[Bug debug/100523] New: [11/12 Regression] armv8.1-m.main -fcompare-debug failure with -O -fmodulo-sched -mtune=cortex-a53

[Bug debug/100523] New: [11/12 Regression] armv8.1-m.main -fcompare-debug failure with -O -fmodulo-sched -mtune=cortex-a53

[acoplan at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100523

            Bug ID: 100523
           Summary: [11/12 Regression] armv8.1-m.main -fcompare-debug
                    failure with -O -fmodulo-sched -mtune=cortex-a53
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: debug
          Assignee: unassigned at gcc dot gnu.org
          Reporter: acoplan at gcc dot gnu.org
  Target Milestone: ---

The following fails:

$ cat test.c
int main_j;
int main() {
  long crc;
  for (; main_j; main_j--)
    if (crc)
      crc = crc >> 1 ^ 20;
}
$ ./arm-eabi-gcc -c test.c -fcompare-debug -O -fmodulo-sched
-march=armv8.1-m.main -mfloat-abi=soft -mtune=cortex-a53
arm-eabi-gcc: error: test.c: '-fcompare-debug' failure

Obviously the choice of scheduling isn't sensible for this -march, but it
reveals a bug in any case.

[Bug debug/100523] [11/12 Regression] armv8.1-m.main -fcompare-debug failure with -O -fmodulo-sched -mtune=cortex-a53

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100523

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |11.2

[Bug debug/100523] [11/12 Regression] armv8.1-m.main -fcompare-debug failure with -O -fmodulo-sched -mtune=cortex-a53

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100523

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|11.2                        |11.3

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 11.2 is being released, retargeting bugs to GCC 11.3

[Bug debug/100523] [11/12 Regression] armv8.1-m.main -fcompare-debug failure with -O -fmodulo-sched -mtune=cortex-a53

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100523

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|11.3                        |11.4

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 11.3 is being released, retargeting bugs to GCC 11.4.

[Bug debug/100523] [11/12/13 Regression] armv8.1-m.main -fcompare-debug failure with -O -fmodulo-sched -mtune=cortex-a53

[ramana at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100523

Ramana Radhakrishnan <ramana at gcc dot gnu.org> changed:

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

--- Comment #3 from Ramana Radhakrishnan <ramana at gcc dot gnu.org> ---
It does fall over but isn't this is a bit of an undefined testcase given that
crc is an uninitialised local variable used before initialisation ? 

What am I missing ? 

Ramana

[Bug debug/100523] [11/12/13 Regression] armv8.1-m.main -fcompare-debug failure with -O -fmodulo-sched -mtune=cortex-a53

[acoplan at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100523

--- Comment #4 from Alex Coplan <acoplan at gcc dot gnu.org> ---
Looks like it also falls over with this testcase:

int main_j;
long x;
int main() {
  long crc = x;
  for (; main_j; main_j--)
    if (crc)
      crc = crc >> 1 ^ 20;
}

which fixes the uninitialized use

[Bug debug/100523] [11/12/13/14 Regression] armv8.1-m.main -fcompare-debug failure with -O -fmodulo-sched -mtune=cortex-a53

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100523

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|11.4                        |11.5

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 11.4 is being released, retargeting bugs to GCC 11.5.

[Bug debug/100523] [11/12/13/14 Regression] armv8.1-m.main -fcompare-debug failure with -O -fmodulo-sched -mtune=cortex-a53

[law at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100523

Jeffrey A. Law <law at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |law at gcc dot gnu.org
           Priority|P3                          |P4

[Bug debug/100523] [11/12/13/14 Regression] armv8.1-m.main -fcompare-debug failure with -O -fmodulo-sched -mtune=cortex-a53

[rearnsha at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100523

Richard Earnshaw <rearnsha at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2024-03-06
     Ever confirmed|0                           |1

--- Comment #6 from Richard Earnshaw <rearnsha at gcc dot gnu.org> ---
Confirmed on trunk (14.0.1 20240215)

+++ cd.gk.c.gkd 2024-03-06 10:21:59.679317666 +0000
@@ -71,6 +71,7 @@
      (nil))
 (code_label # 0 0 5 4 (nil) [1 uses])
 (note # 0 0 [bb 5] NOTE_INSN_BASIC_BLOCK)
+(note # 0 0 NOTE_INSN_DELETED)
 (insn # 0 0 5 (set (reg:CC 100 cc)
         (compare:CC (reg/v:SI 3 r3 [orig:116 crc ] [116])
             (const_int 0 [0]))) "cd.c":7:11# {*arm_cmpsi_insn}
@@ -99,7 +100,6 @@
                     (const_int -1 [0xffffffffffffffff])))
         ]) "cd.c":5:10 discrim 1# {thumb2_addsi3_compare0}
      (nil))
-(note # 0 0 NOTE_INSN_DELETED)
 (insn # 0 0 5 (set (reg:SI 2 r2 [orig:114 _1 ] [114])
         (ashiftrt:SI (reg/v:SI 3 r3 [orig:116 crc ] [116])
             (const_int 1 [0x1]))) "cd.c":7:11# {*arm_shiftsi3}


So it's probably harmless in this case, but still shouldn't happen.