AliasSetTracker has special case handling for memset, memcpy and memmove which pre-existed argmemonly on functions and readonly and writeonly on arguments. This patch generalizes it using the AA infrastructure to any call correctly annotated.
The motivation here is to cut down on confusion, not performance per se. For most instructions, there is a direct mapping to alias set. However, this is not guaranteed by the interface and was not in fact true for these three intrinsics *and only these three intrinsics*. I kept getting myself confused about this invariant, so I figured it would be good to clearly distinguish between a instructions and alias sets. Calls happened to be an easy target.
The nice side effect is that custom implementations of memset/memcpy/memmove - including wrappers discovered by IPO - can now be optimized the same as builts by LICM.
Note: The actual removal of the memset/memtransfer specific handling will happen in a follow on NFC patch. It was originally part of this one, but separate for ease of review and rebase.
Differential Revision: https://reviews.llvm.org/D50730
llvm-svn: 341713
Summary:
Currently, in LICM, we use the alias set tracker to identify if the
instruction (we're interested in hoisting) aliases with instruction that
modifies that memory location.
This patch adds an LICM alias analysis diagnostic tool that checks the
mod ref info of the instruction we are interested in hoisting/sinking,
with every instruction in the loop. Because of O(N^2) complexity this
is now only a diagnostic tool to show the limitation we have with the
alias set tracker and is OFF by default.
Test cases show the difference with the diagnostic analysis tool, where
we're able to hoist out loads and readonly + argmemonly calls from the
loop, where the alias set tracker analysis is not able to hoist these
instructions out.
Reviewers: reames, mkazantsev, fedor.sergeev, hfinkel
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D50854
llvm-svn: 340026
We know that an argmemonly function can only access memory pointed to by it's pointer arguments. Rather than needing to consider all possible stores as aliasing (as we do for a readonly function), we can only consider the aliasing of the pointer arguments.
Note that this change only addresses hoisting. I'm thinking about how to address speculation safety as well, but that will be a different change.
FYI, argmemonly disallows accessing memory through non-pointer typed arguments.
Differential Revision: http://reviews.llvm.org/D12771
llvm-svn: 248220
Philip Reames