[PATCH] Do not erase warning data in gimple_set_location

[PATCH] Do not erase warning data in gimple_set_location

[Eric Botcazou]

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Hi,

gimple_set_location is mostly invoked on newly built GIMPLE statements, so 
their location is UNKNOWN_LOCATION and setting it will clobber the warning 
data of the passed location, if any.

Tested on x86-64/Linux, OK for mainline and 12 branch?


2022-06-10  Eric Botcazou  <ebotcazou@adacore.com>

	* gimple.h (gimple_set_location): Do not copy warning data from
	the previous location when it is UNKNOWN_LOCATION.


2022-06-10  Eric Botcazou  <ebotcazou@adacore.com>

testsuite/
	* c-c++-common/nonnull-1.c: Remove XFAIL for C++.

-- 
Eric Botcazou

[-- Attachment #2: p.diff --]
[-- Type: text/x-patch, Size: 986 bytes --]

diff --git a/gcc/gimple.h b/gcc/gimple.h
index 6b1e89ad74e..870629cd562 100644
--- a/gcc/gimple.h
+++ b/gcc/gimple.h
@@ -1913,7 +1913,8 @@ static inline void
 gimple_set_location (gimple *g, location_t location)
 {
   /* Copy the no-warning data to the statement location.  */
-  copy_warning (location, g->location);
+  if (g->location != UNKNOWN_LOCATION)
+    copy_warning (location, g->location);
   g->location = location;
 }
 
diff --git a/gcc/testsuite/c-c++-common/nonnull-1.c b/gcc/testsuite/c-c++-common/nonnull-1.c
index ea987365302..7be4e3479dd 100644
--- a/gcc/testsuite/c-c++-common/nonnull-1.c
+++ b/gcc/testsuite/c-c++-common/nonnull-1.c
@@ -30,5 +30,5 @@ func (char *cp1, char *cp2, char *cp3, char *cp4)
 __attribute__((nonnull (1))) int
 func2 (char *cp)
 {
-  return (cp != NULL) ? 1 : 0; /* { dg-warning "'nonnull' argument" "cp compared to NULL" { xfail c++ } } */
+  return (cp != NULL) ? 1 : 0; /* { dg-warning "'nonnull' argument" "cp compared to NULL" } */
 }

Re: [PATCH] Do not erase warning data in gimple_set_location

[Jeff Law]

On 6/10/2022 4:57 AM, Eric Botcazou via Gcc-patches wrote:
> Hi,
>
> gimple_set_location is mostly invoked on newly built GIMPLE statements, so
> their location is UNKNOWN_LOCATION and setting it will clobber the warning
> data of the passed location, if any.
>
> Tested on x86-64/Linux, OK for mainline and 12 branch?
>
>
> 2022-06-10  Eric Botcazou  <ebotcazou@adacore.com>
>
> 	* gimple.h (gimple_set_location): Do not copy warning data from
> 	the previous location when it is UNKNOWN_LOCATION.
>
>
> 2022-06-10  Eric Botcazou  <ebotcazou@adacore.com>
>
> testsuite/
> 	* c-c++-common/nonnull-1.c: Remove XFAIL for C++.
OK for trunk and gcc-12.
jeff

Re: [PATCH] Do not erase warning data in gimple_set_location

[Richard Biener]

On Fri, Jun 10, 2022 at 12:58 PM Eric Botcazou via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> Hi,
>
> gimple_set_location is mostly invoked on newly built GIMPLE statements, so
> their location is UNKNOWN_LOCATION and setting it will clobber the warning
> data of the passed location, if any.

Hmm, I think instead of special-casing UNKNOWN_LOCATION
what gimple_set_location should probably do is either not copy
warnings at all or union them.  Btw, gimple_set_location also
removes a previously set BLOCK (but gimple_set_block preserves
the location locus and diagnostic override).

So I'd be tempted to axe the copy_warning () completely here.  Martin,
there were
probably cases that warranted it - do you remember anything specific here?

Thanks,
Richard.

> Tested on x86-64/Linux, OK for mainline and 12 branch?
>
>
> 2022-06-10  Eric Botcazou  <ebotcazou@adacore.com>
>
>         * gimple.h (gimple_set_location): Do not copy warning data from
>         the previous location when it is UNKNOWN_LOCATION.
>
>
> 2022-06-10  Eric Botcazou  <ebotcazou@adacore.com>
>
> testsuite/
>         * c-c++-common/nonnull-1.c: Remove XFAIL for C++.
>
> --
> Eric Botcazou

Re: [PATCH] Do not erase warning data in gimple_set_location

[Martin Sebor]

On 6/13/22 05:15, Richard Biener wrote:
> On Fri, Jun 10, 2022 at 12:58 PM Eric Botcazou via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
>>
>> Hi,
>>
>> gimple_set_location is mostly invoked on newly built GIMPLE statements, so
>> their location is UNKNOWN_LOCATION and setting it will clobber the warning
>> data of the passed location, if any.
> 
> Hmm, I think instead of special-casing UNKNOWN_LOCATION
> what gimple_set_location should probably do is either not copy
> warnings at all or union them.  Btw, gimple_set_location also
> removes a previously set BLOCK (but gimple_set_block preserves
> the location locus and diagnostic override).
> 
> So I'd be tempted to axe the copy_warning () completely here.  Martin,
> there were
> probably cases that warranted it - do you remember anything specific here?

