[Bug tree-optimization/63748] New: may be used uninitialized warning on variable definition with initializer

[Bug tree-optimization/63748] New: may be used uninitialized warning on variable definition with initializer

[amodra at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63748

            Bug ID: 63748
           Summary: may be used uninitialized warning on variable
                    definition with initializer
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: amodra at gmail dot com

Created attachment 33892
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=33892&action=edit
preprocessed source

Found when compiling gdb's eval.c using gcc-4.9.1 or current trunk,
x86_64-linux or powerpc64-linux.

/src/binutils-gdb/gdb/eval.c: In function ‘evaluate_subexp_standard’:
/src/binutils-gdb/gdb/eval.c:745:16: error: ‘ret’ may be used uninitialized in
this function [-Werror=maybe-uninitialized]
  struct value *ret = NULL;
                ^

More bogus warnings follow with -O -Wall on the attached preprocessed source.
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From: "mkuvyrkov at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug debug/61033] [4.8/4.9 Regression] Infinite loop in variable tracking
Date: Wed, 05 Nov 2014 12:55:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?ida033

--- Comment #10 from Maxim Kuvyrkov <mkuvyrkov at gcc dot gnu.org> ---
Michael,

What is the status of this bug?

Thanks.

[Bug tree-optimization/63748] [4.9/5 Regression] may be used uninitialized warning on variable definition with initializer

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63748

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2014-11-05
                 CC|                            |mpolacek at gcc dot gnu.org
   Target Milestone|---                         |4.9.3
            Summary|may be used uninitialized   |[4.9/5 Regression] may be
                   |warning on variable         |used uninitialized warning
                   |definition with initializer |on variable definition with
                   |                            |initializer
     Ever confirmed|0                           |1

--- Comment #1 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Confirmed.

[Bug tree-optimization/63748] [4.9/5 Regression] may be used uninitialized warning on variable definition with initializer

[uweigand at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63748

Ulrich Weigand <uweigand at gcc dot gnu.org> changed:

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

--- Comment #2 from Ulrich Weigand <uweigand at gcc dot gnu.org> ---
Much simplified test case:

typedef struct __jmp_buf_tag jmp_buf;
extern int setjmp (jmp_buf *);
jmp_buf *alloc_jmp_buf ();
int foo (void *);

int
test (int op, int noside)
{
  void *argvec = 0;

  if (op)
    {
      jmp_buf *buf = alloc_jmp_buf ();
      setjmp (buf);

      if (noside)
        goto nosideret;

    do_call_it:

      if (noside)
        goto nosideret;

      return foo (argvec);
    }

  argvec = __builtin_alloca (1);
  goto do_call_it;

nosideret:
  return 1;
}

results in:

xxx.i: In function ‘test’:
xxx.i:14:16: error: ‘buf’ may be used uninitialized in this function
[-Werror=maybe-uninitialized]
       jmp_buf *buf = alloc_jmp_buf ();
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From: "howarth at bromo dot med.uc.edu" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/63773] [meta-bug] Restoring darwin bootstrap for gcc 5.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63773

--- Comment #4 from howarth at bromo dot med.uc.edu ---
(In reply to Francois-Xavier Coudert from comment #3)
> I'd like to help, but it's such a mess. There is not one PR per distinct
> issue, but various things reported in long threads. 
> 
> Regarding the first two patches (libcc1 and ipa-chkp.c), they are
> straightforward and should be approved fast. Don't hesitate to ping them
> every few days.
> 
> The "nonlocal goto and setjmp" patch has been committed.
> 
> But… the remaining patch
> (https://gcc.gnu.org/bugzilla/attachment.cgi?id=33843) does not appear
> enough to restore bootstrap. I still get:
> 
> ld: illegal text reloc in 'std::strstream::strstream()' to 'construction
> vtable for std::basic_ostream<char, std::char_traits<char>
> >-in-std::strstream' for architecture x86_64
> 
> is there another patch required?

Did you apply the PA ICF aliasing restriction patch from
https://gcc.gnu.org/bugzilla/attachment.cgi?id=33843? Without it, the new
ipa-icf pass will erroneously attempt alias creation on targets which don't
support (it like MACH-O on darwin). The cryptic "ld: illegal text reloc" error
is emitted from the darwin linker because the use of "-undefined
dynamic_lookup" masks the fact that undefined symbols result from the
inappropriate alias creation.

