] New: Passing a struct by value wastes 16 bytes on the stack josephcsible at gmail dot com
2020-06-29 10:36 ` [Bug target/95941] " rguenth at gcc dot gnu.org

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