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[Arushi Aggarwal <arushi987 AT gmail.com>]

Ah.  I think I understand what your concern is now, Tarek.  You are worried that what you are seeing below when you print out the DSNodes means that a single SSA value has been mapped to multiple DSNodes.  Is this correct?

The strings below are not printing out the mapping between SSA values and DSNodes.  That information is not even contained within DSNode objects.  Rather, each DSGraph object has an object called the ScalarMap.  The ScalarMap tracks the mapping of SSA values to DSNodes.  If you want to see which SSA values points to which DSNode, you'll need to print out the DSGraphs by using opt's -analyze option when running DSA (it should create one GraphViz .dot file for every DSGraph).

Looking at the code that prints DSNodes, I believe it looks to see if the DSNode represents one or more global variables and prints the leader of the global EC for that SSA value (remember that DSA puts globals into equivalence classes to reduce the size of the ScalarMap in each DSGraph).  So, I believe what the @G2 in the DSNodes is saying is that the DSNode represents the global variable G2 (i.e., the DSNode represents the global value pointed to by @G2) and that G2's global EC contains 1 global.

Actually @G2+1EC means that G2s global EC contains G2 and another value(in this case G1). 

Arushi, does the above sound correct?

So, in short, if you want to see if buildDSNodeEquivs is working properly, print the DSGraphs to understand what SSA values are pointing to which DSNodes and then see if the right DSNodes are put into the same equivalence classes by buildsDSNodeEquivs.  Don't look at DSNodes to see which SSA values are pointing to them because the DSNode doesn't have that information.

-- John T.

Regards,

Tarek


On Fri, Feb 18, 2011 at 11:13 PM, Arushi Aggarwal<arushi987 AT gmail.com>  wrote:

Hi,
I am not sure what your buildDSNodeEquivs method is. If you can tell me that
I can try
looking at this.
Arushi

On Fri, Feb 18, 2011 at 10:10 PM, Tarek Chammah<tchammah AT uwaterloo.ca>
wrote:

Hi, this issue is possibly a blocker for me.  I'm utilizing DSA to
garner points-to information.  After the top down pass is run and the
buildDSNodeEquivs method is executed to place DSNodes between callers
and callees into their equivalence classes I get rather strange
output.  Using a simple test I dump the nodes in the resulting
equivalence classes.  What I get is a pair of distinct nodes in the
ECs that contain the same program variable/value location information.
 I don't understand why this information is repeated.

Eg. I get this, two ECs each containing a pair with repeated
information (about G2 and the string constant):
Node0x1008870 [shape=record,shape=Mrecord,label="{i32: GR\n@G2 + 1
EC\n|{<s0>|<s1>|<s2>|<s3>}}"];
Node0xff4950 [shape=record,shape=Mrecord,label="{i32: GR\n@G2 + 1
EC\n|{<s0>|<s1>|<s2>|<s3>}}"];

Node0x1008af0 [shape=record,shape=Mrecord,label="{i8 array:
GR\n@.str\n|{<s0>}}"];
Node0xff4d50 [shape=record,shape=Mrecord,label="{i8 array:
GR\n@.str\n|{<s0>}}"];

For this sample program:
#include<stdio.h>

int G1 = 4, G2 = 3;
int *XX, *YY;

int main() {
      XX =&G1;
      YY = XX;
      YY =&G2;
      XX =&G2;
      if (*XX>*YY) printf("Not possible!\n");
      return 0;
}


Thanks,

Tarek

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