[Bug target/63354] New: -pg -mprofile-kernel creates unused stack frames on leaf functions on ppc64le

[Bug target/63354] New: -pg -mprofile-kernel creates unused stack frames on leaf functions on ppc64le

[anton at samba dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63354

            Bug ID: 63354
           Summary: -pg -mprofile-kernel creates unused stack frames on
                    leaf functions on ppc64le
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: anton at samba dot org

The following testcase:

int foo(void)
{
    return 1;
}

compiled with:

gcc -O2 -pg -mprofile-kernel -S foo.c

produces an unused stack frame:

foo:
    mflr 0
    std 0,16(1)
    bl _mcount
    mflr 0
    li 3,1
    std 0,16(1)
    stdu 1,-32(1)
    addi 1,1,32
    ori 2,2,0
    ld 0,16(1)
    mtlr 0
    blr

Note that older gcc versions allowed -mprofile-kernel to used on its own. While
there are issues with that (eg ignoring attribute no_instrument_function), it
does show the expected behaviour:

gcc -O2 -mprofile-kernel -S foo.c

foo:
    mflr 0
    std 0,16(1)
    bl _mcount
    li 3,1
    blr

So it seems to be something to do with -pg.

[Bug target/63354] gcc -pg -mprofile-kernel creates unused stack frames on leaf functions on ppc64le

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63354

Segher Boessenkool <segher at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Target|powerpc64le-linux           |powerpc*-*-*
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2014-09-24
                 CC|                            |segher at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #1 from Segher Boessenkool <segher at gcc dot gnu.org> ---
Confirmed.  We need
#define TARGET_KEEP_LEAF_WHEN_PROFILED hook_bool_void_true
to have it behave as you want.

[Bug target/63354] gcc -pg -mprofile-kernel creates unused stack frames on leaf functions on ppc64le

[anton at samba dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63354

--- Comment #2 from Anton Blanchard <anton at samba dot org> ---
Created attachment 33555
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=33555&action=edit
Avoid an unused stack frame for -mprofile-kernel  profiling on leaf functions.

[Bug target/63354] gcc -pg -mprofile-kernel creates unused stack frames on leaf functions on ppc64le

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63354

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |msebor at gcc dot gnu.org

--- Comment #3 from Martin Sebor <msebor at gcc dot gnu.org> ---
The attached patch still fixes the problem.  Anton, would you like to submit
the patch to gcc-patches?