Nothing specific, just that the assumption behind the warning group
design was that a location must exist in order to suppress a warning
(a location is one of the first things that's set early on by the FE
and it makes little sense to issue a warning without one).

There was and in all likelihood still is code sets TREE_NO_WARNING
or gimple_no_warning on new trees/statements before setting their
location.  That interferes with the design when the new tree or
statement is meant to be a replacement of another.  I fixed a few
cases like that to set the location first but didn't have a way
of finding all such instances.  My expectation was to over time
change GCC to make sure a location would always be set before
the no-warning bit, and asserting that on every call to these
routines.  Adding tests like in the patch below goes in the opposite
direction and effectively papers over the problem.  I can't think
of a way to make the suppression work completely reliably without
ensuring that a location is always set before suppressing
a warning.

Martin

> 
> Thanks,
> Richard.
> 
>> Tested on x86-64/Linux, OK for mainline and 12 branch?
>>
>>
>> 2022-06-10  Eric Botcazou  <ebotcazou@adacore.com>
>>
>>          * gimple.h (gimple_set_location): Do not copy warning data from
>>          the previous location when it is UNKNOWN_LOCATION.
>>
>>
>> 2022-06-10  Eric Botcazou  <ebotcazou@adacore.com>
>>
>> testsuite/
>>          * c-c++-common/nonnull-1.c: Remove XFAIL for C++.
>>
>> --
>> Eric Botcazou
> 

Re: [PATCH] Do not erase warning data in gimple_set_location

[Eric Botcazou]

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> Hmm, I think instead of special-casing UNKNOWN_LOCATION
> what gimple_set_location should probably do is either not copy
> warnings at all or union them.  Btw, gimple_set_location also
> removes a previously set BLOCK (but gimple_set_block preserves
> the location locus and diagnostic override).
> 
> So I'd be tempted to axe the copy_warning () completely here. 

The first thing I tried, but it regressed the original testcase IIRC.

Even my minimal patch manages to break bootstrap on ARM:

buildslave/workspace/tcwg_gnu_1/abe/snapshots/gcc.git~master/libcpp/lex.cc:
1523:9: error: pointer used after ‘void operator delete(void*, std::size_t)’ 
[-Werror=use-after-free]
# 00:31:04 make[3]: *** [Makefile:227: lex.o] Error 1
# 00:31:04 make[2]: *** [Makefile:9527: all-stage3-libcpp] Error 2
# 00:31:35 make[1]: *** [Makefile:25887: stage3-bubble] Error 2
# 00:31:35 make: *** [Makefile:1072: all] Error 2

      /* Don't warn for cases like when a cdtor returns 'this' on ARM.  */
      else if (warning_suppressed_p (var, OPT_Wuse_after_free))
	return;

because warning-control.cc:copy_warning also clobbers the warning data of the 
destination.  We have in cp/decl.cc:maybe_return_this the lines:

      /* Return the address of the object.  */
      tree val = DECL_ARGUMENTS (current_function_decl);
      suppress_warning (val, OPT_Wuse_after_free);

-Wuse-after-free is suppressed for the location of VAL and the TREE_NO_WARNING 
bit set on it.  But other expressions may have the same location as VAL and 
the TREE_NO_WARNING bit _not_ set, so when you call copy_warning (expr, expr) 
(we do that a lot after failed folding) for them, copy_warning erases the 
warning data of the location.

I have installed the obvious fixlet after testing on x86-64/Linux, but the 
decoupling between TREE_NO_WARNING bit and location looks a bit problematic.


	* warning-control.cc (copy_warning) [generic version]: Do not erase
	the warning data of the destination location when the no-warning
	bit is not set on the source.
	(copy_warning) [tree version]: Return early if TO is equal to FROM.
	(copy_warning) [gimple version]: Likewise.
testsuite/
	* g++.dg/warn/Wuse-after-free5.C: New test.

