C++: Handle overflow for upperbound #6745

I was able to construct a test case to show that the unsound treatment of overflow was not introduced with #6568 but existed already:

void test_overflow() {
  unsigned int x = 0xffFFffFF;
  if ((x + 256) <= 512) {
    out(x); // range analysis says upper bound is 256
  }
}

The existing problem is much harder to solve than the amplification of it that got introduced with #6568. That's because we haven't calculated overflow information yet at the point where we determine what to do with guard phi nodes. The only general solution I can think of is to make linearAccessImpl much more conservative around unsigned arithmetic.

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C++: Handle overflow for upperbound #6745

C++: Handle overflow for upperbound #6745

andersfugmann commented Sep 24, 2021

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jbj commented Sep 27, 2021

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