[Bug rtl-optimization/63718] New: ARM Thumb1 bootstrap fail after fuse-caller-save info in cprop-hardreg

[Bug rtl-optimization/63718] New: ARM Thumb1 bootstrap fail after fuse-caller-save info in cprop-hardreg

[joey.ye at arm dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63718

            Bug ID: 63718
           Summary: ARM Thumb1 bootstrap fail after fuse-caller-save info
                    in cprop-hardreg
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: joey.ye at arm dot com

architecture option: --with-arch=armv4t --with-mode=thumb
BOOT_CFLAGS="-O2 -g"

(Stage2) Error message:
src/gcc/trunk/libgcc/libgcc2.c: In function ‘__mulvdi3’:
src/gcc/trunk/libgcc/libgcc2.h:209:20: internal compiler error: Segmentation
fault

First bad version: trunk@216365
Date:   Fri Oct 17 06:36:45 2014 +0000

    Use fuse-caller-save info in cprop-hardreg

    2014-10-17  Tom de Vries  <tom@codesourcery.com>

        PR rtl-optimization/61605
        * regcprop.c (copyprop_hardreg_forward_1): Use
        regs_invalidated_by_this_call instead of regs_invalidated_by_call.

        * gcc.target/i386/fuse-caller-save.c: Update addition check.  Add movl
        absence check.
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From: "joey.ye at arm dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/63718] ARM Thumb1 bootstrap fail after fuse-caller-save info in cprop-hardreg
Date: Mon, 03 Nov 2014 08:13:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idc718

--- Comment #1 from Joey Ye <joey.ye at arm dot com> ---
Challenging to reduce a small case, as inlining impacts optimization behavior.
Trying to describe the problem as clear as possible.

Problemetic generated code:
        mov     r0, r10
        mov     r1, r3
        mov     r2, r8
        str     r3, [sp, #8]
        bl      _ZL17bmp_iter_set_init
        mov     r3, r9
        ldr     r4, [r0, #12]   <--- r0 is used after call, which is clobbered
implicitly

_ZL17bmp_iter_set_init:
        ...
        pop     {r4}
        pop     {r0}     <--- clobbering r0, which is implicit from RTL view
        bx      r0

Prototype of bmp_iter_set_init:
static inline void  <--- return void
bmp_iter_set_init (bitmap_iterator *bi, const_bitmap map,
                   unsigned start_bit, unsigned *bit_no)

1. thumb1 (arch=armv4t) sometimes clobbers r0-r3 on return, with logic in
arm.c:thumb_exit

2. Behavior in 1 is implicit to RTL. A typical thumb1 return RTL will be
(jump_insn (unspec_volatile [
            (return)
        ] VUNSPEC_EPILOGUE))

3. Other RTLs in caller do not modifies all r0-r3

4. After 216365 copyprop_hardreg_forward_1 believes r0-r3 are not clobbered
during call. Bang!

Attached reduced RTL dump of cprop_hardreg and the previous pass.

[Bug rtl-optimization/63718] ARM Thumb1 bootstrap fail after fuse-caller-save info in cprop-hardreg

[joey.ye at arm dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63718

--- Comment #2 from Joey Ye <joey.ye at arm dot com> ---
Created attachment 33871
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=33871&action=edit
Reduced rtl dump

[Bug rtl-optimization/63718] ARM Thumb1 bootstrap fail after fuse-caller-save info in cprop-hardreg

[joey.ye at arm dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63718

--- Comment #3 from Joey Ye <joey.ye at arm dot com> ---
Created attachment 33872
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=33872&action=edit
Reduced rtl dump previous pass

[Bug rtl-optimization/63718] ARM Thumb1 bootstrap fail after fuse-caller-save info in cprop-hardreg

[joey.ye at arm dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63718

--- Comment #4 from Joey Ye <joey.ye at arm dot com> ---
Created attachment 33873
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=33873&action=edit
Preprocessed testcase

Options to reproduce:
-march=armv4t -mthumb -O2

[Bug rtl-optimization/63718] [5 Regression] ARM Thumb1 bootstrap fail after fuse-caller-save info in cprop-hardreg

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63718

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Target|                            |arm
   Target Milestone|---                         |5.0
            Summary|ARM Thumb1 bootstrap fail   |[5 Regression] ARM Thumb1
                   |after fuse-caller-save info |bootstrap fail after
                   |in cprop-hardreg            |fuse-caller-save info in
                   |                            |cprop-hardreg

[Bug rtl-optimization/63718] [5 Regression] ARM Thumb1 bootstrap fail after fuse-caller-save info in cprop-hardreg

[vries at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63718

vries at gcc dot gnu.org changed:

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

--- Comment #5 from vries at gcc dot gnu.org ---
Created attachment 33874
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=33874&action=edit
tentative patch, adds missing clobbers

Joey,

thanks for doing the analysis and the clear bug report. I cannot formally
confirm at this point since I don't have an arm bootstrap setup, but I agree,
those missing clobbers (while not causing problems otherwise) will cause
problems with fuse-caller-save.

I'd say the fix is to add the missing clobbers. Attached tentative patch
implements that fix.

