[all-commits] [llvm/llvm-project] a15dab: [SCEV] Introduce SCEVUse, use it instead of const ...

[Florian Hahn via All-commits]

  Branch: refs/heads/users/fhahn/scevuse
  Home:   https://github.com/llvm/llvm-project
  Commit: a15daba1c6cec22d39eed44c969ebfa973ad5c58
      https://github.com/llvm/llvm-project/commit/a15daba1c6cec22d39eed44c969ebfa973ad5c58
  Author: Florian Hahn <flo at fhahn.com>
  Date:   2024-11-25 (Mon, 25 Nov 2024)

  Changed paths:
    M llvm/include/llvm/Analysis/ScalarEvolution.h
    M llvm/include/llvm/Analysis/ScalarEvolutionExpressions.h
    M llvm/lib/Analysis/DependenceAnalysis.cpp
    M llvm/lib/Analysis/IVDescriptors.cpp
    M llvm/lib/Analysis/LoopCacheAnalysis.cpp
    M llvm/lib/Analysis/ScalarEvolution.cpp
    M llvm/lib/Target/PowerPC/PPCLoopInstrFormPrep.cpp
    M llvm/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
    M llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
    M llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
    M llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
    M llvm/test/Transforms/IndVarSimplify/turn-to-invariant.ll
    M llvm/unittests/Analysis/ScalarEvolutionTest.cpp

  Log Message:
  -----------
  [SCEV] Introduce SCEVUse, use it instead of const SCEV * (NFCI) (WIP).

This patch introduces SCEVUse, which is a tagged pointer containing the
used const SCEV *, plus extra bits to store NUW/NSW flags that are only
valid at the specific use.

This was suggested by @nikic as an alternative
to https://github.com/llvm/llvm-project/pull/90742.

This patch just updates most SCEV infrastructure to operate on SCEVUse
instead of const SCEV *. It does not introduce any code that makes use
of the use-specific flags yet which I'll share as follow-ups.

Note that this should be NFC, but currently there's at least one case
where it is not (turn-to-invariant.ll), which I'll investigate once we
agree on the overall direction.

This PR at the moment also contains a commit that updates various SCEV
clients to use `const SCEV *` instead of `const auto *`, to prepare for
this patch. This reduces the number of changes needed, as SCEVUse will
automatically convert to `const SCEV *`. This is a safe default, as it
just drops the use-specific flags for the expression (it will not drop
any use-specific flags for any of its operands though).

This probably
SCEVUse could probably also be used to address mis-compiles due to
equivalent AddRecs modulo flags result in an AddRec with incorrect flags
for some uses of some phis, e.g. the one
https://github.com/llvm/llvm-project/pull/80430 attempted to fix

Compile-time impact:
stage1-O3: +0.06%
stage1-ReleaseThinLTO: +0.07%
stage1-ReleaseLTO-g: +0.07%
stage2-O3: +0.11%

https://llvm-compile-time-tracker.com/compare.php?from=ce055843e2be9643bd58764783a7bb69f6db8c9a&to=8c7f4e9e154ebc4862c4e2716cedc3c688352d7c&stat=instructions:u

!fixup use raw pointer (const SCEV * + lower bits) for AddPointer.

!fix formatting

!fixup fix build failures after rebase, address comments

!fixup isCanonical/getCanonical

Simp



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