[PATCH] D74943: [GISel][KnownBits] Add a cache mechanism to speed compile time

[Quentin Colombet via Phabricator via llvm-commits]

qcolombet created this revision.
qcolombet added reviewers: aemerson, paquette, volkan, aditya_nandakumar, dsanders, arsenm.
Herald added subscribers: hiraditya, wdng.
Herald added a project: LLVM.

This patch adds a cache that is valid only for the duration of a call
to getKnownBits. With such short lived cache we avoid all the problems
of cache invalidation while still getting the benefits of reusing
the information we already computed.

This cache is useful whenever an instruction occurs more than once
in a chain of computation.
E.g.,
v0 = G_ADD v1, v2
v3 = G_ADD v0, v1

Previously we would compute the known bits for:
v1, v2, v0, then v1 again and finally v3.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D74943

Files:
  llvm/include/llvm/CodeGen/GlobalISel/GISelKnownBits.h
  llvm/lib/CodeGen/GlobalISel/GISelKnownBits.cpp

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