[Bug tree-optimization/63446] dangling reference results in confusing diagnostic from -Wuninitialized

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* [Bug tree-optimization/63446] dangling reference results in confusing diagnostic from -Wuninitialized
       [not found] <bug-63446-4@http.gcc.gnu.org/bugzilla/>
@ 2014-10-03  0:16 ` manu at gcc dot gnu.org
  2014-10-03  7:10 ` glisse at gcc dot gnu.org
                   ` (6 subsequent siblings)
  7 siblings, 0 replies; 8+ messages in thread
From: manu at gcc dot gnu.org @ 2014-10-03  0:16 UTC (permalink / raw)
  To: gcc-bugs

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63446

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2014-10-03
                 CC|                            |manu at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #1 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
> In an ideal world gcc would warn about the last line of make_foo() instead
> of func(), and it would mention a dangling reference instead of an
> uninitialized use.

Hum, yes, but I'm not even sure if GCC realizes that there is a dangling
reference. However, it should since the code looks like:

foo make_foo() ()
Eh tree:
   1 cleanup
     2 cleanup
{
  intD.9 & SR.1D.2273;
  intD.9 xD.2244;
  struct fooD.2226 D.2254;
  struct fooD.2226 D.2260;

;;   basic block 2, loop depth 0, count 0, freq 10000, maybe hot
;;    prev block 0, next block 1, flags: (NEW, REACHABLE)
;;    pred:       ENTRY (FALLTHRU,EXECUTABLE)
;;   starting at line 10
  [test.c : 10:11] # .MEM_2 = VDEF <.MEM_1(D)>
  xD.2244 = 42;
  [test.c : 11:15] # .MEM_4 = VDEF <.MEM_2>
  [test.c : 11] MEM[(struct fooD.2226 *)&D.2260] = &xD.2244;
  # .MEM_6 = VDEF <.MEM_4>
  xD.2244 ={v} {CLOBBER};
  [test.c : 11:15] # VUSE <.MEM_6>
  return D.2260;
;;    succ:       EXIT (EXECUTABLE)

}

which is just before x = 42 is removed. But for the same reason that it is
removed, perhaps also the dangling reference could be detected.
>From gcc-bugs-return-463152-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Fri Oct 03 01:32:49 2014
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From: "bobby.prani at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/63444] Compilation consumes 2.5G memory
Date: Fri, 03 Oct 2014 01:32:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idc444

--- Comment #1 from Pranith Kumar <bobby.prani at gmail dot com> ---
Just FYI, clang compiles the same file using 1G memory.


^ permalink raw reply	[flat|nested] 8+ messages in thread

* [Bug tree-optimization/63446] dangling reference results in confusing diagnostic from -Wuninitialized
       [not found] <bug-63446-4@http.gcc.gnu.org/bugzilla/>
  2014-10-03  0:16 ` [Bug tree-optimization/63446] dangling reference results in confusing diagnostic from -Wuninitialized manu at gcc dot gnu.org
@ 2014-10-03  7:10 ` glisse at gcc dot gnu.org
  2014-10-03  7:18 ` glisse at gcc dot gnu.org
                   ` (5 subsequent siblings)
  7 siblings, 0 replies; 8+ messages in thread
From: glisse at gcc dot gnu.org @ 2014-10-03  7:10 UTC (permalink / raw)
  To: gcc-bugs

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63446

--- Comment #2 from Marc Glisse <glisse at gcc dot gnu.org> ---
make_foo:

  MEM[(struct foo *)&D.2281] = &x;
  x ={v} {CLOBBER};
  return D.2281;

That doesn't seem so easy to warn about. We could walk from return to find some
of the latest non-clobbered dominating writes to that variable, then if it is
an ADDR_EXPR look for dominating clobbers, but that would be very specialized,
slight variations on this code would not warn (and all those walks may start to
get costly if we do them naively). It is easier to warn in the caller when it
tries to dereference the dangling pointer.

