[Bug debug/94618] New: [10 Regression] '-fcompare-debug' failure (length) with -O2 -fnon-call-exceptions

[Bug debug/94618] New: [10 Regression] '-fcompare-debug' failure (length) with -O2 -fnon-call-exceptions

[zsojka at seznam dot cz]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94618

            Bug ID: 94618
           Summary: [10 Regression] '-fcompare-debug' failure (length)
                    with -O2 -fnon-call-exceptions
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: debug
          Assignee: unassigned at gcc dot gnu.org
          Reporter: zsojka at seznam dot cz
  Target Milestone: ---
              Host: x86_64-pc-linux-gnu

Created attachment 48289
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=48289&action=edit
reduced testcase

Compiler output:
$ x86_64-pc-linux-gnu-g++ -O2 -fnon-call-exceptions -fcompare-debug testcase.C
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-amd64/bin/x86_64-pc-linux-gnu-g++
COLLECT_LTO_WRAPPER=/repo/gcc-trunk/binary-trunk-r10-7738-20200415114440-g49795733fdc-checking-yes-rtl-df-extra-amd64/bin/../libexec/gcc/x86_64-pc-linux-gnu/10.0.1/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-r10-7738-20200415114440-g49795733fdc-checking-yes-rtl-df-extra-amd64
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 10.0.1 20200415 (experimental) (GCC)

[Bug debug/94618] [8/9/10 Regression] '-fcompare-debug' failure (length) with -O2 -fnon-call-exceptions since r8-565-g7581ce9a1ad6df9c

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94618

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|                            |7.4.0
                 CC|                            |marxin at gcc dot gnu.org,
                   |                            |rguenth at gcc dot gnu.org
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2020-04-16
     Ever confirmed|0                           |1
            Summary|[10 Regression]             |[8/9/10 Regression]
                   |'-fcompare-debug' failure   |'-fcompare-debug' failure
                   |(length) with -O2           |(length) with -O2
                   |-fnon-call-exceptions       |-fnon-call-exceptions since
                   |                            |r8-565-g7581ce9a1ad6df9c
      Known to fail|                            |8.3.0, 9.3.0
   Target Milestone|---                         |8.5

--- Comment #1 from Martin Liška <marxin at gcc dot gnu.org> ---
With -fno-ipa-sra it started with r8-565-g7581ce9a1ad6df9c.

[Bug debug/94618] [8/9/10 Regression] '-fcompare-debug' failure (length) with -O2 -fnon-call-exceptions since r8-565-g7581ce9a1ad6df9c

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94618

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

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

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
I'll have a look.

[Bug rtl-optimization/94618] [8/9/10 Regression] '-fcompare-debug' failure (length) with -O2 -fnon-call-exceptions since r8-565-g7581ce9a1ad6df9c

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94618

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |vmakarov at gcc dot gnu.org
           Keywords|                            |ra
          Component|debug                       |rtl-optimization

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
diff --git a/gcc/tree-cfg.c b/gcc/tree-cfg.c
index e99fb9ff5d1..e508d736de8 100644
--- a/gcc/tree-cfg.c
+++ b/gcc/tree-cfg.c
@@ -9019,7 +9019,7 @@ split_critical_edges (bool for_edge_insertion_p /* =
false */)
            {
              gimple_stmt_iterator gsi;

-             gsi = gsi_last_bb (e->src);
+             gsi = gsi_last_nondebug_bb (e->src);
              if (!gsi_end_p (gsi)
                  && stmt_ends_bb_p (gsi_stmt (gsi))
                  && (gimple_code (gsi_stmt (gsi)) != GIMPLE_RETURN

Doesn't fix it, disabling tail merging doesn't either.

