[Bug c++/110484] New: Spec2017 541 after adding the '-flto-fomit-frame-pointer' optimization, after optimizing the rnreg, directly replaced other registers with the $r22 register, so that the value of the $r22 register was destroyed without being saved.

[Bug c++/110484] New: Spec2017 541 after adding the '-flto-fomit-frame-pointer' optimization, after optimizing the rnreg, directly replaced other registers with the $r22 register, so that the value of the $r22 register was destroyed without being saved.

[chenglulu at loongson dot cn]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110484

            Bug ID: 110484
           Summary: Spec2017 541 after adding the
                    '-flto-fomit-frame-pointer' optimization, after
                    optimizing the rnreg, directly replaced other
                    registers with the $r22 register, so that the value of
                    the $r22 register was destroyed without being saved.
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: chenglulu at loongson dot cn
  Target Milestone: ---
            Target: loongarch64-*-linux

Spec2017 541 after adding the '-flto-fomit-frame-pointer' optimization, after
optimizing the rnreg, directly replaced other registers with the $r22 register,
so that the value of the $r22 register was destroyed without being saved.

Through debugging, it was found that when compiling the SGFTree .cpp file, the
load_from_file function generated the following template in pro_and_epilogue
optimization:
(insn 782 781 783 61 (set (mem:BLK (scratch) [0  A8])
        (unspec:BLK [
                (reg/f:DI 3 $r3)
                (reg/f:DI 22 $r22)
            ] UNSPEC_TIE)) "SGFTree.cpp":115:1 -1
     (nil))
This results in $r22 being present in the load_from_file's reg ever live list
thereafter.　However, this is not desirable when the $r22 register is not used
in the function.

[Bug c++/110484] Spec2017 541 after adding the '-flto-fomit-frame-pointer' optimization, after optimizing the rnreg, directly replaced other registers with the $r22 register, so that the value of the $r22 register was destroyed without being saved.

[chenglulu at loongson dot cn]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110484

--- Comment #1 from chenglulu <chenglulu at loongson dot cn> ---

The following code modification problem can be solved：

--- a/gcc/config/loongarch/loongarch.cc
+++ b/gcc/config/loongarch/loongarch.cc
@@ -1112,7 +1112,9 @@ loongarch_first_stack_step (struct loongarch_frame_info
*frame)
 static void
 loongarch_emit_stack_tie (void)
 {
-  emit_insn (gen_stack_tie (Pmode, stack_pointer_rtx,
hard_frame_pointer_rtx));
+  emit_insn (gen_stack_tie (Pmode, stack_pointer_rtx,
+                           frame_pointer_needed ? hard_frame_pointer_rtx
+                           : stack_pointer_rtx));
 }

[Bug c++/110484] Spec2017 541 after adding the '-flto-fomit-frame-pointer' optimization, after optimizing the rnreg, directly replaced other registers with the $r22 register, so that the value of the $r22 register was destroyed without being saved.

[xry111 at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110484

Xi Ruoyao <xry111 at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |xry111 at gcc dot gnu.org

--- Comment #2 from Xi Ruoyao <xry111 at gcc dot gnu.org> ---
Hmm, I don't quite get the problem.  r22 is a saved register, so if it's
clobbered w/o being saved, the issue will be a wrong-code, instead of a
missed-optimization?

[Bug target/110484] Spec2017 541 after adding the '-flto-fomit-frame-pointer' optimization, after optimizing the rnreg, directly replaced other registers with the $r22 register, so that the value of the $r22 register was destroyed without being saved.

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110484

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by LuluCheng <chenglulu@gcc.gnu.org>:

https://gcc.gnu.org/g:1967f21d000e09d3d3190317af7923b578ce02b1

commit r14-3605-g1967f21d000e09d3d3190317af7923b578ce02b1
Author: Lulu Cheng <chenglulu@loongson.cn>
Date:   Thu Jun 29 19:30:59 2023 +0800

    LoongArch: Fix bug in loongarch_emit_stack_tie [PR110484].

