This option was added a while back, to help improve AA around pointer
phi loops. It looks for phi(gep(phi, const), x) loops, checking if x can
then prove more precise aliasing info.
Differential Revision: https://reviews.llvm.org/D82998
As shown in D82998, the basic-aa-recphi option can cause miscompiles for
gep's with negative constants. The option checks for recursive phi, that
recurse through a contant gep. If it finds one, it performs aliasing
calculations using the other phi operands with an unknown size, to
specify that an unknown number of elements after the initial value are
potentially accessed. This works fine expect where the constant is
negative, as the size is still considered to be positive. So this patch
expands the check to make sure that the constant is also positive.
Differential Revision: https://reviews.llvm.org/D83576
This option was added a while back, to help improve AA around pointer
phi loops. It looks for phi(gep(phi, const), x) loops, checking if x can
then prove more precise aliasing info.
Differential Revision: https://reviews.llvm.org/D82998
With the option -basic-aa-recphi we can detect recursive phis that loop
through constant geps, which allows us to detect more no-alias case for
pointer IV's. If the other phi operand and the other alias value are
MustAlias though, we cannot presume that every element in the loop is
also MustAlias. We need to instead be conservative and return MayAlias.
Differential Revision: https://reviews.llvm.org/D82987
David Green