Turn on flag to not re-run simplification pipeline.

[asbirlea]

Summary

This patch turns on the flag -enable-no-rerun-simplification-pipeline, which means the simplification pipeline will not be rerun on unchanged functions in the CGSCCPass Manager.

Compile time improvement:
https://llvm-compile-time-tracker.com/compare.php?from=17457be1c393ff691cca032b04ea1698fedf0301&to=882301ebb893c8ef9f09fe1ea871f7995426fa07&stat=instructions

No meaningful run time regressions observed in the llvm test suite and
in additional internal workloads at this time.

The example test in test/Other/no-rerun-function-simplification-pipeline.ll is a good means to understand the effect of this change:

define void @f1(void()* %p) alwaysinline {
  call void %p()
  ret void
}

define void @f2() #0 {
  call void @f1(void()* @f2)
  call void @f3()
  ret void
}

define void @f3() #0 {
  call void @f2()
  ret void
}

There are two SCCs formed by the ModuleToPostOrderCGSCCAdaptor: (f1) and (f2, f3).

The pass manager runs on the first SCC, leading to running the simplification pipeline (function and loop passes) on f1. With the flag on, after this, the output will have Running analysis: ShouldNotRunFunctionPassesAnalysis on f1.

Next, the pass manager runs on the second SCC: (f2, f3). Since f1() was inlined, f2() now calls itself, and also calls f3(), while f3() only calls f2().
So the pass manager for the SCC first runs the Inliner on (f2, f3), then the simplification pipeline on f2.
With the flag on, the output will have Running analysis: ShouldNotRunFunctionPassesAnalysis on f2; unless the inliner makes a change, this analysis remains preserved which means there's no reason to rerun the simplification pipeline. With the flag off, there is a second run of the simplification pipeline run on f2.

Next, the same flow occurs for f3. The simplification pipeline is run on f3 a single time with the flag on, along with ShouldNotRunFunctionPassesAnalysis on f3, and twice with the flag off.
The reruns occur only on f2 and f3 due to the additional ref edges.

[aeubanks]

lg on my side although I'd like other people to approve after getting more metrics

I'd give a more concrete example in the summary, e.g. the example in https://reviews.llvm.org/D113947

[fhahn]

Compile time improvement:
https://llvm-compile-time-tracker.com/compare.php?from=17457be1c393ff691cca032b04ea1698fedf0301&to=882301ebb893c8ef9f09fe1ea871f7995426fa07&stat=instructions

No meaningful run time regressions observed in the llvm test suite and
in additional internal workloads at this time.

Do you have any insight in what kind of binary changes to expect and what the potential sources are?

[aeubanks]

regressions would come up in the form of functions where running the function simplification pipeline more than once on it results in more simplification, i.e. phase ordering issues, and the function happened to have the function simplification get run on it more than once due to how the CGSCC pass manager visits SCCs

[nikic]

Yay!

[asbirlea]

For additional context, this is a follow up of D98103. At the time we were seeing large run time regressions and the goal was to understand how to modify the pipeline to resolve them.
Today, on the same workloads, the regressions are resolved. It’s not clear what specific change led to this, and if there are other workloads that will regress due to phase ordering issues and possibly needing additional passes to be added.
The flag flip should answer this question and I will iterate if regressions are reported.

The clear benefit is the reduction in compile time due to not rerunning passes on functions where no changes occurred. I included the explanation based on the no-rerun-function-simplification-pipeline.ll test in the description.

[asbirlea]

https://reviews.llvm.org/rG846d10f16a573401191e406d3752b6f60c7d6459

[fhahn]

Sounds good, thanks! We should have our internal performance results by EOD/tomorrow. If there are any regressions I'll let you know.

