xazax.hun added a comment.
In D78457#1991780 <https://reviews.llvm.org/D78457#1991780>, @martong wrote:
> If a symbol is unused and garbage collected then that is not part of the path
> constraint that leads to the ErrorNode, is it? So why should we care about
> constraints on an unused symbol?
Unused means it is unused at a program point.
For example:
void f(int sym1, int sym2) {
int sym3 = sym1 * sym2;
if (!sym1)
return;
// Here sym1 is no longer used, it is garbage collected from the state.
if (sym3) {
sym2 / 0; // This is a false positive. sym1 is 0 -> sym3 should be 0 as
well, this branch is never taken. But to refute this path we need the info
about sym1, that is not available in the ErrorNode state. It was garbage
collected earlier.
}
}
I did not try this specific example. The constraint manager might be smart
enough to not to report a false positive, but I hope it makes the idea clear
why do we need the garbage collected symbols.
Repository:
rG LLVM Github Monorepo
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