Re: [creduce-dev] reduction using dynamic information

[Yang Chen <chenyang@cs.utah.edu>]

Hi John,

On 2016-07-11 15:21, John Regehr wrote:
> So what I'm looking for is an easy way to enumerate the expressions in
> a C/C++ compilation unit and then, for the specified one, rewrite the
> program so that the first value taken on by that expression is printed
> out. The other thing we need is to replace the expression with its
> value -- creating a C-Reduce variant that can be run through the
> interestingness test.

Let me try to hack it up this week. I will make this new transformation 
follow our existing convention: it will process the expression based on 
the counter value passed from the command line. For now, I may put the 
following restrictions on the transformation:

  (1) restrict it on C programs;
  (2) print out the value of the expression only if the expression is of 
integer or float type (e.g., char, int, float, double, etc);
  (3) a new local variable will be created for each expression of 
interest;

Item (3) may need more explanation. Assume that we have the following 
code snippet (where expr1 is of type int):

  x = foo(expr1, expr2);

the transformation would turn the code into something like:

  { int tmp1 = expr1;
    printf("%d\n", tmp1);
    x = foo(tmp1, expr2);}

The reason is that expr1 may have side-effect. To make the 
transformation have as little impact as possible on the original 
semantic, expr1 should only be executed once (note that we may still 
change the original semantics because expr2 can be executed before expr1 
for the unmodified code).

Once we have the value for tmp1, we can use the following command to 
replace the expr1 with the value:

  $ clang_delta --transformation=replace-expr --counter=1 --value=123 
foo.c

With this command, we would get:

  x = foo(123, expr2);

Can you check if my description meets the requirement? Thanks.

- Yang