On 6/12/19 1:22 PM, Jakub Jelinek wrote:
> On Wed, Jun 12, 2019 at 01:11:09PM +0200, Martin Liška wrote:
>> 2019-06-12 Martin Liska <[email protected]>
>>
>> * calls.c (special_function_p): Make it global.
>> * calls.h (special_function_p): Declare.
>
> Why?
Not needed any longer.
>
>> * tree-cfg.c (do_warn_unused_result): Do not
>> warn for alloca(0).
>> --- a/gcc/tree-cfg.c
>> +++ b/gcc/tree-cfg.c
>> @@ -63,6 +63,7 @@ along with GCC; see the file COPYING3. If not see
>> #include "opts.h"
>> #include "asan.h"
>> #include "profile.h"
>> +#include "calls.h"
>>
>> /* This file contains functions for building the Control Flow Graph (CFG)
>> for a function tree. */
>> @@ -9447,10 +9448,17 @@ do_warn_unused_result (gimple_seq seq)
>> location_t loc = gimple_location (g);
>>
>> if (fdecl)
>> - warning_at (loc, OPT_Wunused_result,
>> - "ignoring return value of %qD "
>> - "declared with attribute %<warn_unused_result%>",
>> - fdecl);
>> + {
>> + if ((special_function_p (fdecl, 0) & ECF_MAY_BE_ALLOCA)
>
> Why not instead gimple_maybe_alloca_call_p (g) ?
Because I was not aware of the function ;)
> On the other side, you want && gimple_call_num_args (g) == 1,
Sure.
> if some alloca call had wrong declaration, you might ICE otherwise.
>
>> + && TREE_CODE (gimple_call_arg (g, 0)) == INTEGER_CST
>> + && wi::to_wide (gimple_call_arg (g, 0)) == 0)
>
> && integer_zerop (gimple_call_arg (g, 0))
>
> instead?
Yep.
>
> Plus you need a comment explaining why we don't warn about alloca with
> constant 0 argument.
Also done.
Is it fine now?
Martin
>
> Jakub
>
>From dfdb688206cadd7fb9450ba005e8aa465ae61f7e Mon Sep 17 00:00:00 2001
From: Martin Liska <[email protected]>
Date: Wed, 12 Jun 2019 12:22:36 +0200
Subject: [PATCH] Do not warn with warn_unused_result for alloca(0).
gcc/ChangeLog:
2019-06-12 Martin Liska <[email protected]>
* tree-cfg.c (do_warn_unused_result): Do not
warn for alloca(0) as it's used by some C
libraries to release previously allocated memory
via alloca calls.
gcc/testsuite/ChangeLog:
2019-06-12 Martin Liska <[email protected]>
* gcc.dg/pr78902.c: Add testing of alloca(0).
* gcc.dg/attr-alloc_size-5.c: Do not warn
about alloca(0).
---
gcc/testsuite/gcc.dg/attr-alloc_size-5.c | 2 +-
gcc/testsuite/gcc.dg/pr78902.c | 1 +
gcc/tree-cfg.c | 18 ++++++++++++++----
3 files changed, 16 insertions(+), 5 deletions(-)
diff --git a/gcc/testsuite/gcc.dg/attr-alloc_size-5.c b/gcc/testsuite/gcc.dg/attr-alloc_size-5.c
index 7aa7cbf0c72..26ee43f87de 100644
--- a/gcc/testsuite/gcc.dg/attr-alloc_size-5.c
+++ b/gcc/testsuite/gcc.dg/attr-alloc_size-5.c
@@ -230,5 +230,5 @@ test_alloca (size_t n)
{
extern void* alloca (size_t);
- alloca (0); /* { dg-warning "ignoring return value of '.*' declared with attribute 'warn_unused_result'" } */
+ alloca (0);
}
diff --git a/gcc/testsuite/gcc.dg/pr78902.c b/gcc/testsuite/gcc.dg/pr78902.c
index 49efc970475..f0f4314d684 100644
--- a/gcc/testsuite/gcc.dg/pr78902.c
+++ b/gcc/testsuite/gcc.dg/pr78902.c
@@ -7,6 +7,7 @@ void foo(void)
__builtin_malloc (1); /* { dg-warning "ignoring return value of '__builtin_malloc' declared with attribute 'warn_unused_result'" } */
__builtin_calloc (10, 20); /* { dg-warning "ignoring return value of '__builtin_calloc' declared with attribute 'warn_unused_result'" } */
__builtin_alloca (10); /* { dg-warning "ignoring return value of '__builtin_alloca' declared with attribute 'warn_unused_result'" } */
+ __builtin_alloca (0);
__builtin_realloc (ptr, 100); /* { dg-warning "ignoring return value of '__builtin_realloc' declared with attribute 'warn_unused_result'" } */
__builtin_aligned_alloc (10, 16); /* { dg-warning "ignoring return value of '__builtin_aligned_alloc' declared with attribute 'warn_unused_result'" } */
__builtin_strdup ("pes"); /* { dg-warning "ignoring return value of '__builtin_strdup' declared with attribute 'warn_unused_result'" } */
diff --git a/gcc/tree-cfg.c b/gcc/tree-cfg.c
index a585efea3d8..0d21f3624d7 100644
--- a/gcc/tree-cfg.c
+++ b/gcc/tree-cfg.c
@@ -63,6 +63,7 @@ along with GCC; see the file COPYING3. If not see
#include "opts.h"
#include "asan.h"
#include "profile.h"
+#include "calls.h"
/* This file contains functions for building the Control Flow Graph (CFG)
for a function tree. */
@@ -9447,10 +9448,19 @@ do_warn_unused_result (gimple_seq seq)
location_t loc = gimple_location (g);
if (fdecl)
- warning_at (loc, OPT_Wunused_result,
- "ignoring return value of %qD "
- "declared with attribute %<warn_unused_result%>",
- fdecl);
+ {
+ /* Some C libraries use alloca(0) in order to free previously
+ allocated memory by alloca calls. */
+ if (gimple_maybe_alloca_call_p (g)
+ && gimple_call_num_args (g) == 1
+ && integer_zerop (gimple_call_arg (g, 0)))
+ ;
+ else
+ warning_at (loc, OPT_Wunused_result,
+ "ignoring return value of %qD declared "
+ "with attribute %<warn_unused_result%>",
+ fdecl);
+ }
else
warning_at (loc, OPT_Wunused_result,
"ignoring return value of function "
--
2.21.0
