[Bug debug/104180] New: [10/11/12 Regression] '-fcompare-debug' failure (length) w/ -O1

[Bug debug/104180] New: [10/11/12 Regression] '-fcompare-debug' failure (length) w/ -O1

[asolokha at gmx dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104180

            Bug ID: 104180
           Summary: [10/11/12 Regression] '-fcompare-debug' failure
                    (length) w/ -O1
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Keywords: compare-debug-failure
          Severity: normal
          Priority: P3
         Component: debug
          Assignee: unassigned at gcc dot gnu.org
          Reporter: asolokha at gmx dot com
  Target Milestone: ---

g++ 12.0.0 20220109 snapshot (g:90045c5df5b3c8853e7740fb72a11aead1c489bb) fails
-fcompare-debug check when compiling the following testcase, reduced from
gcc/testsuite/gcc.dg/torture/pr89223.c, w/ -O1:

int a[5];

void
c ()
{
  unsigned int b;

  for (b = 3; ; b--)
    a[b] = ({ a[b + 1]; });
}

% g++-12.0.0 -O1 -fcompare-debug -c lluhupiv.c
g++-12.0.0: error: lluhupiv.c: '-fcompare-debug' failure (length)

--- lluhupiv.c.gkd      2022-01-22 15:27:16.168639041 +0700
+++ lluhupiv.gk.c.gkd   2022-01-22 15:27:16.239634334 +0700
@@ -33,7 +33,7 @@
      (nil))
 (insn # 0 0 3 (set (mem:SI (plus:DI (mult:DI (reg:DI 2 cx [orig:87 b ] [87])
                     (const_int 4 [0x4]))
-                (reg/f:DI 5 di [86])) [ a[b_3]+0 S4 A32])
+                (reg/f:DI 5 di [86])) [ MEM <int[5]> [(int *)&a][b_3]+0 S4
A32])
         (reg:SI 4 si [orig:82 _2 ] [82])) "lluhupiv.c":9:10# {*movsi_internal}
      (expr_list:REG_DEAD (reg:SI 4 si [orig:82 _2 ] [82])
         (expr_list:REG_DEAD (reg:DI 2 cx [orig:87 b ] [87])

[Bug debug/104180] [10/11/12 Regression] '-fcompare-debug' failure (length) w/ -O1

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104180

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2022-01-22
   Target Milestone|---                         |10.4
             Status|UNCONFIRMED                 |NEW
                 CC|                            |jakub at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Started with r11-963-g80d6f89e78fc3b772701988cc73aa8e8006283be
which has been backported to 10.x in r10-8355-g7d919c33fbd29

[Bug c++/104180] [10/11/12 Regression] '-fcompare-debug' failure (length) w/ -O1

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104180

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|middle-end                  |c++

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
[apinski@xeond2 src]$ diff -up t.cc.*original t.gk.cc.*original |less
--- t.cc.005t.original  2022-01-22 03:44:26.901343652 -0800
+++ t.gk.cc.005t.original       2022-01-22 03:44:27.005343663 -0800
@@ -6,13 +6,19 @@
 {
   unsigned int b;

+  # DEBUG BEGIN STMT;
     unsigned int b;
+  # DEBUG BEGIN STMT;
   <<cleanup_point <<< Unknown tree: expr_stmt
     (void) (b = 3) >>>>>;
   <D.2374>:;
+  # DEBUG BEGIN STMT;
   <<cleanup_point <<< Unknown tree: expr_stmt
-    (void) (a[b] = a[b + 1]) >>>>>;
+    (void) (a[b] = # DEBUG BEGIN STMT;
+    a[b + 1];) >>>>>;
+  # DEBUG BEGIN STMT;
   <<cleanup_point (void) b-- >>;
+  # DEBUG BEGIN STMT;
   goto <D.2374>;
 }



And then we gimplify:
+  # DEBUG BEGIN_STMT
+  # DEBUG BEGIN_STMT
   b = 3;
   <D.2374>:
-  _1 = b + 1;
-  _2 = a[_1];
-  a[b] = _2;
+  # DEBUG BEGIN_STMT
+  _1 = &a[b];
+  # DEBUG BEGIN_STMT
+  _2 = b + 1;
+  _3 = a[_2];
+  *_1 = _3;
+  # DEBUG BEGIN_STMT
   b = b + 4294967295;
+  # DEBUG BEGIN_STMT
   goto <D.2374>;

[Bug c++/104180] [10/11/12 Regression] '-fcompare-debug' failure (length) w/ -O1

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104180

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=100733,
                   |                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=103788

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Similar in nature to PR 100733 and PR 103788.

[Bug c++/104180] [10/11/12 Regression] '-fcompare-debug' failure (length) w/ -O1

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104180

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

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

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
If it is because of -gstatement-frontiers, I've ran out of ideas how to fix
them.
So unless Alexandre is willing to look at it, I'd suggest to at least turn
-gstatement-frontiers off by default.

[Bug c++/104180] [10/11/12 Regression] '-fcompare-debug' failure (length) w/ -O1

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104180

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2
                 CC|                            |rguenth at gcc dot gnu.org

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
I think it's reasonable to turn them off (OTOH we then probably lose all test
coverage).  IIRC gdb doensn't handle any of the advanced debug stuff GCC emits
(like views)?

[Bug c++/104180] [10/11/12 Regression] '-fcompare-debug' failure (length) w/ -O1

[asolokha at gmx dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104180

--- Comment #6 from Arseny Solokha <asolokha at gmx dot com> ---
Meanwhile, I've finally added -gno-statement-frontiers to my testing scripts.

[Bug c++/104180] [10/11/12 Regression] '-fcompare-debug' failure (length) w/ -O1

[aoliva at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104180

--- Comment #7 from Alexandre Oliva <aoliva at gcc dot gnu.org> ---
I've recommended before that, without any plan to implement consumers for this
debug information, keeping it in place is mostly wasteful.  AFAICT other debug
stmts issued by front-ends could hit the same issue, but those are only
theoretical IIRC.  On the one hand, disabling the feature would hide the known
problem that codegen is sensitive to such debug stmts, but on the other, we can
cross that bridge if we get to it again.

[Bug c++/104180] [10/11/12/13 Regression] '-fcompare-debug' failure (length) w/ -O1

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104180

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|10.4                        |10.5

--- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 10.4 is being released, retargeting bugs to GCC 10.5.

[Bug c++/104180] [11/12/13/14 Regression] '-fcompare-debug' failure (length) w/ -O1

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104180

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|10.5                        |11.5

--- Comment #9 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 10 branch is being closed.