^ permalink raw reply	[flat|nested] 8+ messages in thread

* [Bug tree-optimization/63446] dangling reference results in confusing diagnostic from -Wuninitialized
       [not found] <bug-63446-4@http.gcc.gnu.org/bugzilla/>
  2014-10-03  0:16 ` [Bug tree-optimization/63446] dangling reference results in confusing diagnostic from -Wuninitialized manu at gcc dot gnu.org
  2014-10-03  7:10 ` glisse at gcc dot gnu.org
@ 2014-10-03  7:18 ` glisse at gcc dot gnu.org
  2014-10-03 11:37 ` manu at gcc dot gnu.org
                   ` (4 subsequent siblings)
  7 siblings, 0 replies; 8+ messages in thread
From: glisse at gcc dot gnu.org @ 2014-10-03  7:18 UTC (permalink / raw)
  To: gcc-bugs

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63446

--- Comment #3 from Marc Glisse <glisse at gcc dot gnu.org> ---
(In reply to Marc Glisse from comment #2)
> make_foo:
> 
>   MEM[(struct foo *)&D.2281] = &x;
>   x ={v} {CLOBBER};
>   return D.2281;
> 
> That doesn't seem so easy to warn about. We could walk from return to find
> some of the latest non-clobbered dominating writes to that variable, then if
> it is an ADDR_EXPR look for dominating clobbers, but that would be very
> specialized,

Hmm, actually, we can probably ignore the clobber, returning an object that
contains a pointer to a local variable is the issue. That's already a bit more
doable.

Not sure what the best pass would be to add this though. Returning (directly) a
pointer to a temporary is handled in isolate-paths IIRC, but that might not be
as good a fit for this.


^ permalink raw reply	[flat|nested] 8+ messages in thread

* [Bug tree-optimization/63446] dangling reference results in confusing diagnostic from -Wuninitialized
       [not found] <bug-63446-4@http.gcc.gnu.org/bugzilla/>
                   ` (2 preceding siblings ...)
  2014-10-03  7:18 ` glisse at gcc dot gnu.org
@ 2014-10-03 11:37 ` manu at gcc dot gnu.org
  2014-10-03 12:13 ` glisse at gcc dot gnu.org
                   ` (3 subsequent siblings)
  7 siblings, 0 replies; 8+ messages in thread
From: manu at gcc dot gnu.org @ 2014-10-03 11:37 UTC (permalink / raw)
  To: gcc-bugs

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63446

--- Comment #4 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
(In reply to Marc Glisse from comment #2)
> make_foo:
> 
>   MEM[(struct foo *)&D.2281] = &x;
>   x ={v} {CLOBBER};
>   return D.2281;
> 
> That doesn't seem so easy to warn about. We could walk from return to find
> some of the latest non-clobbered dominating writes to that variable, then if
> it is an ADDR_EXPR look for dominating clobbers, but that would be very
> specialized, slight variations on this code would not warn (and all those
> walks may start to get costly if we do them naively). It is easier to warn
> in the caller when it tries to dereference the dangling pointer.

At some moment (in dcce1), gcc decides that x = 4 is not needed. For the same
reason, it could realize that MEM[(struct foo *)&D.2281] = &x must produce a
dangling reference, no?
>From gcc-bugs-return-463176-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Fri Oct 03 12:06:32 2014
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Subject: [Bug c/63448] ICE when compiling atlas 3.10.2
Date: Fri, 03 Oct 2014 12:06:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idc448

--- Comment #5 from Svante Signell <svante.signell at gmail dot com> ---
FYI: atlas builds fine with gcc-4.8.3-11 (and gfortran-4.9-15)


^ permalink raw reply	[flat|nested] 8+ messages in thread

* [Bug tree-optimization/63446] dangling reference results in confusing diagnostic from -Wuninitialized
       [not found] <bug-63446-4@http.gcc.gnu.org/bugzilla/>
                   ` (3 preceding siblings ...)
  2014-10-03 11:37 ` manu at gcc dot gnu.org
@ 2014-10-03 12:13 ` glisse at gcc dot gnu.org
  2014-10-03 13:51 ` glisse at gcc dot gnu.org
                   ` (2 subsequent siblings)
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From: glisse at gcc dot gnu.org @ 2014-10-03 12:13 UTC (permalink / raw)
  To: gcc-bugs

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63446

--- Comment #5 from Marc Glisse <glisse at gcc dot gnu.org> ---
(In reply to Manuel López-Ibáñez from comment #4)
> At some moment (in dcce1), gcc decides that x = 4 is not needed. For the
> same reason, it could realize that MEM[(struct foo *)&D.2281] = &x must
> produce a dangling reference, no?

