[all-commits] [llvm/llvm-project] b28eeb: [RDF] Fix cover check when linking refs to defs (#...

[Yashas Andaluri via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: b28eebf9264a6b6843b15d4e17be70604f3e4ad8
      https://github.com/llvm/llvm-project/commit/b28eebf9264a6b6843b15d4e17be70604f3e4ad8
  Author: Yashas Andaluri <quic_yandalur at quicinc.com>
  Date:   2024-11-19 (Tue, 19 Nov 2024)

  Changed paths:
    M llvm/lib/CodeGen/RDFGraph.cpp
    A llvm/test/CodeGen/Hexagon/rdf-dce-double-cover.mir

  Log Message:
  -----------
  [RDF] Fix cover check when linking refs to defs (#113888)

During RDF graph construction, linkRefUp method links a register ref to
its upward reaching defs until all RegUnits of the ref have been covered
by defs.
However, when a sub-register def covers some, but not all, of the
RegUnits of a previous super-register def, a super-register ref is not
linked to the super-register def.
This can result in certain super register defs being dead code
eliminated.

This patch fixes the cover check for a register ref. A def must be
skipped only when all RegUnits of that def have already been covered by
a previously seen def.



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