This is again motivated by D67122 sanitizer check enhancement.
That patch seemingly worsens -fsanitize=pointer-overflow
overhead from 25% to 50%, which strongly implies missing folds.
This pattern isn't exactly what we get there
(strict vs. non-strict predicate), but this pattern does not
require known-bits analysis, so it is best to handle it first.
Name: 0 %adjusted = add i8 %base, %offset %not_null = icmp ne i8 %adjusted, 0 %no_underflow = icmp ule i8 %adjusted, %base %r = and i1 %not_null, %no_underflow => %neg_offset = sub i8 0, %offset %r = icmp ugt i8 %base, %neg_offset
There are 3 other variants of this pattern,
they all will go into InstSimplify: