[Pipeline] Remove early InstCombine in ThinLTO post link sample profile pipeline

[aeubanks]

Summary

With opaque pointers, all function pointer types are the same, meaning there should be no bitcasts.

Internal benchmarks with SampleFDO look neutral.

This was added in D36333.

[tejohnson]

lgtm, but please wait to see if @davidxl wants to re-anchor any of the comments there, specifically the FIXME.

llvm/lib/Passes/PassBuilderPipelines.cpp

976

@davidxl is this comment still needed?

[davidxl]

llvm/lib/Passes/PassBuilderPipelines.cpp

976

this comment is obsolete as bitcast is no longer there (to block exposing direct calls).

llvm/lib/Passes/PassBuilderPipelines.cpp

PassBuilder::buildModuleSimplificationPipeline(OptimizationLevel Level,
   // Compare/branch metadata may alter the behavior of passes like SimplifyCFG.
   EarlyFPM.addPass(LowerExpectIntrinsicPass());
   EarlyFPM.addPass(SimplifyCFGPass());
   EarlyFPM.addPass(SROAPass(SROAOptions::ModifyCFG));
   EarlyFPM.addPass(EarlyCSEPass());
   if (Level == OptimizationLevel::O3)
     EarlyFPM.addPass(CallSiteSplittingPass());
 
-  // In SamplePGO ThinLTO backend, we need instcombine before profile annotation
-  // to convert bitcast to direct calls so that they can be inlined during the
-  // profile annotation prepration step.
-  // More details about SamplePGO design can be found in:
-  // https://research.google.com/pubs/pub45290.html
-  // FIXME: revisit how SampleProfileLoad/Inliner/ICP is structured.
-  if (LoadSampleProfile)
-    EarlyFPM.addPass(InstCombinePass());
   MPM.addPass(createModuleToFunctionPassAdaptor(std::move(EarlyFPM),
                                                 PTO.EagerlyInvalidateAnalyses));
 
   if (LoadSampleProfile) {
     // Annotate sample profile right after early FPM to ensure freshness of
     // the debug info.
     MPM.addPass(SampleProfileLoaderPass(PGOOpt->ProfileFile,
                                         PGOOpt->ProfileRemappingFile, Phase));

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

 ; USE_POST_LINK: Running pass: PGOIndirectCallPromotion
 ; USE_POST_LINK: Running pass: PGOMemOPSizeOpt
 ; SAMPLE_USE_O: Running pass: AddDiscriminatorsPass
 ; SAMPLE_USE_PRE_LINK: Running pass: AddDiscriminatorsPass
 ; SAMPLE_USE: Running pass: LowerExpectIntrinsicPass
 ; SAMPLE_USE: Running pass: SimplifyCFGPass
 ; SAMPLE_USE: Running pass: SROAPass
 ; SAMPLE_USE: Running pass: EarlyCSEPass
-; SAMPLE_USE_POST_LINK: Running pass: InstCombinePass
 ; SAMPLE_USE: Running pass: SampleProfileLoaderPass
 ; SAMPLE_USE_O: Running pass: PGOIndirectCallPromotion
 ; SAMPLE_USE_POST_LINK-NOT: Running pass: GlobalOptPass
 ; SAMPLE_USE_POST_LINK: Running pass: PGOIndirectCallPromotion
 ; SAMPLE_USE_PRE_LINK-NOT: Running pass: PGOIndirectCallPromotion
 ; SAMPLE_GEN: Running pass: AddDiscriminatorsPass
 ; SPLIT: Running pass: HotColdSplittingPass
 
