From: Eric Botcazou <botcazou@adacore.com>
To: Richard Biener <richard.guenther@gmail.com>
Cc: Martin Sebor <msebor@redhat.com>,
gcc-patches@gcc.gnu.org, GCC Patches <gcc-patches@gcc.gnu.org>
Subject: Re: [PATCH] Do not erase warning data in gimple_set_location
Date: Tue, 14 Jun 2022 12:49:40 +0200 [thread overview]
Message-ID: <2514895.Lt9SDvczpP@fomalhaut> (raw)
In-Reply-To: <CAFiYyc0QhXatqni3ibge8aBzPp29niBsPeXYv1qpzhBN+6UwPQ@mail.gmail.com>
[-- Attachment #1: Type: text/plain, Size: 2266 bytes --]
> 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); }
next prev parent reply other threads:[~2022-06-14 10:49 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-10 10:57 Eric Botcazou
2022-06-12 15:38 ` Jeff Law
2022-06-13 11:15 ` Richard Biener
2022-06-13 15:39 ` Martin Sebor
2022-06-14 10:49 ` Eric Botcazou [this message]
2022-06-14 13:33 ` Richard Biener
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