Summary:
Backends should fold the subtraction into the comparison, but not all
seem to. Moreover, on targets where pointers are not integers, such as
CHERI, an integer subtraction is not appropriate. Instead we should just
compare the two pointers directly, as this should work everywhere and
potentially generate more efficient code.
Reviewers: bogner, lebedev.ri, efriedma, t.p.northover, uweigand, sunfish
Reviewed By: lebedev.ri
Subscribers: dschuff, sbc100, arichardson, jgravelle-google, hiraditya, aheejin, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D74454
This fixes PR22248 on s390x. The previous attempt at this was D19101,
which was before LOAD_STACK_GUARD existed. Compared to the previous
version, this always emits a rather ugly block of 4 instructions, involving
a thread pointer load that can't be shared with other potential users.
However, this is necessary for SSP - spilling the guard value (or thread
pointer used to load it) is counter to the goal, since it could be
overwritten along with the frame it protects.
Differential Revision: http://reviews.llvm.org/D19363
llvm-svn: 267340
James Clarke