The difference is

--- t.gkd       2020-04-16 16:15:15.906645135 +0200
+++ t.gk.gkd    2020-04-16 16:15:16.082647662 +0200
@@ -29,7 +29,7 @@
             (pc))) "t.C":17:5# {*jcc}
      (expr_list:REG_DEAD (reg:CCZ 17 flags)
         (int_list:REG_BR_PROB 536870916 (nil)))
- -> 13)
+ -> 14)
 (note # 0 0 [bb 3] NOTE_INSN_BASIC_BLOCK)
 (note # 0 0 NOTE_INSN_DELETED)
 (insn/f:TI # 0 0 3 (set (mem:DI (pre_dec:DI (reg/f:DI 7 sp)) [  S8 A8])
@@ -74,13 +74,13 @@
                 (const_int 8 [0x8])) [ MEM[(struct S *)this_2(D) + 8B].ae+0 S4
A32])) "t.C":8:12# {*movsi_internal}
      (expr_list:REG_EH_REGION (const_int -5 [0xfffffffffffffffb])
         (nil)))
+(note # 0 0 # NOTE_INSN_EH_REGION_BEG)
 (insn # 0 0 3 (set (reg:CCZ 17 flags)
         (compare:CCZ (mem:SI (plus:DI (reg/f:DI 5 di [orig:93 this ] [93])
                     (const_int 12 [0xc])) [ MEM[(struct S *)this_2(D) +
8B].af+0 S4 A32])
             (reg:SI 6 bp [orig:87 _10 ] [87]))) "t.C":18:28# {*cmpsi_1}
      (expr_list:REG_DEAD (reg/f:DI 5 di [orig:93 this ] [93])
-        (expr_list:REG_EH_REGION (const_int -6 [0xfffffffffffffffa])
-            (nil))))
+        (nil)))
 (jump_insn # 0 0 3 (set (pc)
         (if_then_else (eq (reg:CCZ 17 flags)
                 (const_int 0 [0]))
@@ -98,7 +98,6 @@
 (insn # 0 0 4 (set (reg:DI 5 di)
         (reg/f:DI 41 r13 [orig:82 _1 ] [82])) "t.C":19:4# {*movdi_internal}
      (nil))
-(note # 0 0 # NOTE_INSN_EH_REGION_BEG)
 (call_insn:TI # 0 0 4 (call (mem:QI (symbol_ref:DI ("_ZN1S1iEi") [flags 0x41] 
<function_decl # i>) [ i S1 A8])
         (const_int 0 [0])) "t.C":19:4# {*call}
      (expr_list:REG_DEAD (reg:DI 5 di)
@@ -246,7 +245,7 @@
  -> simple_return)
 (barrier # 0 0)
 (note # 0 0 NOTE_INSN_DELETED)
-(code_label # 0 0 9 13 (nil) [1 uses])
+(code_label # 0 0 9 14 (nil) [1 uses])
 (note # 0 0 [bb 9] NOTE_INSN_BASIC_BLOCK)
 (insn:TI # 0 0 9 (unspec_volatile [
             (const_int 0 [0])

but on GIMPLE I cannot see any difference in EH info.

Starting with LRA I see the disconnect with REG_EH_REGION notes on insn 17 /
41:

(insn 17 16 18 3 (set (reg:CCZ 17 flags)
        (compare:CCZ (mem:SI (plus:DI (reg/f:DI 3 bx [orig:93 this ] [93])
                    (const_int 12 [0xc])) [1 MEM[(struct S *)this_2(D) +
8B].af+0 S4 A32])
            (reg:SI 6 bp [orig:87 _10 ] [87]))) "t.C":18:28 11 {*cmpsi_1}
     (expr_list:REG_EH_REGION (const_int -6 [0xfffffffffffffffa])
        (nil)))

vs.

(insn 41 40 42 3 (set (reg:CCZ 17 flags)
        (compare:CCZ (mem:SI (plus:DI (reg/f:DI 3 bx [orig:93 this ] [93])
                    (const_int 12 [0xc])) [1 MEM[(struct S *)this_2(D) +
8B].af+0 S4 A32])
            (reg:SI 6 bp [orig:87 _10 ] [87]))) "t.C":18:28 11 {*cmpsi_1}
     (nil))

[Bug rtl-optimization/94618] [8/9/10 Regression] '-fcompare-debug' failure (length) with -O2 -fnon-call-exceptions since r8-565-g7581ce9a1ad6df9c

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94618

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
I think the difference is much earlier, in cse_local dump there is (with
additional --param=min-nondebug-insn-uid=10000):
 deferring deletion of insn with uid = 10060.
-deferring deletion of insn with uid = 10059.
-Deleted 2 trivially dead insns
+Deleted 1 trivially dead insns
where the RA then removes the trivially dead insn when cse_local didn't.

