dcoughlin added a comment.
It still seems like we are inferring invariants that are not sound. Do we need
to restrict the symbolic transformation so that it only applies when A - B,
too, is known to not overflow? Is that sufficient? Is it often the case that
the analyzer knows these restrictions?
For example, in the following we infer `B - A` is in `[127, 127]` at program
point (1) but, for example, this invariant is not true when `A` is `-100` and
`B` is `40`,
void bar(signed char A, signed char B) {
if (A + 127 < B + 1) {
// (1)
}
}
Similarly we infer `A - B` is in `[0, 127]` at program point (2) but, for
example, this invariant is not true when `A` is `100` and `B` is `-40`,
void foo(signed char A, signed char B) {
if (A + 0 >= B + 0) {
// (2)
}
}
You can see these invariants by running with the 'debug.ViewExplodedGraph'
checker enabled.
https://reviews.llvm.org/D35109
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