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From: "asolokha at gmx dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug debug/104263] New: [10/11/12 Regression] '-fcompare-debug'
 failure (length) w/ -O2 -fnon-call-exceptions -fno-inline-small-functions
Date: Fri, 28 Jan 2022 02:51:04 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D104263

            Bug ID: 104263
           Summary: [10/11/12 Regression] '-fcompare-debug' failure
                    (length) w/ -O2 -fnon-call-exceptions
                    -fno-inline-small-functions
           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: ---

gcc 12.0.1 20220123 snapshot (g:2da90ad39bf8fa9ee287e040d1f4411cb7a2e7ed) f=
ails
-fcompare-debug check when compiling the following testcase w/ -O2
-fnon-call-exceptions -fno-inline-small-functions:

int n;

int
bar (void)
{
  int a;

  n =3D 0;
  a =3D 0;

  return n;
}

__attribute__ ((pure, returns_twice)) int
foo (void)
{
  n =3D bar () + 1;
  foo ();

  return 0;
}

% gcc-12.0.1 -O2 -fcompare-debug -fnon-call-exceptions
-fno-inline-small-functions -gno-statement-frontiers -c ovslsrlb.c
x86_64-pc-linux-gnu-gcc-12.0.1: error: ovslsrlb.c: '-fcompare-debug' failure
(length)

For x86_64 the difference looks like this, though the failure is not
target-specific:

--- ovslsrlb.c.gkd      2022-01-28 09:42:43.969435346 +0700
+++ ovslsrlb.gk.c.gkd   2022-01-28 09:42:43.987435394 +0700
@@ -40,8 +40,8 @@
 (note # 0 0 [bb 2] NOTE_INSN_BASIC_BLOCK)
 (note # 0 0 NOTE_INSN_PROLOGUE_END)
 (note # 0 0 NOTE_INSN_FUNCTION_BEG)
-(insn:TI # 0 0 2 (set (mem/c:SI (symbol_ref:DI ("n") [flags 0x2]  <var_dec=
l #
n>) [ MEM[(int *)&n]+0 S4 A32])
-        (const_int 1 [0x1])) "ovslsrlb.c":8:5# {*movsi_internal}
+(insn:TI # 0 0 2 (set (mem/c:SI (symbol_ref:DI ("n") [flags 0x2]  <var_dec=
l #
n>) [ n+0 S4 A32])
+        (const_int 1 [0x1])) "ovslsrlb.c":17:5# {*movsi_internal}
      (nil))
 (insn # 0 0 2 (parallel [
             (set (reg:DI 0 ax)=