Improve/fix array/pointer support in dizy #4
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…core Previously, dizy only took into account variable initialization for integer variables. Extend this to pointer variables, as in SCORE, in order for array parameters to be correctly aliased.
dizy handles array access by discriminating against the type of the lvalue
and the rvalue, and checking whether they are pointer types.
However, LLVM makes a distinction between pointer values (int *foo) and array
values (int foo[2]). Therefore, on the following piece of code:
int foo[2];
foo[x] = 42;
dizy would lead to the following nonsensical interpretation:
{ foo - 42 = 0 }
instead of:
{ update( foo , idx ) - 42 = 0
idx - 2 = 0 }
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Hi,
There are a few issues preventing dizy from working correctly with arrays.
Thus, dizy cannot infer any meaningful relation between accesses of the same input array in the original and modified version of the program, thus badly affecting dizy's precision when one of the input parameters is a pointer. This is fixed in the first commit by extending initial value handling to pointer values, as it is done in SCORE.
On a side note, “ccc” may produce incorrect correlating programs by aliasing pointers from the original version and the modified version together. While it might be mitigated by dizy's rules (I haven't checked yet), it is still a fundamental issue with “ccc”. This is not a fundamental problem with SCORE (I haven't checked how the implementation handles it, though).