[PATCH] Update source location for PRE inserted stmt

[Xinliang David Li]

Dehao's patch will make the debugging of the following code (-g -O2)
less jumpy.   After the testing of x > 0, it should go to line 'a++'.
 Without the fix, when stepping through 'abc', the lines covered are
6, 4, 11, 13. With the fix it should be 6, 9, 11, 13 -- much better.

David




1. int x;

2. __attribute__((noinline)) int abc (int *a)
3. {
4.  int ret = 0;
5.
6.  if (x > 0)
7.    ret += *a;
8.  else
9.    a++;
10.
11.  ret += *a;
12.  return ret;
13 }


int main()
{
  int a = 0;

   x = -1;
   return abc ( &a);

}

On Wed, Oct 31, 2012 at 2:34 AM, Richard Biener
<richard.guenther@gmail.com> wrote:
> On Wed, Oct 31, 2012 at 12:57 AM, Xinliang David Li <davidxl@google.com> wrote:
>> It will make the location info for the newly synthesized stmt more
>> deterministic, I think.
>
> Maybe, but it will increase the jumpiness in the debugger without actually
> being accurate, no?  For example if the partially redundant expression is
>
>   i + j;
>
> then when computed at the insertion point the values of i and j do not
> necessarily reflect the computed value!  Instead we may compute the
> result of i + j using completely different components / operation.
>
> Thus I think inserted expressions should not have any debug information
> at all because they do not correspond to a source line.
>
> Richard.
>
>> David
>>
>> On Tue, Oct 30, 2012 at 4:38 PM, Steven Bosscher <stevenb.gcc@gmail.com> wrote:
>>> On Wed, Oct 31, 2012 at 12:00 AM, Dehao Chen wrote:
>>>> This patch aims to improve debugging of optimized code. It ensures
>>>> that PRE inserted statements have the same source location as the
>>>> statement at the insertion point, instead of UNKNOWN_LOCATION.
>>>
>>> Wrong patch attached.
>>>
>>> However, is it really better to have the location of the insertion
>>> point than to have UNKNOWN_LOCATION? It's not where the value is
>>> computed in the source program...
>>>
>>> Ciao!
>>> Steven