2012/1/10 Richard Guenther <[email protected]>:
> On Tue, Jan 10, 2012 at 10:58 AM, Kai Tietz <[email protected]> wrote:
>> Ping
>>
>> 2012/1/8 Kai Tietz <[email protected]>:
>>> Hi,
>>>
>>> this patch makes sure that for increment of
>>> postfix-increment/decrement we use also orignal lvalue instead of tmp
>>> lhs value for increment. This fixes reported issue about sequence
>>> point in PR/48814
>>>
>>> ChangeLog
>>>
>>> 2012-01-08 Kai Tietz <[email protected]>
>>>
>>> PR middle-end/48814
>>> * gimplify.c (gimplify_self_mod_expr): Use for
>>> postfix-inc/dec lvalue instead of temporary
>>> lhs.
>>>
>>> Regression tested for x86_64-unknown-linux-gnu for all languages
>>> (including Ada and Obj-C++). Ok for apply?
>>>
>>> Regards,
>>> Kai
>>>
>>> Index: gimplify.c
>>> ===================================================================
>>> --- gimplify.c (revision 182720)
>>> +++ gimplify.c (working copy)
>>> @@ -2258,7 +2258,7 @@
>>> arith_code = POINTER_PLUS_EXPR;
>>> }
>>>
>>> - t1 = build2 (arith_code, TREE_TYPE (*expr_p), lhs, rhs);
>>> + t1 = build2 (arith_code, TREE_TYPE (*expr_p), lvalue, rhs);
>>>
>>> if (postfix)
>>> {
Hi Richard,
> Please add testcases. Why does your patch make a difference?
> lhs is just the gimplified lvalue.
yes, exactly this makes a big difference for post-inc/dec. I show you
gimple-dump to illustrate this in more detail. I used here -O2 option
with using attached patch.
gcc without that patch produces following gimple for main:
main ()
{
int count.0;
int count.1;
int D.2721;
int D.2725;
int D.2726;
count.0 = count; <-- here we store orginal value 'count' for having
array-access-index
D.2721 = incr (); <- within that function count gets modified
arr[count.0] = D.2721;
count.1 = count.0 + 1; <- Here happens the issue. We increment the
saved value of 'count'
count = count.1; <- By this the modification of count in incr() gets void.
...
By the change we make sure to use count's value instead its saved temporary.
Patched gcc produces this gimple:
main ()
{
int count.0;
int count.1;
int D.1718;
int D.1722;
int D.1723;
count.0 = count;
D.1718 = incr ();
arr[count.0] = D.1718;
count.0 = count; <-- Reload count.0 for post-inc/dec to use count's
current value
count.1 = count.0 + 1;
count = count.1;
count.0 = count;
Ok, here is the patch with adusted testcase from PR.
ChangeLog
2012-01-10 Kai Tietz <[email protected]>
PR middle-end/48814
* gimplify.c (gimplify_self_mod_expr): Use for
postfix-inc/dec lvalue instead of temporary lhs.
Regression tested for all languages (including Ada and Obj-C++). Ok for apply?
Regards,
Kai
2012-01-10 Kai Tietz <[email protected]>
* gcc.c-torture/execute/pr48814.c: New test.
Index: gcc/gcc/gimplify.c
===================================================================
--- gcc.orig/gcc/gimplify.c
+++ gcc/gcc/gimplify.c
@@ -2258,7 +2258,7 @@ gimplify_self_mod_expr (tree *expr_p, gi
arith_code = POINTER_PLUS_EXPR;
}
- t1 = build2 (arith_code, TREE_TYPE (*expr_p), lhs, rhs);
+ t1 = build2 (arith_code, TREE_TYPE (*expr_p), lvalue, rhs);
if (postfix)
{
Index: gcc/gcc/testsuite/gcc.c-torture/execute/pr48814.c
===================================================================
--- /dev/null
+++ gcc/gcc/testsuite/gcc.c-torture/execute/pr48814.c
@@ -0,0 +1,18 @@
+extern void abort (void);
+
+int arr[] = {1,2,3,4};
+int count = 0;
+
+int __attribute__((noinline))
+incr (void)
+{
+ return ++count;
+}
+
+int main()
+{
+ arr[count++] = incr ();
+ if (count != 2 || arr[count] != 3)
+ abort ();
+ return 0;
+}
