[Bug target/46470] New: "add $0x8,%rsp" no longer optimized to pop

[Bug target/46470] New: "add $0x8,%rsp" no longer optimized to pop

[hubicka at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46470

           Summary: "add    $0x8,%rsp" no longer optimized to pop
           Product: gcc
           Version: 4.5.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: hubicka@gcc.gnu.org


Created attachment 22390
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=22390
preprocessed testcase.

This is another cause of CSiBE regression at x86_64.

Mainline produces:

00000000000000f4 <yyerror>:
  f4:   48 83 ec 08             sub    $0x8,%rsp
  f8:   48 89 fa                mov    %rdi,%rdx
  fb:   48 8b 3d 00 00 00 00    mov    0x0(%rip),%rdi        # 102
<yyerror+0xe>
 102:   be 00 00 00 00          mov    $0x0,%esi
 107:   31 c0                   xor    %eax,%eax
 109:   e8 00 00 00 00          callq  10e <yyerror+0x1a>
 10e:   31 c0                   xor    %eax,%eax
 110:   48 83 c4 08             add    $0x8,%rsp
 114:   c3                      retq

GCC 4.3 produces:

  52:   48 83 ec 08             sub    $0x8,%rsp
  56:   48 89 fa                mov    %rdi,%rdx
  59:   48 8b 3d 00 00 00 00    mov    0x0(%rip),%rdi        # 60 <yyerror+0xe>
  60:   be 00 00 00 00          mov    $0x0,%esi
  65:   31 c0                   xor    %eax,%eax
  67:   e8 00 00 00 00          callq  6c <yyerror+0x1a>
  6c:   31 c0                   xor    %eax,%eax
  6e:   5a                      pop    %rdx
  6f:   c3                      retq

This is because CFA_ADJUST_CFA reg note is in the way now.
Richard, I think this is result of your changes, what would be best way to
handle this?  I guess peephole2 can just move the note when it translates one
intstruction to one instruction. This however breaks because we want to split
up to 3 pops when doing -Os.
I guess also the epilogue code can just emit the pops directly. There always
should be free register available at this time.

[Bug target/46470] "add $0x8,%rsp" no longer optimized to pop

[rth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46470

Richard Henderson <rth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2010.11.16 16:55:44
         AssignedTo|unassigned at gcc dot       |rth at gcc dot gnu.org
                   |gnu.org                     |
     Ever Confirmed|0                           |1

--- Comment #1 from Richard Henderson <rth at gcc dot gnu.org> 2010-11-16 16:55:44 UTC ---
Mine.

[Bug target/46470] "add $0x8,%rsp" no longer optimized to pop

[rth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46470

--- Comment #2 from Richard Henderson <rth at gcc dot gnu.org> 2010-11-16 22:22:19 UTC ---
Author: rth
Date: Tue Nov 16 22:22:13 2010
New Revision: 166829

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=166829
Log:
PR target/46470
        * recog.c (peep2_attempt): Convert frame-related info when possible.
        (peep2_fill_buffer): Allow frame-related insns into the buffer.
        (peephole2_optimize): Allow peep2_attempt to fail.

Added:
    trunk/gcc/testsuite/gcc.target/i386/pr46470.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/recog.c

[Bug target/46470] "add $0x8,%rsp" no longer optimized to pop

[rth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46470

Richard Henderson <rth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.6.0

--- Comment #3 from Richard Henderson <rth at gcc dot gnu.org> 2010-11-16 22:35:01 UTC ---
Fixed for mainline.