Using the patch, I build a c-only arm compiler, compiled an example with
-mthumb and -march=armv4t and observed the new clobbers on the return in the
final dump:
...
(jump_insn 19 18 20 (parallel [
            (unspec_volatile [
                    (return)
            ] VUNSPEC_EPILOGUE)
            (clobber (reg:SI 0 r0))
            (clobber (reg:SI 1 r1))
            (clobber (reg:SI 2 r2))
            (clobber (reg:SI 3 r3))
        ]) test.c:9 773 {*epilogue_insns}
     (expr_list:REG_UNUSED (reg:SI 3 r3)
        (expr_list:REG_UNUSED (reg:SI 2 r2)
            (expr_list:REG_UNUSED (reg:SI 1 r1)
                (nil))))
 -> return)
...

Could you try out the patch and see if it fixes things for you?

Thanks,
- Tom

[Bug rtl-optimization/63718] [5 Regression] ARM Thumb1 bootstrap fail after fuse-caller-save info in cprop-hardreg

[joey.ye at arm dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63718

--- Comment #6 from Joey Ye <joey.ye at arm dot com> ---
(In reply to vries from comment #5)
> Could you try out the patch and see if it fixes things for you?
> 
Tom, thanks for the quick action. Apparantly this patch should recover the
bootstrap. I will test it and come back to you (bootstraping thumb1 with qemu
takes hours!)

However, I think the fix is too conservative. There are plenty of chances that
r0-r3 will not be clobbered by return. For example armv6-m will pretty much
never uses r0-r3 implicitly.

[Bug rtl-optimization/63718] [5 Regression] ARM Thumb1 bootstrap fail after fuse-caller-save info in cprop-hardreg

[joey.ye at arm dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63718

--- Comment #8 from Joey Ye <joey.ye at arm dot com> ---
(In reply to vries from comment #5)
> Created attachment 33874 [details]
> tentative patch, adds missing clobbers
This patch does recover thumb1 bootstrap

- Joey

[Bug rtl-optimization/63718] [5 Regression] ARM Thumb1 bootstrap fail after fuse-caller-save info in cprop-hardreg

[joey.ye at arm dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63718

--- Comment #9 from Joey Ye <joey.ye at arm dot com> ---
> 
> Indeed, the patch is conservative, but that's not such a bad idea for a
> correctness fix. We can always folllow up with a more optimal patch.
Tom, are you going to submit this patch for review, or are you working on a
more optimal one? Better to have this conservative patch to recover the
bootstrap first.

- Joey

[Bug rtl-optimization/63718] [5 Regression] ARM Thumb1 bootstrap fail after fuse-caller-save info in cprop-hardreg

[vries at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63718

--- Comment #10 from vries at gcc dot gnu.org ---
> Tom, are you going to submit this patch for review

I was planning to put this patch through build & regtest and submit, but next
week. Unfortunately I don't have time until then, I'm trying to submit
something else before stage1 closes.

[Bug rtl-optimization/63718] [5 Regression] ARM Thumb1 bootstrap fail after fuse-caller-save info in cprop-hardreg

[vries at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63718

--- Comment #11 from vries at gcc dot gnu.org ---
reproduced with r217718

[Bug rtl-optimization/63718] [5 Regression] ARM Thumb1 bootstrap fail after fuse-caller-save info in cprop-hardreg

[vries at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63718

--- Comment #12 from vries at gcc dot gnu.org ---
> reproduced with r217718

Sorry, wrong PR

[Bug rtl-optimization/63718] [5 Regression] ARM Thumb1 bootstrap fail after fuse-caller-save info in cprop-hardreg

[vries at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63718

--- Comment #13 from vries at gcc dot gnu.org ---
> I was planning to put this patch through build & regtest

Testing reveals: The r0 clobber is _not_ a good idea if the function has a
result ... Ouch.

[Bug rtl-optimization/63718] [5 Regression] ARM Thumb1 bootstrap fail after fuse-caller-save info in cprop-hardreg

[joey.ye at arm dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63718

--- Comment #14 from Joey Ye <joey.ye at arm dot com> ---
Em. Probably a more favorable solution is fix expand_epilogue to precisely
elaborate the side effect?

[Bug rtl-optimization/63718] [5 Regression] ARM Thumb1 bootstrap fail after fuse-caller-save info in cprop-hardreg

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63718

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code
           Priority|P3                          |P1

[Bug rtl-optimization/63718] [5 Regression] ARM Thumb1 bootstrap fail after fuse-caller-save info in cprop-hardreg

[vries at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63718

vries at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |patch

--- Comment #15 from vries at gcc dot gnu.org ---
https://gcc.gnu.org/ml/gcc-patches/2014-11/msg02648.html

[Bug rtl-optimization/63718] [5 Regression] ARM Thumb1 bootstrap fail after fuse-caller-save info in cprop-hardreg

[joey.ye at arm dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63718

Joey Ye <joey.ye at arm dot com> changed:

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

--- Comment #17 from Joey Ye <joey.ye at arm dot com> ---
Resolved in 218271, which is a work around. A new PR is expected to open for a
complete solution.

[Bug rtl-optimization/63718] [5 Regression] ARM Thumb1 bootstrap fail after fuse-caller-save info in cprop-hardreg

[vries at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63718

--- Comment #18 from vries at gcc dot gnu.org ---
(In reply to Joey Ye from comment #17)
> A new PR is expected to open for
> a complete solution.

PR 64154 - enable fuse-caller-save for Thumb1