A clobber implies that the content is lost, so it is useless to store something
there right before the clobber (I assume that's why the store is removed, I
didn't check), but I don't believe it implies that the memory location is
reclaimed (does it?), so it would be fine to store a pointer in some struct,
kill what that pointer points to, re-create something there, use that, etc.
Without the return statement, it is normal to remove x=4 (because of the
clobber), but I don't see anything to warn about, while we could warn with a
return statement and no clobber, so the 2 things seem quite different.

Of course I may be looking at this the wrong way.
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Subject: [Bug c/63445] request: make -Wstrict-overflow avoid a class of false positives
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63445

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2014-10-03
                 CC|                            |manu at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #1 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
I'm going to confirm this even if it is not clear it is possible to fix this.

Also, I think it is a bug that the loop condition has the location of the "for"
keyword and not of the "<" expression when lowering to gimple. That is,

 [test.c : 8:7] if (iD.1622 < nD.1621) goto <D.1623>; else goto <D.1625>; 

should be

 [test.c : 8:33] if (iD.1622 < nD.1621) goto <D.1623>; else goto <D.1625>; 

It gets even more confusing if the "i < n" is in the next line:

test.c:8:7: warning: assuming signed overflow does not occur when simplifying
conditional [-Wstrict-overflow]
       for (unsigned int i = 0;
       ^
>From gcc-bugs-return-463179-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Fri Oct 03 12:39:27 2014
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Subject: [Bug tree-optimization/63446] dangling reference results in confusing diagnostic from -Wuninitialized
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63446

--- Comment #6 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
(In reply to Marc Glisse from comment #5)
> A clobber implies that the content is lost, so it is useless to store
> something there right before the clobber (I assume that's why the store is
> removed, I didn't check), but I don't believe it implies that the memory
> location is reclaimed (does it?), so it would be fine to store a pointer in
> some struct, kill what that pointer points to, re-create something there,
> use that, etc. Without the return statement, it is normal to remove x=4
> (because of the clobber), but I don't see anything to warn about, while we
> could warn with a return statement and no clobber, so the 2 things seem
> quite different.

OK, that makes sense. Thanks for the explanation. 

What about checking that the return value, if it is a VUSE, is not assigned to
a local? That is, this would be valid, assuming y is not local,

  MEM[(struct foo *)&D.2281] = &x;
  MEM[(struct foo *)&D.2281] = &y;
  return D.2281;

 but this would not be:

  MEM[(struct foo *)&D.2281] = &x;
  return D.2281;

It doesn't matter, whether x is clobbered or has a value and also it doesn't
matter what is executed between the assignment and the return as long as it
doesn't change the value of MEM[(struct foo *)&D.2281]. It could be a matter of
following the chain of VUSE->VDEF, which I think we already do for
Wuninitialized.
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Subject: [Bug libstdc++/63449] documentation of vector space overhead management
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idc449

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |documentation
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2014-10-03
           Assignee|unassigned at gcc dot gnu.org      |redi at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
("documentation" is a keyword, the component should be "libstdc++" so that the
relevant maintainers deal with it.)

I don't know/remember anything about that new implementation, but it never
happened so I think we can just remove the section.

The list::size() documentation above needs updating though.


