[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])