[all-commits] [llvm/llvm-project] 0411e3: [SCEV] Speed up forgetLoop by avoiding def-use wal...

[Mingjie Xu via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 0411e39a35866c125750810e59a15e00c9484fc9
      https://github.com/llvm/llvm-project/commit/0411e39a35866c125750810e59a15e00c9484fc9
  Author: Mingjie Xu <xumingjie.enna1 at bytedance.com>
  Date:   2026-06-10 (Wed, 10 Jun 2026)

  Changed paths:
    M llvm/lib/Analysis/ScalarEvolution.cpp
    M llvm/unittests/Analysis/ScalarEvolutionTest.cpp

  Log Message:
  -----------
  [SCEV] Speed up forgetLoop by avoiding def-use walk for loop-header PHIs (#201572)

Every cached SCEV varies with Loop `L` transitively contains an
`AddRec`, and every `AddRec` for the loop is recorded in `LoopUsers[L]`.
`forgetMemoizedResults` already closes this set transitively through
`SCEVUsers` and `ExprValueMap`.
Therefore `forgetLoop` does not need to walk the def-use chain starting
from header PHIs, it only needs to initialize `ToForget` with
`LoopUsers[L]` and explicitly remove each header PHI's entries from
`ValueExprMap` and `ConstantEvolutionLoopExitValue`, push its cached
SCEVs into `ToForget`.
As a side effect, cached SCEVs that reside in the loop body but do not
depend on any `AddRec` for the loop (e.g. a `SCEVUnknown` for an icmp)
are no longer invalidated.



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