[Bug rtl-optimization/94618] [8/9/10 Regression] '-fcompare-debug' failure (length) with -O2 -fnon-call-exceptions since r8-565-g7581ce9a1ad6df9c

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94618

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

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

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 48293
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=48293&action=edit
gcc10-pr94618.patch

Untested fix.

[Bug rtl-optimization/94618] [8/9/10 Regression] '-fcompare-debug' failure (length) with -O2 -fnon-call-exceptions since r8-565-g7581ce9a1ad6df9c

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94618

--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #5)
> Created attachment 48293 [details]
> gcc10-pr94618.patch
> 
> Untested fix.

Looks logically correct - but are there no helpers for this on the RTL side?
Like LAST_NONDEBUG_INSN (BB) or so?  Or skip_debug_insns_until_bb_end?
Possibly this is the only such case of course ...

[Bug rtl-optimization/94618] [8/9/10 Regression] '-fcompare-debug' failure (length) with -O2 -fnon-call-exceptions since r8-565-g7581ce9a1ad6df9c

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94618

--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Perhaps if we checked DEBUG_INSN_P on BB_END, we could then use
prev_nondebug_insn, so like:
  if (INSN_P (insn) && BLOCK_FOR_INSN (insn))
    {
      basic_block bb = BLOCK_FOR_INSN (insn);
      if (BB_END (bb) == insn
          || (DEBUG_INSN_P (BB_END (bb))
              && prev_nondebug_insn (BB_END (bb)) == insn))
        purge = true;
    }
?

[Bug rtl-optimization/94618] [8/9/10 Regression] '-fcompare-debug' failure (length) with -O2 -fnon-call-exceptions since r8-565-g7581ce9a1ad6df9c

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94618

--- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Though, a slight advantage of the patch as is is that it will do any insn walk
only if two conditions are met, BB_END is a DEBUG_INSN and insn is followed by
a DEBUG_INSN.  My thoughs were that there could be a large bb with hundreds of
DEBUG_INSNs at the end and if we e.g. started deleting insn from the start,
even if they aren't really followed by any DEBUG_INSNs, we'd still walk all of
them each time.

[Bug rtl-optimization/94618] [8/9/10 Regression] '-fcompare-debug' failure (length) with -O2 -fnon-call-exceptions since r8-565-g7581ce9a1ad6df9c

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94618

--- Comment #9 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:c41884a09206be0e21cad7eea71b9754daa969d4

commit r10-7769-gc41884a09206be0e21cad7eea71b9754daa969d4
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Fri Apr 17 10:33:27 2020 +0200

    Fix -fcompare-debug issue in delete_insn_and_edges [PR94618]

    delete_insn_and_edges calls purge_dead_edges whenever deleting the last
insn
    in a bb, whatever it is.  If it called it only for mandatory last insns
    in the basic block (that may not be followed by DEBUG_INSNs, dunno if that
    is control_flow_insn_p or something more complex), that wouldn't be a
    problem, but as it calls it on any last insn and can actually do something
    in the bb, if such an insn is followed by one more more DEBUG_INSNs and
    nothing else in the same bb, we don't call purge_dead_edges with -g and do
    call it with -g0.

    On the testcase, there are two reg-to-reg moves with REG_EH_REGION notes
    (previously memory accesses but simplified and yet not optimized), and the
    second is followed by DEBUG_INSNs; the second move is delete_insn_and_edges
    and after removing it, for -g0 purge_dead_edges removes the REG_EH_REGION
    from the now last insn in the bb (the first reg-to-reg move), while
    for -g it isn't called and things diverge from that quickly on.

