[LLVMdev] Dependence Analysis [was: Flow-Sensitive AA]

Julio julio.martin.hidalgo at gmail.com
Thu Aug 28 00:31:06 PDT 2008

Hello, I was pretending to make a little memory dependence analysis
following "Optimizing compilers for modern architectures", but I've found a
little problem.

I don't know how to infer the array subscripting from the GEP instruction.

for (i1 = 0; i1 < N1; ++i1)
  for (i2 = 0; i2 < N2; ++i2)

At first I though to obtain the chain recurrence:

(pointer to A) + alpha1*i1 + alpha2*i2 + ...

And suppose that the major alpha corresponds to the first subscript, and so

But, this is only making permutations, if I have something a little more

A = [10][10];

for (i = 0; i < 10; ++i)
  for (j = 0; j < 10; ++j)

I would have: (pointer to A) + 10 - i + 10j


for (i = 0; i < 10; ++i)
  for (j = 0; j < 10; ++j)

(pointer to A) + i -9j

Etc, etc..... Well, in conclusion, how did you minded to highering gep to
array subscripting, or there is another dependence analysis that doesn't
make necessary splitting subscripts?
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