^ permalink raw reply	[flat|nested] 8+ messages in thread

* [Bug tree-optimization/63446] dangling reference results in confusing diagnostic from -Wuninitialized
       [not found] <bug-63446-4@http.gcc.gnu.org/bugzilla/>
                   ` (4 preceding siblings ...)
  2014-10-03 12:13 ` glisse at gcc dot gnu.org
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  2014-10-03 14:57 ` manu at gcc dot gnu.org
  2021-04-16 17:17 ` msebor at gcc dot gnu.org
  7 siblings, 0 replies; 8+ messages in thread
From: glisse at gcc dot gnu.org @ 2014-10-03 13:51 UTC (permalink / raw)
  To: gcc-bugs

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63446

--- Comment #7 from Marc Glisse <glisse at gcc dot gnu.org> ---
(In reply to Manuel López-Ibáñez from comment #6)
> What about [...]

That's roughly what I describe in comment #2, amended by comment #3.

> It could be a matter of following the chain of VUSE->VDEF,
> which I think we already do for Wuninitialized.

IIRC we don't, and the file contains a comment saying that it would be
expensive. Actually, properly limiting the maximal depth of the walk (as is
done in several other passes) would make it cheap enough and we should probably
do it.

Note that if make_foo was static or inline, it wouldn't exist anymore in the
uninit pass.
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From: "ubizjak at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/57003] [4.8/4.9/5.0 Regression] gcc breaks -O2 optimization with Wine(64) - links/info/bisect of commits included
Date: Fri, 03 Oct 2014 14:23:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57003

Uroš Bizjak <ubizjak at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|FIXED                       |---
   Target Milestone|4.8.1                       |5.0
            Summary|[4.8/4.9 Regression]        |[4.8/4.9/5.0 Regression]
                   |gcc-4.8.0 breaks -O2        |gcc breaks -O2 optimization
                   |optimization with Wine(64)  |with Wine(64) -
                   |- links/info/bisect of      |links/info/bisect of
                   |commits included            |commits included

--- Comment #23 from Uroš Bizjak <ubizjak at gmail dot com> ---
My r215428 change regressed this PR again. The difference is:

--- pr57003.s   2014-10-03 15:08:24.000000000 +0200
+++ pr57003_.s  2014-10-03 15:08:19.000000000 +0200
@@ -78,7 +78,7 @@
        leaq    -20(%rbx), %rdx
        movq    %rax, %rdi
        call    memcpy
-       movq    %rdi, c(%rip)
+       movq    %rax, c(%rip)
 .L8:
        movaps  (%rsp), %xmm6
        movaps  16(%rsp), %xmm7
@@ -321,5 +321,5 @@
        .byte   0xb
        .align 8
 .LEFDE7:
-       .ident  "GCC: (GNU) 5.0.0 20141002 (experimental) [trunk revision
215797]"
+       .ident  "GCC: (GNU) 4.9.2 20141001 (prerelease) [gcc-4_9-branch
revision 215749]"
        .section        .note.GNU-stack,"",@progbits

So, gcc-5.0 does not detect that %rdi is clobbered in ELF ABI.

The runtime failure happens only on CentOS5 (and not in Fedora20), which
supports findings in Comment #17.

The difference is, that previously we emit memcpy call as:

#(call_insn:TI 24 23 27 3 (set (reg:DI 0 ax)
#        (call (mem:QI (symbol_ref:DI ("memcpy") [flags 0x41] <function_decl
0x7fce6f586438 memcpy>) [0 memcpy S1 A8])
#            (const_int 0 [0]))) pr57003.c:32 661 {*call_value}
#     (expr_list:REG_DEAD (reg:DI 5 di)
#        (expr_list:REG_DEAD (reg:DI 4 si)
#            (expr_list:REG_DEAD (reg:DI 1 dx)
#                (expr_list:REG_UNUSED (reg:DI 0 ax)
#                    (expr_list:REG_RETURNED (reg/v/f:DI 2 cx [orig:87 e ]
[87])
#                        (expr_list:REG_CALL_DECL (symbol_ref:DI ("memcpy")
[flags 0x41] <function_decl 0x7fce6f586438 memcpy>)
#                            (expr_list:REG_EH_REGION (const_int 0 [0])
#                                (nil))))))))
#    (expr_list (clobber (reg:TI 52 xmm15))
#        (expr_list (clobber (reg:TI 51 xmm14))
#            (expr_list (clobber (reg:TI 50 xmm13))
#                (expr_list (clobber (reg:TI 49 xmm12))
#                    (expr_list (clobber (reg:TI 48 xmm11))
#                        (expr_list (clobber (reg:TI 47 xmm10))
#                            (expr_list (clobber (reg:TI 46 xmm9))
#                                (expr_list (clobber (reg:TI 45 xmm8))
#                                    (expr_list (clobber (reg:TI 28 xmm7))
#                                        (expr_list (clobber (reg:TI 27 xmm6))
#                                            (expr_list (clobber (reg:DI 5 di))
#                                                (expr_list (clobber (reg:DI 4
si))
#                                                    (expr_list:DI (set (reg:DI
0 ax)
#                                                            (reg:DI 5 di))
#                                                        (expr_list:DI (use
(reg:DI 5 di))
#                                                            (expr_list:DI (use
(reg:DI 4 si))
#                                                                (expr_list:DI
(use (reg:DI 1 dx))
#                                                                   
(nil))))))))))))))))))