    Fixed by calling purdge_dead_edges even if we remove the last real insn
    followed only by DEBUG_INSNs in the same bb.

    2020-04-17  Jakub Jelinek  <jakub@redhat.com>

            PR rtl-optimization/94618
            * cfgrtl.c (delete_insn_and_edges): Set purge not just when
            insn is the BB_END of its block, but also when it is only followed
            by DEBUG_INSNs in its block.

            * g++.dg/opt/pr94618.C: New test.

[Bug rtl-optimization/94618] [8/9 Regression] '-fcompare-debug' failure (length) with -O2 -fnon-call-exceptions since r8-565-g7581ce9a1ad6df9c

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94618

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[8/9/10 Regression]         |[8/9 Regression]
                   |'-fcompare-debug' failure   |'-fcompare-debug' failure
                   |(length) with -O2           |(length) with -O2
                   |-fnon-call-exceptions since |-fnon-call-exceptions since
                   |r8-565-g7581ce9a1ad6df9c    |r8-565-g7581ce9a1ad6df9c

--- Comment #10 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Fixed on the trunk (so far).

[Bug rtl-optimization/94618] [8/9 Regression] '-fcompare-debug' failure (length) with -O2 -fnon-call-exceptions since r8-565-g7581ce9a1ad6df9c

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94618

--- Comment #11 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-9 branch has been updated by Jakub Jelinek
<jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:dea597314f4503228e23e887ddbb773cbf197093

commit r9-8881-gdea597314f4503228e23e887ddbb773cbf197093
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Fri Apr 17 10:33:27 2020 +0200

    Fix -fcompare-debug issue in delete_insn_and_edges [PR94618]

    delete_insn_and_edges calls purge_dead_edges whenever deleting the last
insn
    in a bb, whatever it is.  If it called it only for mandatory last insns
    in the basic block (that may not be followed by DEBUG_INSNs, dunno if that
    is control_flow_insn_p or something more complex), that wouldn't be a
    problem, but as it calls it on any last insn and can actually do something
    in the bb, if such an insn is followed by one more more DEBUG_INSNs and
    nothing else in the same bb, we don't call purge_dead_edges with -g and do
    call it with -g0.

    On the testcase, there are two reg-to-reg moves with REG_EH_REGION notes
    (previously memory accesses but simplified and yet not optimized), and the
    second is followed by DEBUG_INSNs; the second move is delete_insn_and_edges
    and after removing it, for -g0 purge_dead_edges removes the REG_EH_REGION
    from the now last insn in the bb (the first reg-to-reg move), while
    for -g it isn't called and things diverge from that quickly on.

    Fixed by calling purdge_dead_edges even if we remove the last real insn
    followed only by DEBUG_INSNs in the same bb.

    2020-04-17  Jakub Jelinek  <jakub@redhat.com>

            PR rtl-optimization/94618
            * cfgrtl.c (delete_insn_and_edges): Set purge not just when
            insn is the BB_END of its block, but also when it is only followed
            by DEBUG_INSNs in its block.

            * g++.dg/opt/pr94618.C: New test.

    (cherry picked from commit c41884a09206be0e21cad7eea71b9754daa969d4)

[Bug rtl-optimization/94618] [8/9 Regression] '-fcompare-debug' failure (length) with -O2 -fnon-call-exceptions since r8-565-g7581ce9a1ad6df9c

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94618

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

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

--- Comment #12 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Fixed for 8.5 in r8-10488-g00191dfc2914b2e66a3fbe50aa79ef6a5fc2be46 and by the
above commit for 9.4+ too.

[Bug rtl-optimization/94618] [8/9 Regression] '-fcompare-debug' failure (length) with -O2 -fnon-call-exceptions since r8-565-g7581ce9a1ad6df9c

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94618
Bug 94618 depends on bug 105559, which changed state.

Bug 105559 Summary: [10 Regression] -g and -O3 cause timeout since r12-156-g8d4c374c4419a875
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105559

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