-- 
Eric Botcazou

[-- Attachment #2: p.diff --]
[-- Type: text/x-patch, Size: 1095 bytes --]

diff --git a/gcc/warning-control.cc b/gcc/warning-control.cc
index 0cbb4f079fa..7e9e701cfbe 100644
--- a/gcc/warning-control.cc
+++ b/gcc/warning-control.cc
@@ -191,7 +191,7 @@ void copy_warning (ToType to, FromType from)
 {
   const location_t to_loc = get_location (to);
 
-  bool supp = get_no_warning_bit (from);
+  const bool supp = get_no_warning_bit (from);
 
   nowarn_spec_t *from_spec = get_nowarn_spec (from);
   if (RESERVED_LOCATION_P (to_loc))
@@ -209,7 +209,7 @@ void copy_warning (ToType to, FromType from)
 	  nowarn_spec_t tem = *from_spec;
 	  nowarn_map->put (to_loc, tem);
 	}
-      else
+      else if (supp)
 	{
 	  if (nowarn_map)
 	    nowarn_map->remove (to_loc);
@@ -226,6 +226,8 @@ void copy_warning (ToType to, FromType from)
 void
 copy_warning (tree to, const_tree from)
 {
+  if (to == from)
+    return;
   copy_warning<tree, const_tree>(to, from);
 }
 
@@ -250,5 +252,7 @@ copy_warning (gimple *to, const_tree from)
 void
 copy_warning (gimple *to, const gimple *from)
 {
+  if (to == from)
+    return;
   copy_warning<gimple *, const gimple *>(to, from);
 }

[-- Attachment #3: Wuse-after-free5.C --]
[-- Type: text/x-c++src, Size: 406 bytes --]

// Check the suppression of -Wuse-after-free for destructors on ARM
// { dg-do compile }
// { dg-options "-Wuse-after-free" }

struct range_label {
  virtual ~range_label();
};

struct unpaired_bidi_rich_location {
  struct custom_range_label : range_label {};
  unpaired_bidi_rich_location(int);
  custom_range_label m_custom_label;
};

void maybe_warn_bidi_on_close() { unpaired_bidi_rich_location(0); }

Re: [PATCH] Do not erase warning data in gimple_set_location

[Richard Biener]

On Tue, Jun 14, 2022 at 12:49 PM Eric Botcazou <botcazou@adacore.com> wrote:
>
> > Hmm, I think instead of special-casing UNKNOWN_LOCATION
> > what gimple_set_location should probably do is either not copy
> > warnings at all or union them.  Btw, gimple_set_location also
> > removes a previously set BLOCK (but gimple_set_block preserves
> > the location locus and diagnostic override).
> >
> > So I'd be tempted to axe the copy_warning () completely here.
>
> The first thing I tried, but it regressed the original testcase IIRC.
>
> Even my minimal patch manages to break bootstrap on ARM:
>
> buildslave/workspace/tcwg_gnu_1/abe/snapshots/gcc.git~master/libcpp/lex.cc:
> 1523:9: error: pointer used after ‘void operator delete(void*, std::size_t)’
> [-Werror=use-after-free]
> # 00:31:04 make[3]: *** [Makefile:227: lex.o] Error 1
> # 00:31:04 make[2]: *** [Makefile:9527: all-stage3-libcpp] Error 2
> # 00:31:35 make[1]: *** [Makefile:25887: stage3-bubble] Error 2
> # 00:31:35 make: *** [Makefile:1072: all] Error 2
>
>       /* Don't warn for cases like when a cdtor returns 'this' on ARM.  */
>       else if (warning_suppressed_p (var, OPT_Wuse_after_free))
>         return;
>
> because warning-control.cc:copy_warning also clobbers the warning data of the
> destination.  We have in cp/decl.cc:maybe_return_this the lines:
>
>       /* Return the address of the object.  */
>       tree val = DECL_ARGUMENTS (current_function_decl);
>       suppress_warning (val, OPT_Wuse_after_free);
>
> -Wuse-after-free is suppressed for the location of VAL and the TREE_NO_WARNING
> bit set on it.  But other expressions may have the same location as VAL and
> the TREE_NO_WARNING bit _not_ set, so when you call copy_warning (expr, expr)
> (we do that a lot after failed folding) for them, copy_warning erases the
> warning data of the location.
>
> I have installed the obvious fixlet after testing on x86-64/Linux, but the
> decoupling between TREE_NO_WARNING bit and location looks a bit problematic.

Thanks - that makes more sense.

>
>         * warning-control.cc (copy_warning) [generic version]: Do not erase
>         the warning data of the destination location when the no-warning
>         bit is not set on the source.
>         (copy_warning) [tree version]: Return early if TO is equal to FROM.
>         (copy_warning) [gimple version]: Likewise.
> testsuite/
>         * g++.dg/warn/Wuse-after-free5.C: New test.
>
> --
> Eric Botcazou