which is alternate, but equivalent form of what was generated previously:

#(call_insn:TI 24 23 27 3 (parallel [
#            (set (reg:DI 0 ax)
#                (call (mem:QI (symbol_ref:DI ("memcpy") [flags 0x41]
<function_decl 0x7fd91824a800 memcpy>) [0 memcpy S1 A8])
#                    (const_int 0 [0])))
#            (unspec [
#                    (const_int 0 [0])
#                ] UNSPEC_MS_TO_SYSV_CALL)
#            (clobber (reg:DI 4 si))
#            (clobber (reg:DI 5 di))
#            (clobber (reg:TI 27 xmm6))
#            (clobber (reg:TI 28 xmm7))
#            (clobber (reg:TI 45 xmm8))
#            (clobber (reg:TI 46 xmm9))
#            (clobber (reg:TI 47 xmm10))
#            (clobber (reg:TI 48 xmm11))
#            (clobber (reg:TI 49 xmm12))
#            (clobber (reg:TI 50 xmm13))
#            (clobber (reg:TI 51 xmm14))
#            (clobber (reg:TI 52 xmm15))
#        ]) pr57003.c:32 652 {*call_value_rex64_ms_sysv}
#     (expr_list:REG_DEAD (reg:DI 5 di)
#        (expr_list:REG_DEAD (reg:DI 4 si)
#            (expr_list:REG_DEAD (reg:DI 1 dx)
#                (expr_list:REG_RETURNED (reg/v/f:DI 2 cx [orig:87 e ] [87])
#                    (expr_list:REG_EH_REGION (const_int 0 [0])
#                        (nil))))))
#    (expr_list:DI (set (reg:DI 0 ax)
#            (reg:DI 5 di))
#        (expr_list:DI (use (reg:DI 5 di))
#            (expr_list:DI (use (reg:DI 4 si))
#                (expr_list:DI (use (reg:DI 1 dx))
#                    (nil))))))

It looks that Jakub's patch, proposed in Comment #21 doesn't cover alternative
form, so it doesn't record clobbers in the alternative form properly.

Reopened as 5.0 regression.
>From gcc-bugs-return-463191-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Fri Oct 03 14:23:13 2014
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From: "chefmax at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug testsuite/58867] asan and ubsan tests not run for installed testing
Date: Fri, 03 Oct 2014 14:23:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idX867

Maxim Ostapenko <chefmax at gcc dot gnu.org> changed:

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

--- Comment #5 from Maxim Ostapenko <chefmax at gcc dot gnu.org> ---
This is fixed by r215793, but I forgot to mention it in commit message. So, ok
to resolve as fixed?


^ permalink raw reply	[flat|nested] 8+ messages in thread

* [Bug tree-optimization/63446] dangling reference results in confusing diagnostic from -Wuninitialized
       [not found] <bug-63446-4@http.gcc.gnu.org/bugzilla/>
                   ` (5 preceding siblings ...)
  2014-10-03 13:51 ` glisse at gcc dot gnu.org
@ 2014-10-03 14:57 ` manu at gcc dot gnu.org
  2021-04-16 17:17 ` msebor at gcc dot gnu.org
  7 siblings, 0 replies; 8+ messages in thread
From: manu at gcc dot gnu.org @ 2014-10-03 14:57 UTC (permalink / raw)
  To: gcc-bugs

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63446

--- Comment #8 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
(In reply to Marc Glisse from comment #7)
> IIRC we don't, and the file contains a comment saying that it would be
> expensive. Actually, properly limiting the maximal depth of the walk (as is
> done in several other passes) would make it cheap enough and we should
> probably do it.

