[Bug debug/103351] New: [12 Regression] '-fcompare-debug' failure (length) at -O2

[Bug debug/103351] New: [12 Regression] '-fcompare-debug' failure (length) at -O2

[zsojka at seznam dot cz]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103351

            Bug ID: 103351
           Summary: [12 Regression] '-fcompare-debug' failure (length) at
                    -O2
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Keywords: ice-on-valid-code
          Severity: normal
          Priority: P3
         Component: debug
          Assignee: unassigned at gcc dot gnu.org
          Reporter: zsojka at seznam dot cz
                CC: aoliva at gcc dot gnu.org
  Target Milestone: ---
              Host: x86_64-pc-linux-gnu

Created attachment 51845
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=51845&action=edit
auto-reduced testcase

Compiler output:
$ x86_64-pc-linux-gnu-g++ -O2 -fcompare-debug testcase.C -save-temps
x86_64-pc-linux-gnu-g++: error: testcase.C: '-fcompare-debug' failure (length)

$ x86_64-pc-linux-gnu-g++ -v
Using built-in specs.
COLLECT_GCC=/repo/gcc-trunk/binary-latest/bin/x86_64-pc-linux-gnu-g++
COLLECT_LTO_WRAPPER=/repo/gcc-trunk/binary-trunk-r12-5437-20211121132234-g09a4ffb72aa-checking-yes-rtl-df-extra-amd64/bin/../libexec/gcc/x86_64-pc-linux-gnu/12.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /repo/gcc-trunk//configure --enable-languages=c,c++
--enable-valgrind-annotations --disable-nls --enable-checking=yes,rtl,df,extra
--with-cloog --with-ppl --with-isl --build=x86_64-pc-linux-gnu
--host=x86_64-pc-linux-gnu --target=x86_64-pc-linux-gnu
--with-ld=/usr/bin/x86_64-pc-linux-gnu-ld
--with-as=/usr/bin/x86_64-pc-linux-gnu-as --disable-libstdcxx-pch
--prefix=/repo/gcc-trunk//binary-trunk-r12-5437-20211121132234-g09a4ffb72aa-checking-yes-rtl-df-extra-amd64
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 12.0.0 20211121 (experimental) (GCC)

[Bug tree-optimization/103351] [12 Regression] '-fcompare-debug' failure (length) at -O2

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103351

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2021-11-21
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
   Target Milestone|---                         |12.0

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed, the first (major) difference shows up in 199t.cddce3.



   if (&__str._M_local_buf == _13)
     goto <bb 4>; [30.00%]
   else
-    goto <bb 7>; [70.00%]
+    goto <bb 6>; [70.00%]

   <bb 4> [local count: 286689070]:
   _1 = &_10->D.4203.name;
   if (_1 != __trans_tmp_1_14(D))
-    goto <bb 6>; [90.00%]
+    goto <bb 5>; [90.00%]
   else
-    goto <bb 5>; [10.00%]
-
-  <bb 5> [local count: 28668907]:
-  goto <bb 9>; [100.00%]
+    goto <bb 8>; [10.00%]

-  <bb 6> [local count: 258020162]:
+  <bb 5> [local count: 258020162]:
   Trans_NS___cxx11_basic_string<char>::size (_1);
   pretmp_16 = __str._M_dataplus._M_p;
   goto <bb 9>; [100.00%]

-  <bb 7> [local count: 668941172]:
+  <bb 6> [local count: 668941172]:
   if (__trans_tmp_2_18(D) != 0)
-    goto <bb 8>; [50.00%]
+    goto <bb 7>; [50.00%]
   else
     goto <bb 9>; [50.00%]

-  <bb 8> [local count: 334470586]:
-  # DEBUG this => &__str
-  # DEBUG __p => &__str._M_local_buf
-  # DEBUG INLINE_ENTRY _M_data
+  <bb 7> [local count: 334470586]:
   __str._M_dataplus._M_p = &__str._M_local_buf;
-  goto <bb 5>; [100.00%]
+
+  <bb 8> [local count: 334470586]:

[Bug tree-optimization/103351] [12 Regression] '-fcompare-debug' failure (length) at -O2

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103351

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #1)
> Confirmed, the first (major) difference shows up in 199t.cddce3.

So maybe introduced by r12-5301.

[Bug tree-optimization/103351] [12 Regression] '-fcompare-debug' failure (length) at -O2 since r12-5301-g045206450386bcd7

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103351

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |marxin at gcc dot gnu.org,
                   |                            |rguenth at gcc dot gnu.org
            Summary|[12 Regression]             |[12 Regression]
                   |'-fcompare-debug' failure   |'-fcompare-debug' failure
                   |(length) at -O2             |(length) at -O2 since
                   |                            |r12-5301-g045206450386bcd7

--- Comment #3 from Martin Liška <marxin at gcc dot gnu.org> ---
Started with r12-5301-g045206450386bcd7.

[Bug tree-optimization/103351] [12 Regression] '-fcompare-debug' failure (length) at -O2 since r12-5301-g045206450386bcd7

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103351

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at gcc dot gnu.org      |rguenth at gcc dot gnu.org
             Status|NEW                         |ASSIGNED

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
I will have a look.

[Bug tree-optimization/103351] [12 Regression] '-fcompare-debug' failure (length) at -O2 since r12-5301-g045206450386bcd7

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103351

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
So the issue is that iterative_hash_expr of &__str._M_local_buf is not the
same for -g vs. -g0 which results in different ordering of the vector of
PHI arguments in sorted form.  First there's missing ordering we can use
based on ->dest_idx which should stabilize the sort somewhat.  But then
it might still be that we end up with different basic-block numbers when
there are two clusters of same PHI args and thus two forwarders to be
generated.

In the end this is because we hash in DECL_UID which are not the same here
(2872 vs 2873) which is OK.  So for the latter issue not exposed in this
testcase we should order clusters after the first ->dest_idx for example.
Though I'm not sure it is an isssue (but it could also improve stability
of testcases when reducing).  I'll try to fixup piecewise.

[Bug tree-optimization/103351] [12 Regression] '-fcompare-debug' failure (length) at -O2 since r12-5301-g045206450386bcd7

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103351

--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Richard Biener <rguenth@gcc.gnu.org>:

https://gcc.gnu.org/g:f456eaf2e0fb3ceb51c641fd348429bf59d215a9

commit r12-5447-gf456eaf2e0fb3ceb51c641fd348429bf59d215a9
Author: Richard Biener <rguenther@suse.de>
Date:   Mon Nov 22 11:23:55 2021 +0100

    tree-optimization/103351 - avoid compare-debug issue wrt CD-DCE change

    This avoids differences in the split edge of a cluster due to different
    order of same key PHI args when sorting by sorting after the edge
    destination index as second key.

    2021-11-22  Richard Biener  <rguenther@suse.de>

            PR tree-optimization/103351
            * tree-ssa-dce.c (sort_phi_args): Sort after e->dest_idx as
            second key.

            * g++.dg/torture/pr103351.C: New testcase.

[Bug tree-optimization/103351] [12 Regression] '-fcompare-debug' failure (length) at -O2 since r12-5301-g045206450386bcd7

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103351

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

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

--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> ---
Fixed.