[llvm-dev] Using isConfused() method for LLVM Dependence Analysis

Chatterjee, Bodhisatwa via llvm-dev llvm-dev at lists.llvm.org
Fri Jun 14 09:24:41 PDT 2019


I am trying to find out instances of confused dependencies in my program. According to LLVM's doxygen page, 'confused dependencies' are detected by function isConfused() - Returns true if this dependence is confused (the compiler understands nothing and makes worst-case assumptions) (http://llvm.org/doxygen/classllvm_1_1Dependence.html#a5c65e22ef4b0368ab040d1bd4ead382d)

For the following code snippet:

  for (int i = 0; i < 10; i++)
       a = 1;
       for (int j = 0; j < 9; j++)
             b = 2;
             for (int k = 0; k < 8; k++)
                     c = 3;
We are constructing dependencies between the corresponding IR of the above code and checking whether it is confused or not:

  store i32 1, i32* @a, align 4
  store i32 2, i32* @b, align 4
Confused Dependence or Not: 1

Since the variables 'a' and 'b' are in different memory locations, why is LLVM's isConfused method gives us True?
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