llvm/lib/Passes/PassBuilderPipelines.cpp

static cl::opt<bool> EnableO3NonTrivialUnswitching(
     "enable-npm-O3-nontrivial-unswitch", cl::init(true), cl::Hidden,
     cl::desc("Enable non-trivial loop unswitching for -O3"));
 
 static cl::opt<bool> EnableEagerlyInvalidateAnalyses(
     "eagerly-invalidate-analyses", cl::init(true), cl::Hidden,
     cl::desc("Eagerly invalidate more analyses in default pipelines"));
 
 static cl::opt<bool> EnableNoRerunSimplificationPipeline(
-    "enable-no-rerun-simplification-pipeline", cl::init(false), cl::Hidden,
+    "enable-no-rerun-simplification-pipeline", cl::init(true), cl::Hidden,
     cl::desc(
         "Prevent running the simplification pipeline on a function more "
         "than once in the case that SCC mutations cause a function to be "
         "visited multiple times as long as the function has not been changed"));
 
 static cl::opt<bool> EnableMergeFunctions(
     "enable-merge-functions", cl::init(false), cl::Hidden,
     cl::desc("Enable function merging as part of the optimization pipeline"));

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

 ; CHECK-O23SZ-NEXT: Running pass: LoopSimplifyPass
 ; CHECK-O23SZ-NEXT: Running pass: LCSSAPass
 ; CHECK-O23SZ-NEXT: Running pass: LICMPass
 ; CHECK-O23SZ-NEXT: Running pass: CoroElidePass
 ; CHECK-EP-SCALAR-LATE-NEXT: Running pass: NoOpFunctionPass
 ; CHECK-O-NEXT: Running pass: SimplifyCFGPass
 ; CHECK-O-NEXT: Running pass: InstCombinePass
 ; CHECK-EP-PEEPHOLE-NEXT: Running pass: NoOpFunctionPass
+; CHECK-O-NEXT: Running analysis: ShouldNotRunFunctionPassesAnalysis
 ; CHECK-O-NEXT: Running pass: CoroSplitPass
+; CHECK-O-NEXT: Running pass: InvalidateAnalysisPass<{{.*}}ShouldNotRunFunctionPassesAnalysis
+; CHECK-O-NEXT: Invalidating analysis: ShouldNotRunFunctionPassesAnalysis
 ; CHECK-O-NEXT: Invalidating analysis: InlineAdvisorAnalysis
 ; CHECK-O-NEXT: Running pass: CoroCleanupPass
 ; CHECK-O-NEXT: Running pass: GlobalOptPass
 ; CHECK-O-NEXT: Running pass: GlobalDCEPass
 ; CHECK-DEFAULT-NEXT: Running pass: EliminateAvailableExternallyPass
 ; CHECK-LTO-NOT: Running pass: EliminateAvailableExternallyPass
 ; CHECK-O-NEXT: Running pass: ReversePostOrderFunctionAttrsPass
 ; CHECK-O-NEXT: Running pass: RecomputeGlobalsAAPass

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

 ; CHECK-O23SZ-NEXT: Running pass: MemCpyOptPass
 ; CHECK-O23SZ-NEXT: Running pass: DSEPass
 ; CHECK-O23SZ-NEXT: Running pass: LoopSimplifyPass
 ; CHECK-O23SZ-NEXT: Running pass: LCSSAPass
 ; CHECK-O23SZ-NEXT: Running pass: LICMPass on Loop at depth 1 containing: %loop
 ; CHECK-O23SZ-NEXT: Running pass: CoroElidePass
 ; CHECK-O-NEXT: Running pass: SimplifyCFGPass
 ; CHECK-O-NEXT: Running pass: InstCombinePass
+; CHECK-O-NEXT: Running analysis: ShouldNotRunFunctionPassesAnalysis
 ; CHECK-O-NEXT: Running pass: CoroSplitPass
+; CHECK-O-NEXT: Running pass: InvalidateAnalysisPass<{{.*}}ShouldNotRunFunctionPassesAnalysis
+; CHECK-O-NEXT: Invalidating analysis: ShouldNotRunFunctionPassesAnalysis
 ; CHECK-O-NEXT: Invalidating analysis: InlineAdvisorAnalysis
 ; CHECK-O-NEXT: Running pass: CoroCleanupPass
 ; CHECK-PRELINK-O-NEXT: Running pass: GlobalOptPass
 ; CHECK-POSTLINK-O-NEXT: Running pass: GlobalOptPass
 ; CHECK-POSTLINK-O-NEXT: Running pass: GlobalDCEPass
 ; CHECK-POSTLINK-O-NEXT: Running pass: EliminateAvailableExternallyPass
 ; CHECK-POSTLINK-O-NEXT: Running pass: ReversePostOrderFunctionAttrsPass
 ; CHECK-POSTLINK-O-NEXT: Running pass: RecomputeGlobalsAAPass

