[PATCH] D83884: GlobalISel: Make type for lower action more consistently optional

[Matt Arsenault via Phabricator via llvm-commits]

arsenm created this revision.
arsenm added reviewers: aemerson, dsanders, paquette, aditya_nandakumar, Petar.Avramovic, foad, mbrkusanin.
Herald added subscribers: hiraditya, rovka, wdng.
Herald added a project: LLVM.

Some of the lower implementations were relying on this, however the
type was not set depending on which form .lower* helper form you were
using. For instance, if you used an unconditonal lower(), the type was
never set. Most of the lower actions do not benefit from a type
parameter, and just expand in terms of the original operation's types.

      

However, some lowerings could benefit from an additional type hint to
combine a promotion and an expansion. An example of this is for
add/sub sat. The DAG integer legalization tries to use smarter
expansions directly when promoting the integer type, and doesn't always
produce the same instruction with a wider type.

      

Treat this as an optional hint argument, that only means something for
 specific lower actions. It may be useful to generalize this mechanism
 to pass a full list of type indexes and desired types, but I haven't
 run into a case like that yet.


https://reviews.llvm.org/D83884

Files:
  llvm/docs/GlobalISel/Legalizer.rst
  llvm/include/llvm/CodeGen/GlobalISel/LegalizerInfo.h
  llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp

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