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63622#c12
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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/63748] [4.9/5 Regression] may be used uninitialized warning on variable definition with initializer
Date: Fri, 07 Nov 2014 22:03:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idc748

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I think this is hard warning to avoid in the compiler as we don't know if foo
calls longjmp or not.  Note we don't know if alloc_jmp_buf does a push
somewhere else.

[Bug tree-optimization/63748] [4.9/5 Regression] may be used uninitialized warning on variable definition with initializer

[uweigand at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63748

--- Comment #4 from Ulrich Weigand <uweigand at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #3)
> I think this is hard warning to avoid in the compiler as we don't know if
> foo calls longjmp or not.  Note we don't know if alloc_jmp_buf does a push
> somewhere else.

Huh?  No matter what, "buf" is in fact never used uninitialized in this
function, and that should be trivial to see; the only use of "buf" occurs in
line 17 immediately after the definition of "buf" in line 16, whether any
longjmp is ever called or not.

Also, if any of the gotos in this function is removed, the warning disappears. 
The problem seems to be related to some call-graph optimizations (note that the
if (noside) check is partially redundant).

[Bug tree-optimization/63748] [4.9/5 Regression] wrong may be used uninitialized warning (abnormal edges)

[uweigand at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63748

--- Comment #6 from Ulrich Weigand <uweigand at gcc dot gnu.org> ---
I guess I can see why there might be an abnormal edge starting at bb 3, or at
least, that the compiler might not be easily able to deduce that it isn't
necessary.

However, I do not understand why any of the abnormal edges *target* bb5
*before* the setjmp call.  Shouldn't an abnormal edge due to a longjmp end up
*after* the setjmp?  After all, the setjmp itself (including the preparation of
its arguments) is *not* executed twice; the effect of the longjmp is simply to
make the setjmp *return* twice.

[Bug tree-optimization/63748] [4.9/5 Regression] wrong may be used uninitialized warning (abnormal edges)

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63748

--- Comment #7 from ppalka at gcc dot gnu.org ---
Author: ppalka
Date: Mon Nov 10 20:43:40 2014
New Revision: 217317

URL: https://gcc.gnu.org/viewcvs?rev=217317&root=gcc&view=rev
Log:
2014-11-10  Patrick Palka  <ppalka@gcc.gnu.org>

gcc/
    PR middle-end/63748
    * tree-ssa-propagate.c (may_propagate_copy): Allow propagating
    SSA copies whose source and destination names both occur in
    abnormal PHIs.

gcc/testsuite/
    PR middle-end/63748
    * gcc.dg/pr63748.c: New testcase.


Added:
    trunk/gcc/testsuite/gcc.dg/pr63748.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree-ssa-propagate.c

[Bug tree-optimization/63748] [4.9/5 Regression] wrong may be used uninitialized warning (abnormal edges)

[amodra at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63748

--- Comment #8 from Alan Modra <amodra at gmail dot com> ---
Thanks!  Fix confirmed with gdb sources prior to the workaround Uli committed. 
Is the fix appropriate for gcc-4.9?  If not, I'll be happy to adjust the target
milestone and close the bug.

[Bug tree-optimization/63748] [4.9 Regression] wrong may be used uninitialized warning (abnormal edges)

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63748

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic
      Known to work|                            |5.0
            Summary|[4.9/5 Regression] wrong    |[4.9 Regression] wrong may
                   |may be used uninitialized   |be used uninitialized
                   |warning (abnormal edges)    |warning (abnormal edges)

--- Comment #9 from Richard Biener <rguenth at gcc dot gnu.org> ---
I think the fix is appropriate to backport if its prerequesite (making
out-of-SSA coalescing ignore default defs) are backported.

Fixed on trunk.

