On 07/21/16 09:09, Richard Biener wrote:
> On Wed, 20 Jul 2016, Bernd Edlinger wrote:
>
>> On 07/20/16 20:08, Richard Biener wrote:
>>> On July 20, 2016 6:54:48 PM GMT+02:00, Bernd Edlinger
>>> <bernd.edlin...@hotmail.de> wrote:
>>>>
>>>> But I think that alloca just should not be recognized by name any
>>>> more.
>>>
>>> It was introduced to mark calls that should not be duplicated by inlining
>>> or unrolling to avoid increasing stack usage too much. Sth worthwhile to
>>> keep even with -ffreestanding.
>>>
>>> Richard.
>>>
>>
>> On second thought I start to think that an external alloca function
>> might still work. And returning ECF_MAY_BE_ALLOCA just based on the
>> name could be made safe by checking the malloc attribute at the right
>> places.
>>
>> With this new incremental patch the example
>>
>> extern "C"
>> void *alloca(unsigned long);
>> void bar(unsigned long n)
>> {
>> char *x = (char*) alloca(n);
>> if (x)
>> *x = 0;
>> }
>>
>> might actually work when -ansi is used,
>> i.e. it does no longer assume that alloca cannot return null,
>> but still creates a frame pointer, which it would not have done
>> for allocb for instance.
>>
>> But the built-in alloca is still recognized because the builtin
>> does have ECF_MAY_BE_ALLOCA and ECF_MALLOC.
>>
>>
>> Is it OK for trunk after boot-strap and reg-testing?
>
> Hmm, but ECF_MALLOC doesn't guarantee non-NULL return. I think the
> two calls you patched simply shouldn't use the predicates (which
> are misnamed as they check for _maybe_alloca_call_p). Instead they
> have to check for the respective builtins (BUILT_IN_ALLOCA,
> BUILT_IN_ALLOCA_WITH_ALIGN).
>
Yes, I agree. The name should really be gimple_maybe_alloca_call_p if
we are just guessing.
How about this updated patch?
Is it OK for trunk after boot-strap and reg-testing?
Thanks
Bernd.
> Richard.
>
>>
>> Thanks
>> Bernd.
>>
>
2016-07-21 Bernd Edlinger <bernd.edlin...@hotmail.de>
PR middle-end/71876
* calls.c (gimple_maybe_alloca_call_p): New function. Return true
if STMT may be an alloca call.
(gimple_alloca_call_p, alloca_call_p): Return only true for the
builtin alloca call.
* calls.h (gimple_maybe_alloca_call_p): New function.
* tree-inline.c (inline_forbidden_p_stmt): Use
gimple_maybe_alloca_call_p here.
Index: gcc/calls.c
===================================================================
--- gcc/calls.c (revision 238584)
+++ gcc/calls.c (working copy)
@@ -617,10 +617,10 @@ setjmp_call_p (const_tree fndecl)
}
-/* Return true if STMT is an alloca call. */
+/* Return true if STMT may be an alloca call. */
bool
-gimple_alloca_call_p (const gimple *stmt)
+gimple_maybe_alloca_call_p (const gimple *stmt)
{
tree fndecl;
@@ -634,16 +634,44 @@ bool
return false;
}
-/* Return true when exp contains alloca call. */
+/* Return true if STMT is a builtin alloca call. */
bool
+gimple_alloca_call_p (const gimple *stmt)
+{
+ tree fndecl;
+
+ if (!is_gimple_call (stmt))
+ return false;
+
+ fndecl = gimple_call_fndecl (stmt);
+ if (fndecl && DECL_BUILT_IN_CLASS (fndecl) == BUILT_IN_NORMAL)
+ switch (DECL_FUNCTION_CODE (fndecl))
+ {
+ case BUILT_IN_ALLOCA:
+ case BUILT_IN_ALLOCA_WITH_ALIGN:
+ return true;
+ }
+
+ return false;
+}
+
+/* Return true when exp contains a builtin alloca call. */
+
+bool
alloca_call_p (const_tree exp)
{
tree fndecl;
if (TREE_CODE (exp) == CALL_EXPR
&& (fndecl = get_callee_fndecl (exp))
- && (special_function_p (fndecl, 0) & ECF_MAY_BE_ALLOCA))
- return true;
+ && DECL_BUILT_IN_CLASS (fndecl) == BUILT_IN_NORMAL)
+ switch (DECL_FUNCTION_CODE (fndecl))
+ {
+ case BUILT_IN_ALLOCA:
+ case BUILT_IN_ALLOCA_WITH_ALIGN:
+ return true;
+ }
+
return false;
}
Index: gcc/calls.h
===================================================================
--- gcc/calls.h (revision 238584)
+++ gcc/calls.h (working copy)
@@ -23,6 +23,7 @@ along with GCC; see the file COPYING3. If not see
extern int flags_from_decl_or_type (const_tree);
extern int call_expr_flags (const_tree);
extern int setjmp_call_p (const_tree);
+extern bool gimple_maybe_alloca_call_p (const gimple *);
extern bool gimple_alloca_call_p (const gimple *);
extern bool alloca_call_p (const_tree);
extern bool must_pass_in_stack_var_size (machine_mode, const_tree);
Index: gcc/tree-inline.c
===================================================================
--- gcc/tree-inline.c (revision 238584)
+++ gcc/tree-inline.c (working copy)
@@ -3577,7 +3577,7 @@ inline_forbidden_p_stmt (gimple_stmt_iterator *gsi
RAM instead of 256MB. Don't do so for alloca calls emitted for
VLA objects as those can't cause unbounded growth (they're always
wrapped inside stack_save/stack_restore regions. */
- if (gimple_alloca_call_p (stmt)
+ if (gimple_maybe_alloca_call_p (stmt)
&& !gimple_call_alloca_for_var_p (as_a <gcall *> (stmt))
&& !lookup_attribute ("always_inline", DECL_ATTRIBUTES (fn)))
{
