[Bug target/36409] Additional instructions in prologue and epilogue.

[Bug target/36409] Additional instructions in prologue and epilogue.

[rearnsha at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=36409

Richard Earnshaw <rearnsha at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|2009-04-21 14:42:20         |2021-12-20

--- Comment #3 from Richard Earnshaw <rearnsha at gcc dot gnu.org> ---
Still a problem even today.
The 'optimized' gimple code is:

__attribute__((noinline))
void foo (struct Foo f)
{
  int * _1;

  <bb 2> [local count: 1073741824]:
  _1 = f.p;
  *_1 = 0;
  return;

}

which then gets expanded to copy the incoming argument to the stack

[Bug rtl-optimization/36409] New: Additional instructions in prologue and epilogue.

[ramana at icerasemi dot com]

Stack space creation instructions in prologue and epilogue don't get deleted. 

foo:
        sub     sp, sp, #8 --> Unnecessary 
        mov     r3, #0
        add     sp, sp, #8 --> Unnecessary
        str     r3, [r0]


struct Foo {
  int *p;
  int *q;
};

void __attribute__((noinline))
     foo(struct Foo f)
{
  *f.p = 0;
}


This appears to be due to get_frame_size returning the size of the incoming
parameters being 8 bytes in the backend .


-- 
           Summary: Additional instructions in prologue and epilogue.
           Product: gcc
           Version: 4.3.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: ramana at icerasemi dot com
  GCC host triplet: i686-linux
GCC target triplet: arm-none-eabi


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36409

[Bug target/36409] Additional instructions in prologue and epilogue.

[ramana dot r at gmail dot com]

------- Comment #1 from ramana dot r at gmail dot com  2009-02-04 23:38 -------
4.4.0 with revision id 143499 generates the following code with -O3 , -O2 and
-Os . The same code is generated for 4.3.3 as well 

        sub     sp, sp, #8
        mov     r3, sp
        mov     r2, #0
        stmia   r3, {r0, r1}
        str     r2, [r0, #0]
        add     sp, sp, #8
        bx      lr




Clearly things have gotten worse with an extra stmia being generated in this
case where the argument registers are being saved on the stack with the stmia
instruction. 


-- 

ramana dot r at gmail dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rearnsha at arm dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36409

[Bug target/36409] Additional instructions in prologue and epilogue.

[ramana at gcc dot gnu dot org]

------- Comment #2 from ramana at gcc dot gnu dot org  2009-04-21 14:42 -------
confirmed.


-- 

ramana at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2009-04-21 14:42:20
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36409