[Bug tree-optimization/63748] [4.9 Regression] wrong may be used uninitialized warning (abnormal edges)

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63748

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2

[Bug tree-optimization/63748] [4.9 Regression] wrong may be used uninitialized warning (abnormal edges)

[manu at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63748

Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Blocks|                            |24639
         Depends on|24639                       |

--- Comment #10 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
Fix blocks/depends list
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Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Blocks|                            |24639
         Depends on|24639                       |

--- Comment #3 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
Fix blocks/depends list.
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Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |manu at gcc dot gnu.org
             Blocks|                            |24639
         Depends on|24639                       |

--- Comment #2 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
Fix blocks/depends list.
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Subject: [Bug tree-optimization/65178] incorrect -Wmaybe-uninitialized when using nested loops
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65178

Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-02-23
                 CC|                            |manu at gcc dot gnu.org
             Blocks|                            |24639
     Ever confirmed|0                           |1

--- Comment #1 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
A minimized testcase:

void *bar(int);
char *
foo (void)
{ 
  char *c = "bla";
  char *buf;
  for (int a = 1;; a = 0)
    { 
      for (char *s = c; *s; ++s)
        { 
        }
      if (!a) break;
      buf = (char *) bar (1);
    }
  return buf;
}

It fails in GCC 5.0 with -O1, -O2 and -O3. I think we have several reports
about this: GCC simply does not understand that the loop body is executed at
least once, thus there should be no (default) entry edge for the PHI node of
buf.

I think it is a missed optimization also: If buf were initialized, the initial
value could be dropped.
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Subject: [Bug fortran/61831] [4.9/ 5 Regression] runtime error: pointer being freed was not allocated
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61831

--- Comment #42 from Mikael Morin <mikael at gcc dot gnu.org> ---
(In reply to Mikael Morin from comment #41)
> My work patch is:

updated work patch below.
The testcase passes with it, at the price of leaking memory

Index: trans-expr.c
===================================================================
--- trans-expr.c    (révision 220717)
+++ trans-expr.c    (copie de travail)
@@ -4949,7 +4949,8 @@ gfc_conv_procedure_call (gfc_se * se, gfc_symbol *
       if (e && (e->ts.type == BT_DERIVED || e->ts.type == BT_CLASS)
         && e->ts.u.derived->attr.alloc_comp
         && !(e->symtree && e->symtree->n.sym->attr.pointer)
-        && (e->expr_type != EXPR_VARIABLE && !e->rank))
+        && (e->expr_type != EXPR_VARIABLE
+        && e->expr_type != EXPR_STRUCTURE && !e->rank))
         {
       int parm_rank;
       tmp = build_fold_indirect_ref_loc (input_location,
@@ -7131,7 +7132,8 @@ gfc_conv_expr_reference (gfc_se * se, gfc_expr * e
   if (expr->ts.type == BT_DERIVED && expr->rank
       && !gfc_is_finalizable (expr->ts.u.derived, NULL)
       && expr->ts.u.derived->attr.alloc_comp
-      && expr->expr_type != EXPR_VARIABLE)
+      && expr->expr_type != EXPR_VARIABLE
+      && expr->expr_type != EXPR_ARRAY)
     {
       tree tmp;
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Subject: [Bug bootstrap/65150] [5 Regression] r220875 causes bootstrap failure on x86_64 darwin
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https://gcc.gnu.org/bugzilla/show_bug.cgi?ide150

--- Comment #9 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Iain Sandoe from comment #7)
> here we fall through to the case were we make a thunk - IFF we were not able
> to rmove the alias.  However, potentially, we already moved all the callers
> from the alias to the original.
>
> (a) is that safe?

Why not?

> (b) we might as well avoid the work by testing whether the alias will be
> removable before we set redirect_callers?

Redirecting the callers is beneficial even when we create trunk.
For the redirected callers, they will jump directly to the right function,
while
without redirection you call a thunk, which in the better case just jumps to
the right function (ie. sibcall), in the worse case calls it and then returns.
So you save a few instructions on each redirected call.
When alias is created instead of redirection (in that case we don't redirect
callers right now), the only advantage of redirection would be tail recursion.

[Bug tree-optimization/63748] [4.9 Regression] wrong may be used uninitialized warning (abnormal edges)

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63748

--- Comment #11 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 4.9.3 has been released.

[Bug tree-optimization/63748] [4.9 Regression] wrong may be used uninitialized warning (abnormal edges)

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63748

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.9.3                       |4.9.4