[Bug ada/64548] New: Lost visibility of package System after raise

[Bug ada/64548] New: Lost visibility of package System after raise

[simon at pushface dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64548

            Bug ID: 64548
           Summary: Lost visibility of package System after raise
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: ada
          Assignee: unassigned at gcc dot gnu.org
          Reporter: simon at pushface dot org

Created attachment 34410
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=34410&action=edit
Reproducer (to be gnatchopped)

In the attached, a raise statement with a string expression causes the compiler
to lose visibility of package System.

In this cut-down reproducer, removing the string expression makes the problem
go away; however this workround doesn’t work in the full code.

Same problem in GCC 4.8, 4.9 & GNAT GPL 2013, 2014.

I found the problem while compiling for arm-eabi but this also happens for
x86_64-apple-darwin13 and with the Linux GNAT GPL 2013.

     4.    function Create_Task
     5.      (Code        : Task_Code;
     6.       Name        : String;
     7.       Stack_Depth : Natural;
     8.       Parameters  : System.Address;
     9.       Priority    : System.Any_Priority)
    10.      return Task_Handle is
    11.    begin
    12.       raise Program_Error with "couldn't create task";
    13.
    14.       return Null_Task_Handle;
    15.    end Create_Task;
    16.
    17.    function Get_Application_Parameter return System.Address is
                    1                                3
        >>> not type conformant with declaration at buggy_freertos.ads:19
        >>> return type does not match
        >>> "System" is not visible (more references follow)
        >>> non-visible declaration at system.ads:55

Using -gnatdg shows
      $ada__exceptions__raise_exception (ada__exceptions__null_id,
        "couldn't create task");
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Subject: [Bug c++/56126] -fno-exceptions should activate -fcheck-new or issue diagnostic for all new operators without throw()
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idV126

--- Comment #14 from Michael Bruck <bruck.michael at googlemail dot com> ---
(In reply to Olaf van der Spek from comment #12)
> > Allocation failure is a
> > simple error and should not kill your program.
>
> It's far from simple to handle properly and to do better then abort.

In systems that use different types of allocators for different purposes it can
be a fairly common case.

> >> BTW, what's your use case? Do you really want to check NULL on every
> >> call to new?
> >
> > With -fno-exceptions you have to check all functions for errors, including
> > allocation.
>
> What's your use case?

Memory constrained systems

[Bug ada/64548] Lost visibility of package System after raise

[simon at pushface dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64548

--- Comment #1 from simon at pushface dot org ---
As you may have gathered, I’m building an RTS.

It turns out that the fault is triggered - regardless of -gnatg - if there is
a-except.ads in the same directory which says “private with System;”.

I have resolved this for myself by changing Ada.Exceptions.Exception_Id to “new
Integer”.
>From gcc-bugs-return-472704-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Sat Jan 10 20:51:08 2015
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From: "simon at pushface dot org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug ada/64556] New: Aspect Preelaborate is ignored on library-level subprogram
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64556

            Bug ID: 64556
           Summary: Aspect Preelaborate is ignored on library-level
                    subprogram
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: ada
          Assignee: unassigned at gcc dot gnu.org
          Reporter: simon at pushface dot org

Attempting to mark a library-level supbprogram as preelaborable via an aspect
doesn’t work; you still need to use the pragma.

This:

with System;
procedure Last_Chance_Handler
  (Message : System.Address; Line : Integer)
with
  Preelaborate,
  Export,
  Convention => C,
  External_Name => "__gnat_last_chance_handler";

results in

arm-eabi-gcc -c -gnatpgn -gnatqQ -nostdinc -ffunction-sections -fdata-sections
-g -O0 -g -O1 -fno-inline -fno-toplevel-reorder a-except.adb
a-except.adb:21:06: warning: cannot depend on "Last_Chance_Handler" (wrong
categorization)
a-except.adb:21:06: warning: preelaborated unit cannot depend on
non-preelaborated unit

Also in gcc version 5.0.0 20141228 (experimental) (GCC)
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From: "wmi at google dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/64557] New: get_addr in true_dependence_1 cannot handle VALUE inside an expr
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idd557

            Bug ID: 64557
           Summary: get_addr in true_dependence_1 cannot handle VALUE
                    inside an expr
           Product: gcc
           Version: 4.9.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: wmi at google dot com

We saw a bug in dse2 after porting the patch
https://gcc.gnu.org/ml/gcc-patches/2014-10/msg01209.html from gcc-4_9 to
google-4_9 branch. From the analysis below, I think the problem exists but is
hidden in trunk and gcc-4_9 too. I cannot extract a small testcase to show it
independently without turning on some optimization in google-4_9, so I just
described it here:

We have such IR in a case:

