[all-commits] [llvm/llvm-project] 377b0e: [TableGen] Don't elide bitconverts in PatFrag frag...

[Simon Tatham via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 377b0e2b06f90c4edbd320cf9d833af5979f8f5d
      https://github.com/llvm/llvm-project/commit/377b0e2b06f90c4edbd320cf9d833af5979f8f5d
  Author: Simon Tatham <simon.tatham at arm.com>
  Date:   2020-02-17 (Mon, 17 Feb 2020)

  Changed paths:
    A llvm/test/TableGen/simplify-patfrag.td
    M llvm/utils/TableGen/CodeGenDAGPatterns.cpp

  Log Message:
  -----------
  [TableGen] Don't elide bitconverts in PatFrag fragments.

Summary:
In the DAG pattern backend, `SimplifyTree` simplifies a pattern by
removing bitconverts between two identical types. But that function is
also run on the fragments list in instances of `PatFrags`, in which
the types haven't been specified yet. So the input and output of the
bitconvert always evaluate to the empty set of types, which makes them
compare equal. So the test always passes, and bitconverts are
unconditionally removed from the PatFrag RHS.

Fixed by spotting the empty type set and using it to inhibit the
optimization.

Reviewers: nhaehnle, hfinkel

Reviewed By: nhaehnle

Subscribers: llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D74627