Unverified Commit a8d74517 authored by Roman Lebedev's avatar Roman Lebedev
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[PassManager] Run Induction Variable Simplification pass *after* Recognize... 

[PassManager] Run Induction Variable Simplification pass *after* Recognize loop idioms pass, not before

Currently, `-indvars` runs first, and then immediately after `-loop-idiom` does.
I'm not really sure if `-loop-idiom` requires `-indvars` to run beforehand,
but i'm *very* sure that `-indvars` requires `-loop-idiom` to run afterwards,
as it can be seen in the phase-ordering test.

LoopIdiom runs on two types of loops: countable ones, and uncountable ones.
For uncountable ones, IndVars obviously didn't make any change to them,
since they are uncountable, so for them the order should be irrelevant.
For countable ones, well, they should have been countable before IndVars
for IndVars to make any change to them, and since SCEV is used on them,
it shouldn't matter if IndVars have already canonicalized them.
So i don't really see why we'd want the current ordering.

Should this cause issues, it will give us a reproducer test case
that shows flaws in this logic, and we then could adjust accordingly.

While this is quite likely beneficial in-the-wild already,
it's a required part for the full motivational pattern
behind `left-shift-until-bittest` loop idiom (D91038).

Reviewed By: dmgreen

Differential Revision: https://reviews.llvm.org/D91800
parent 1933c9d4

llvm/lib/Passes/PassBuilder.cpp

+3 −3
Original line number Diff line number Diff line
@@ -521,8 +521,8 @@ PassBuilder::buildO1FunctionSimplificationPipeline(OptimizationLevel Level, 


  if (EnableLoopFlatten)

    FPM.addPass(LoopFlattenPass());

  LPM2.addPass(IndVarSimplifyPass());

  LPM2.addPass(LoopIdiomRecognizePass());

  LPM2.addPass(IndVarSimplifyPass());



  for (auto &C : LateLoopOptimizationsEPCallbacks)

    C(LPM2, Level);
@@ -682,8 +682,8 @@ PassBuilder::buildFunctionSimplificationPipeline(OptimizationLevel Level, 
  // TODO: Investigate promotion cap for O1.

  LPM1.addPass(LICMPass(PTO.LicmMssaOptCap, PTO.LicmMssaNoAccForPromotionCap));

  LPM1.addPass(SimpleLoopUnswitchPass());

  LPM2.addPass(IndVarSimplifyPass());

  LPM2.addPass(LoopIdiomRecognizePass());

  LPM2.addPass(IndVarSimplifyPass());



  for (auto &C : LateLoopOptimizationsEPCallbacks)

    C(LPM2, Level);
@@ -712,7 +712,7 @@ PassBuilder::buildFunctionSimplificationPipeline(OptimizationLevel Level, 
      DebugLogging));

  FPM.addPass(SimplifyCFGPass());

  FPM.addPass(InstCombinePass());

  // The loop passes in LPM2 (IndVarSimplifyPass, LoopIdiomRecognizePass,

  // The loop passes in LPM2 (LoopIdiomRecognizePass, IndVarSimplifyPass,

  // LoopDeletionPass and LoopFullUnrollPass) do not preserve MemorySSA.

  // *All* loop passes must preserve it, in order to be able to use it.

  FPM.addPass(createFunctionToLoopPassAdaptor(

llvm/lib/Transforms/IPO/PassManagerBuilder.cpp

+1 −1
Original line number Diff line number Diff line
@@ -445,8 +445,8 @@ void PassManagerBuilder::addFunctionSimplificationPasses( 
    MPM.add(createLoopFlattenPass()); // Flatten loops

    MPM.add(createLoopSimplifyCFGPass());

  }

  MPM.add(createIndVarSimplifyPass());        // Canonicalize indvars

  MPM.add(createLoopIdiomPass());             // Recognize idioms like memset.

  MPM.add(createIndVarSimplifyPass());        // Canonicalize indvars

  addExtensionsToPM(EP_LateLoopOptimizations, MPM);

  MPM.add(createLoopDeletionPass());          // Delete dead loops

llvm/test/CodeGen/AMDGPU/opt-pipeline.ll

+1 −1
Original line number Diff line number Diff line
@@ -163,8 +163,8 @@ 
; GCN-O1-NEXT:       Loop-Closed SSA Form Pass

; GCN-O1-NEXT:       Scalar Evolution Analysis

; GCN-O1-NEXT:       Loop Pass Manager

; GCN-O1-NEXT:         Induction Variable Simplification

; GCN-O1-NEXT:         Recognize loop idioms

; GCN-O1-NEXT:         Induction Variable Simplification

; GCN-O1-NEXT:         Delete dead loops

; GCN-O1-NEXT:         Unroll loops

; GCN-O1-NEXT:       SROA

llvm/test/Other/new-pm-defaults.ll

+1 −1
Original line number Diff line number Diff line
@@ -163,8 +163,8 @@ 
; CHECK-O-NEXT: Running pass: LCSSAPass

; CHECK-O-NEXT: Finished llvm::Function pass manager run.

; CHECK-O-NEXT: Starting Loop pass manager run.

; CHECK-O-NEXT: Running pass: IndVarSimplifyPass

; CHECK-O-NEXT: Running pass: LoopIdiomRecognizePass

; CHECK-O-NEXT: Running pass: IndVarSimplifyPass

; CHECK-EP-LOOP-LATE-NEXT: Running pass: NoOpLoopPass

; CHECK-O-NEXT: Running pass: LoopDeletionPass

; CHECK-O-NEXT: Running pass: LoopFullUnrollPass

llvm/test/Other/new-pm-thinlto-defaults.ll

+1 −1
Original line number Diff line number Diff line
@@ -147,8 +147,8 @@ 
; CHECK-O-NEXT: Running pass: LCSSAPass

; CHECK-O-NEXT: Finished llvm::Function pass manager run

; CHECK-O-NEXT: Starting Loop pass manager run.

; CHECK-O-NEXT: Running pass: IndVarSimplifyPass

; CHECK-O-NEXT: Running pass: LoopIdiomRecognizePass

; CHECK-O-NEXT: Running pass: IndVarSimplifyPass

; CHECK-O-NEXT: Running pass: LoopDeletionPass

; CHECK-O-NEXT: Running pass: LoopFullUnrollPass

; CHECK-O-NEXT: Finished Loop pass manager run.