[PATCH v3 1/2] [PR debug/67192] Fix C loops' back-jump location

Andreas Arnez arnez@linux.vnet.ibm.com
Thu Nov 5 15:30:00 GMT 2015


On Thu, Nov 05 2015, Bernd Schmidt wrote:

> On 11/05/2015 12:33 PM, Andreas Arnez wrote:
>
>> Thanks again for reviewing.  Are you going to look at patch #2 as well?
>
> Yeah, still thinking about that one.
>
>>> Does C++ have similar issues?
>>
>> Not this particular issue, AFAIK.  But I've just looked at how C++ fares
>> with the enhanced version of pr67192.c from patch #2.  There I see the
>> following:
>>
>>    Breakpoint 2, f4 () at pr67192.cc:54
>>    (gdb) p cnt
>>    $1 = 16
>>
>> I.e., when breaking on "while (1)" the first loop iteration has already
>> executed.  This is because the C++ parser assigns the backward-goto to
>> the 'while' token.  It's the same issue you pointed at with version 2 of
>> my patch.
>>
>> Shall I open a bug for that?
>
> I'd obviously prefer if you'd manage to get the two frontends behave
> identically. The alternative would be to open a bug.

OK, I guess it depends on whether we want to go the route of patch #2.
If so, it seems we can do the same for the C++ parser, like in the patch
below.  Note that I've not tested this very much.

-- >8 --
Subject: [PATCH] C++: Fix location of loop statement

---
 gcc/cp/cp-gimplify.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/cp-gimplify.c b/gcc/cp/cp-gimplify.c
index e4b50e5..d9bb708 100644
--- a/gcc/cp/cp-gimplify.c
+++ b/gcc/cp/cp-gimplify.c
@@ -266,7 +266,12 @@ genericize_cp_loop (tree *stmt_p, location_t start_locus, tree cond, tree body,
 	loop = stmt_list;
     }
   else
-    loop = build1_loc (start_locus, LOOP_EXPR, void_type_node, stmt_list);
+    {
+      location_t loc = EXPR_LOCATION (expr_first (body));
+      if (loc == UNKNOWN_LOCATION)
+	loc = start_locus;
+      loop = build1_loc (loc, LOOP_EXPR, void_type_node, stmt_list);
+    }
 
   stmt_list = NULL;
   append_to_statement_list (loop, &stmt_list);
-- 
2.3.0



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