Plotscop

The LLVM's polyhedral optimizer Polly has the ability to export static control parts (SCOPs) as JSON files. It can also import user modified SCOPs in the JSON format and generate code for them instead of the ones the default optimizer built. This is a really useful feature if you want to play with polyhedral optimization.

Unfortunately, if you are not yet expierienced in the polyhedral optimization, understanding what a JSCOP actually means can be quite hard. The goal of this tool is to help you with that by creating a visual representation of the SCOP in the form of an animation that shows which memory locations are accessed at what time.

Example

This code

int* A = (int*) malloc(arraysize*sizeof(int));
int* B = (int*) malloc(arraysize*sizeof(double));

memset(&A[0], 0, arraysize*sizeof(int));

for(int i=0; i<arraysize-4; i++) {
	B[42] += A[i+2];
}

printf("sum=%d\n", B[42]);

will produce the following JSCOP when compiled with a debug-build of llvm (if you use a regular release build the variable names are mostly replaced by numbers in order to save space, but it works the same way):

{
   "context" : "{  :  }",
   "name" : "for.body => for.end",
   "statements" : [
      {
         "accesses" : [
            {
               "kind" : "read",
               "relation" : "{ Stmt_for_body[i0] -> MemRef_call[2 + i0] }"
            },
            {
               "kind" : "read",
               "relation" : "{ Stmt_for_body[i0] -> MemRef_call1[42] }"
            },
            {
               "kind" : "write",
               "relation" : "{ Stmt_for_body[i0] -> MemRef_call1[42] }"
            }
         ],
         "domain" : "{ Stmt_for_body[i0] : i0 >= 0 and i0 <= 95 }",
         "name" : "Stmt_for_body",
         "schedule" : "{ Stmt_for_body[i0] -> [i0] : i0 >= 0 and i0 <= 95 }"
      }
   ]
}

You can visualize this as an ASCII art animation with ./plotscop pollyoutput.jscop

It will look something like this:

You can produce an animated gif like the one above with a patched version of ansi2gif (https://github.com/tim0s/ansi2gif):

./plotscop foo.jscop > foo.ans
.ansi2gif --xsize 160 --ysize=10 --animate --frameperrefresh foo.ans foo.gif