    Which may result in implicit references to $fp when frame_pointer_needed is
false,
    causing regs_ever_live[$fp] to be true when $fp is not explicitly used,
    resulting in $fp being used as the target replacement register in the rnreg
pass.

    The bug originates from SPEC2017 541.leela_r(-flto).

    gcc/ChangeLog:

            PR target/110484
            * config/loongarch/loongarch.cc (loongarch_emit_stack_tie): Use the
            frame_pointer_needed to determine whether to use the $fp register.

    Co-authored-by: Guo Jie <guojie@loongson.cn>

[Bug target/110484] Spec2017 541 after adding the '-flto-fomit-frame-pointer' optimization, after optimizing the rnreg, directly replaced other registers with the $r22 register, so that the value of the $r22 register was destroyed without being saved.

[chenglulu at loongson dot cn]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110484

chenglulu <chenglulu at loongson dot cn> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #4 from chenglulu <chenglulu at loongson dot cn> ---
resolved

[Bug target/110484] Spec2017 541 after adding the '-flto-fomit-frame-pointer' optimization, after optimizing the rnreg, directly replaced other registers with the $r22 register, so that the value of the $r22 register was destroyed without being saved.

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110484

--- Comment #5 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-13 branch has been updated by LuluCheng
<chenglulu@gcc.gnu.org>:

https://gcc.gnu.org/g:3f23fa7e74fa01828d649e8ee7230701b6fb1e19

commit r13-7773-g3f23fa7e74fa01828d649e8ee7230701b6fb1e19
Author: Lulu Cheng <chenglulu@loongson.cn>
Date:   Thu Jun 29 19:30:59 2023 +0800

    LoongArch: Fix bug in loongarch_emit_stack_tie [PR110484].

    Which may result in implicit references to $fp when frame_pointer_needed is
false,
    causing regs_ever_live[$fp] to be true when $fp is not explicitly used,
    resulting in $fp being used as the target replacement register in the rnreg
pass.

    The bug originates from SPEC2017 541.leela_r(-flto).

    gcc/ChangeLog:

            PR target/110484
            * config/loongarch/loongarch.cc (loongarch_emit_stack_tie): Use the
            frame_pointer_needed to determine whether to use the $fp register.

    Co-authored-by: Guo Jie <guojie@loongson.cn>

    (cherry picked from commit 1967f21d000e09d3d3190317af7923b578ce02b1)

[Bug target/110484] Spec2017 541 after adding the '-flto-fomit-frame-pointer' optimization, after optimizing the rnreg, directly replaced other registers with the $r22 register, so that the value of the $r22 register was destroyed without being saved.

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110484

--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-12 branch has been updated by LuluCheng
<chenglulu@gcc.gnu.org>:

https://gcc.gnu.org/g:d60c00492eb5818493560f299f06d1e3d9efcc69

commit r12-9840-gd60c00492eb5818493560f299f06d1e3d9efcc69
Author: Lulu Cheng <chenglulu@loongson.cn>
Date:   Thu Jun 29 19:30:59 2023 +0800

    LoongArch: Fix bug in loongarch_emit_stack_tie [PR110484].

    Which may result in implicit references to $fp when frame_pointer_needed is
false,
    causing regs_ever_live[$fp] to be true when $fp is not explicitly used,
    resulting in $fp being used as the target replacement register in the rnreg
pass.

    The bug originates from SPEC2017 541.leela_r(-flto).

    gcc/ChangeLog:

            PR target/110484
            * config/loongarch/loongarch.cc (loongarch_emit_stack_tie): Use the
            frame_pointer_needed to determine whether to use the $fp register.

    Co-authored-by: Guo Jie <guojie@loongson.cn>

    (cherry picked from commit 1967f21d000e09d3d3190317af7923b578ce02b1)