The IR before dse2:
(insn/f 67 4 68 2 (set (mem:DI (pre_dec:DI (reg/f:DI 7 sp)) [0  S8 A8])
        (reg/f:DI 6 bp)) contentads/adx/mixer/auction/candidate.cc:14 -1
     (nil))
(insn/f 68 67 69 2 (set (reg/f:DI 6 bp)
        (reg/f:DI 7 sp)) contentads/adx/mixer/auction/candidate.cc:14 -1
     (nil))
(insn/f 70 69 71 2 (parallel [
            (set (reg/f:DI 7 sp)
                (plus:DI (reg/f:DI 7 sp)
                    (const_int -24 [0xffffffffffffffe8])))
            (clobber (reg:CC 17 flags))
            (clobber (mem:BLK (scratch) [0  A8]))
        ]) contentads/adx/mixer/auction/candidate.cc:14 -1
     (nil))
(note 71 70 2 2 NOTE_INSN_PROLOGUE_END)
....
(insn 7 3 9 2 (set (mem/c:SI (reg/f:DI 7 sp) [0 MEM[(void *)&D.3507754]+0 S4
A128])
        (const_int 0 [0])) ./ads/base/money.h:67 90 {*movsi_internal}
     (nil))
(insn 9 7 10 2 (set (mem/c:HI (reg/f:DI 7 sp) [0 MEM[(void *)&D.3507754]+0 S2
A128])
        (const_int 21333 [0x5355])) ./ads/base/money.h:68 92 {*movhi_internal}
     (nil))
(insn 10 9 11 2 (set (mem/c:QI (plus:DI (reg/f:DI 7 sp)
                (const_int 2 [0x2])) [0 MEM[(void *)&D.3507754]+2 S1 A16])
        (const_int 68 [0x44])) ./ads/base/money.h:68 93 {*movqi_internal}
     (nil))
(insn 11 10 12 2 (set (reg:SI 0 ax [orig:87 D.3507754 ] [87])
        (mem/c:SI (reg/f:DI 7 sp) [0 D.3507754+0 S4 A128]))
./ads/base/money.h:302 90 {*movsi_internal}
     (expr_list:REG_EQUIV (mem/c:SI (plus:DI (reg/f:DI 20 frame)
                (const_int -16 [0xfffffffffffffff0])) [0 D.3507754+0 S4 A128])
        (nil)))
...
(insn 15 13 17 2 (set (mem/c:SI (reg/f:DI 7 sp) [0 MEM[(void *)&D.3507756]+0 S4
A128])
        (const_int 0 [0])) ./ads/base/money.h:67 90 {*movsi_internal}
     (nil))

The IR after dse2:
The store in insn 10 is deleted. The other part is the same as above.

(mem/c:QI (plus:DI (reg/f:DI 7 sp) (const_int 2 [0x2])) in insn10 is regarded
to have no alias with (mem/c:SI (reg/f:DI 7 sp) in insn11, which is wrong. This
is because with the applied patch, get_addr is used to extract original
addresses for x_addr and mem_addr before they are used to find_base_term and
used in base_alias_check. See the description of x_addr and mem_addr below:

x is (mem/c:SI (reg/f:DI 7 sp)
x_addr before calling get_addr is:
(value:DI 4:12939 @0x84355f8/0x84354a0)
x_addr after calling get_addr is:
(plus:DI (value:DI 3:8637 @0x84355e8/0x8435478)
    (const_int -24 [0xffffffffffffffe8]))
x_addr_base is: (address:DI -4)

mem is (mem/c:QI (plus:DI (reg/f:DI 7 sp) (const_int 2 [0x2]))
mem_addr before calling get_addr is:
(plus:DI (value:DI 4:12939 @0x84355f8/0x84354a0)
    (const_int 2 [0x2]))
mem_addr after calling get_addr is:  // Notice: get_addr cannot handle plus
expr, so it returns the origin expr.
(plus:DI (value:DI 4:12939 @0x84355f8/0x84354a0)
    (const_int 2 [0x2]))
mem_addr_base is: (address:DI -1)

// value:DI 4:12939 @0x84355f8/0x84354a0 corresponds to reg/f:DI 7 sp
// value:DI 3:8637 @0x84355e8/0x8435478 corresponds to reg/f:DI 6 bp
// address:DI -1 corresponds to reg/f:DI 7 sp
// address:DI -4 corresponds to reg/f:DI 6 bp

x_addr_base and mem_addr_base are different, and unique_base_value_p will
return true for (address:DI -1) and (address:DI -4), so base_alias_check will
return 0, which is wrong.

I think the root cause of the problem is get_addr can only handle VALUE but
cannot handle VALUE inside an expr, like:(plus:DI (value:DI 4:12939
@0x84355f8/0x84354a0) (const_int 2 [0x2])), so find_base_term cannot know
x_addr and mem_addr actually have the same base.

[Bug ada/64548] Lost visibility of package System after raise

[simon at pushface dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64548

--- Comment #2 from simon at pushface dot org ---
See PR64866 for a similar problem/workround.

[Bug ada/64548] Lost visibility of package System after raise

[demoonlit at panathenaia dot halfmoon.jp]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64548

--- Comment #5 from yuta tomino <demoonlit at panathenaia dot halfmoon.jp> ---
Hello, Simon.
I'm glad to look at this report.

I have a similar experience like this.
The trigger of mine was not "private with" but a nested package in the spec of
Ada.Exceptions.

I should think it's useless information, but I would write, just in case.