I hope so. You may even fix PR19430 in the process, which is one of the oldest
PRs we have!
>From gcc-bugs-return-463202-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Fri Oct 03 15:02:12 2014
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Subject: [Bug libstdc++/63449] documentation of vector space overhead management
Date: Fri, 03 Oct 2014 15:02:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idc449

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Author: redi
Date: Fri Oct  3 15:01:36 2014
New Revision: 215855

URL: https://gcc.gnu.org/viewcvs?rev!5855&root=gcc&view=rev
Log:
    PR libstdc++/63449
    * doc/xml/manual/containers.xml: Remove outdated section. Update
    std::list notes.
    * doc/html/*: Regenerate.

Modified:
    branches/gcc-4_8-branch/libstdc++-v3/ChangeLog
    branches/gcc-4_8-branch/libstdc++-v3/doc/html/index.html
    branches/gcc-4_8-branch/libstdc++-v3/doc/html/manual/containers.html
    branches/gcc-4_8-branch/libstdc++-v3/doc/html/manual/index.html
    branches/gcc-4_8-branch/libstdc++-v3/doc/html/manual/std_contents.html
    branches/gcc-4_8-branch/libstdc++-v3/doc/xml/manual/containers.xml


^ permalink raw reply	[flat|nested] 8+ messages in thread

* [Bug tree-optimization/63446] dangling reference results in confusing diagnostic from -Wuninitialized
       [not found] <bug-63446-4@http.gcc.gnu.org/bugzilla/>
                   ` (6 preceding siblings ...)
  2014-10-03 14:57 ` manu at gcc dot gnu.org
@ 2021-04-16 17:17 ` msebor at gcc dot gnu.org
  7 siblings, 0 replies; 8+ messages in thread
From: msebor at gcc dot gnu.org @ 2021-04-16 17:17 UTC (permalink / raw)
  To: gcc-bugs

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63446

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|2014-10-03 00:00:00         |2021-4-16
      Known to fail|                            |10.2.0, 11.0, 4.6.4, 4.9.4,
                   |                            |5.5.0, 6.4.0, 7.2.0, 8.3.0,
                   |                            |9.1.0
                 CC|                            |msebor at gcc dot gnu.org
           Severity|normal                      |enhancement
             Blocks|                            |49974

--- Comment #9 from Martin Sebor <msebor at gcc dot gnu.org> ---
GCC 11 improves the message by including a note that mentions the uninitialized
variable.  In this case it doesn't completely solve the problem because the
variable it points to is initialized but it should help.

pr63446.C: In function ‘int func()’:
pr63446.C:15:14: warning: ‘x’ is used uninitialized [-Wuninitialized]
   15 |     return f.ref;
      |              ^~~
pr63446.C:8:9: note: ‘x’ was declared here
    8 |     int x = 42;
      |         ^

But the underlying bug here is returning a reference to a local variable, so
the warning to improve is -Wreturn-local-addr.  That will diagnose the return
statement in make_foo().  Bug 49974 tracks that enhancement.  With that, the
additional -Wuninitialized issued in func() would just help clarify the
consequences of the bug but not otherwise be essential.


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=49974
[Bug 49974] missing -Wreturn-local-addr for indirectly returning reference to
local/temporary

^ permalink raw reply	[flat|nested] 8+ messages in thread

end of thread, other threads:[~2021-04-16 17:17 UTC | newest]

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2014-10-03  0:16 ` [Bug tree-optimization/63446] dangling reference results in confusing diagnostic from -Wuninitialized manu at gcc dot gnu.org
2014-10-03  7:10 ` glisse at gcc dot gnu.org
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