 define void @foo() {
   ret void
 }

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

 ; CHECK-O-NEXT: Running pass: SimplifyCFGPass
 ; CHECK-O-NEXT: Running analysis: TargetIRAnalysis
 ; CHECK-O-NEXT: Running analysis: AssumptionAnalysis
 ; CHECK-O-NEXT: Running pass: SROAPass
 ; CHECK-O-NEXT: Running analysis: DominatorTreeAnalysis
 ; CHECK-O-NEXT: Running pass: EarlyCSEPass
 ; CHECK-O-NEXT: Running analysis: TargetLibraryAnalysis
 ; CHECK-O3-NEXT: Running pass: CallSiteSplittingPass
-; CHECK-O-NEXT: Running pass: InstCombinePass on foo
-; CHECK-O-NEXT: Running analysis: OptimizationRemarkEmitterAnalysis on foo
-; CHECK-O-NEXT: Running analysis: AAManager on foo
-; CHECK-O-NEXT: Running analysis: BasicAA
-; CHECK-O-NEXT: Running analysis: ScopedNoAliasAA
-; CHECK-O-NEXT: Running analysis: TypeBasedAA
-; CHECK-O-NEXT: Running analysis: OuterAnalysisManagerProxy
 ; CHECK-O-NEXT: Running pass: SampleProfileLoaderPass
 ; CHECK-O-NEXT: Running analysis: ProfileSummaryAnalysis
 ; CHECK-O-NEXT: Running analysis: CallGraphAnalysis
 ; CHECK-O-NEXT: Running pass: RequireAnalysisPass<{{.*}}ProfileSummaryAnalysis
 ; CHECK-O-NEXT: Running pass: PGOIndirectCallPromotion
+; CHECK-O-NEXT: Running analysis: OptimizationRemarkEmitterAnalysis
 ; CHECK-O-NEXT: Running pass: OpenMPOptPass
 ; CHECK-O-NEXT: Running pass: LowerTypeTestsPass
 ; CHECK-O-NEXT: Running pass: IPSCCPPass
 ; CHECK-O123-NEXT: Running analysis: LoopAnalysis on foo
 ; CHECK-O-NEXT: Running pass: CalledValuePropagationPass
 ; CHECK-O-NEXT: Running pass: GlobalOptPass
 ; CHECK-O-NEXT: Running pass: PromotePass
 ; CHECK-O-NEXT: Running pass: InstCombinePass
+; CHECK-O-NEXT: Running analysis: AAManager on foo
+; CHECK-O-NEXT: Running analysis: BasicAA
+; CHECK-O-NEXT: Running analysis: ScopedNoAliasAA
+; CHECK-O-NEXT: Running analysis: TypeBasedAA
+; CHECK-O-NEXT: Running analysis: OuterAnalysisManagerProxy
 ; CHECK-O-NEXT: Running analysis: BlockFrequencyAnalysis on foo
 ; These next two can appear in any order since they are accessed as parameters
 ; on the same call to BlockFrequencyInfo::calculate.
 ; CHECK-OSZ-DAG: Running analysis: LoopAnalysis on foo
 ; CHECK-OSZ-DAG: Running analysis: BranchProbabilityAnalysis on foo
 ; CHECK-O123-NEXT: Running analysis: BranchProbabilityAnalysis on foo
 ; CHECK-O-NEXT: Running analysis: PostDominatorTreeAnalysis on foo
 ; CHECK-O-NEXT: Running pass: SimplifyCFGPass on foo

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

 ; CHECK-O-NEXT: Running pass: SimplifyCFGPass
 ; CHECK-O-NEXT: Running analysis: TargetIRAnalysis
 ; CHECK-O-NEXT: Running analysis: AssumptionAnalysis
 ; CHECK-O-NEXT: Running pass: SROAPass
 ; CHECK-O-NEXT: Running analysis: DominatorTreeAnalysis
 ; CHECK-O-NEXT: Running pass: EarlyCSEPass
 ; CHECK-O-NEXT: Running analysis: TargetLibraryAnalysis
 ; CHECK-O3-NEXT: Running pass: CallSiteSplittingPass
-; CHECK-O-NEXT: Running pass: InstCombinePass on foo
-; CHECK-O-NEXT: Running analysis: OptimizationRemarkEmitterAnalysis on foo
-; CHECK-O-NEXT: Running analysis: AAManager on foo
-; CHECK-O-NEXT: Running analysis: BasicAA
-; CHECK-O-NEXT: Running analysis: ScopedNoAliasAA
-; CHECK-O-NEXT: Running analysis: TypeBasedAA
-; CHECK-O-NEXT: Running analysis: OuterAnalysisManagerProxy
 ; CHECK-O-NEXT: Running pass: SampleProfileLoaderPass
 ; CHECK-O-NEXT: Running analysis: ProfileSummaryAnalysis
 ; CHECK-O-NEXT: Running analysis: CallGraphAnalysis
 ; CHECK-O-NEXT: Running pass: RequireAnalysisPass<{{.*}}ProfileSummaryAnalysis
 ; CHECK-O-NEXT: Running pass: OpenMPOptPass
 ; CHECK-O-NEXT: Running pass: IPSCCPPass
 ; CHECK-O-NEXT: Running pass: CalledValuePropagationPass
 ; CHECK-O-NEXT: Running pass: GlobalOptPass
 ; CHECK-O-NEXT: Running pass: PromotePass
 ; CHECK-O-NEXT: Running pass: InstCombinePass
+; CHECK-O-NEXT: Running analysis: OptimizationRemarkEmitterAnalysis on foo
+; CHECK-O-NEXT: Running analysis: AAManager on foo
+; CHECK-O-NEXT: Running analysis: BasicAA
+; CHECK-O-NEXT: Running analysis: ScopedNoAliasAA
+; CHECK-O-NEXT: Running analysis: TypeBasedAA
+; CHECK-O-NEXT: Running analysis: OuterAnalysisManagerProxy
 ; CHECK-O-NEXT: Running analysis: BlockFrequencyAnalysis on foo
 ; These next two can appear in any order since they are accessed as parameters
 ; on the same call to BlockFrequencyInfo::calculate.
 ; CHECK-O-DAG: Running analysis: LoopAnalysis on foo
 ; CHECK-O-DAG: Running analysis: BranchProbabilityAnalysis on foo
 ; CHECK-O-NEXT: Running analysis: PostDominatorTreeAnalysis on foo
 ; CHECK-O-NEXT: Running pass: SimplifyCFGPass on foo
 ; CHECK-O-NEXT: Running pass: ModuleInlinerWrapperPass