Use separate variable for adjusted scale used for GCD computations. This
fixes an issue where we incorrectly determined that all indices are
non-negative and returned noalias because of that.
Follow up to 91fa3565da.
(V * Scale) % X may not produce the same result for any possible value
of V, e.g. if the multiplication overflows. This means we currently
incorrectly determine NoAlias in some cases.
This patch updates LinearExpression to track whether the expression
has NSW and uses that to adjust the scale used for alias checks.
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D99424
While explicit sext instructions were handled correctly, the
implicit sext that occurs if the offset is smaller than the
pointer size blindly assumed that sext(X * Scale + Offset) is the
same as sext(X) * Scale + Offset, which is obviously not correct.
Fix this by extracting the code that handles linear expression
extension and reusing it for the implicit sext as well.
This patch adds a few test cases where currently NoAlias is returned,
but the pointers can alias if the multiply overflows while computing
a GEP index value.
Florian Hahn