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

 ; CHECK-O23SZ-NEXT: Running pass: MemCpyOptPass
 ; CHECK-O23SZ-NEXT: Running pass: DSEPass
 ; CHECK-O23SZ-NEXT: Running pass: LoopSimplifyPass
 ; CHECK-O23SZ-NEXT: Running pass: LCSSAPass
 ; CHECK-O23SZ-NEXT: Running pass: LICMPass
 ; CHECK-O23SZ-NEXT: Running pass: CoroElidePass
 ; CHECK-O-NEXT: Running pass: SimplifyCFGPass
 ; CHECK-O-NEXT: Running pass: InstCombinePass
+; CHECK-O-NEXT: Running analysis: ShouldNotRunFunctionPassesAnalysis
 ; CHECK-O-NEXT: Running pass: CoroSplitPass
+; CHECK-O-NEXT: Running pass: InvalidateAnalysisPass<{{.*}}ShouldNotRunFunctionPassesAnalysis
+; CHECK-O-NEXT: Invalidating analysis: ShouldNotRunFunctionPassesAnalysis
 ; CHECK-O-NEXT: Invalidating analysis: InlineAdvisorAnalysis
 ; CHECK-O-NEXT: Running pass: CoroCleanupPass
 ; CHECK-O-NEXT: Running pass: GlobalOptPass
 ; CHECK-O-NEXT: Running pass: GlobalDCEPass
 ; CHECK-O-NEXT: Running pass: EliminateAvailableExternallyPass
 ; CHECK-O-NEXT: Running pass: ReversePostOrderFunctionAttrsPass
 ; CHECK-O-NEXT: Running pass: RecomputeGlobalsAAPass
 ; CHECK-O-NEXT: Running pass: Float2IntPass

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

 ; CHECK-O23SZ-NEXT: Running pass: LCSSAPass
 ; CHECK-O23SZ-NEXT: Running pass: LICMPass
 ; CHECK-O23SZ-NEXT: Running pass: CoroElidePass
 ; CHECK-O-NEXT: Running pass: SimplifyCFGPass
 ; CHECK-O-NEXT: Running pass: InstCombinePass
 ; CHECK-O3-NEXT: Running pass: ControlHeightReductionPass on foo
 ; CHECK-O3-NEXT: Running analysis: RegionInfoAnalysis on foo
 ; CHECK-O3-NEXT: Running analysis: DominanceFrontierAnalysis on foo
+; CHECK-O-NEXT: Running analysis: ShouldNotRunFunctionPassesAnalysis
 ; CHECK-O-NEXT: Running pass: CoroSplitPass
+; CHECK-O-NEXT: Running pass: InvalidateAnalysisPass<{{.*}}ShouldNotRunFunctionPassesAnalysis
+; CHECK-O-NEXT: Invalidating analysis: ShouldNotRunFunctionPassesAnalysis
 ; CHECK-O-NEXT: Invalidating analysis: InlineAdvisorAnalysis
 ; CHECK-O-NEXT: Running pass: CoroCleanupPass
 ; CHECK-O-NEXT: Running pass: GlobalOptPass
 ; CHECK-O-NEXT: Running pass: GlobalDCEPass
 ; CHECK-O-NEXT: Running pass: EliminateAvailableExternallyPass
 ; CHECK-O-NEXT: Running pass: ReversePostOrderFunctionAttrsPass
 ; CHECK-O-NEXT: Running pass: RecomputeGlobalsAAPass
 ; CHECK-O-NEXT: Running pass: Float2IntPass

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

 ; CHECK-O23SZ-NEXT: Running pass: LCSSAPass
 ; CHECK-O23SZ-NEXT: Running pass: LICMPass
 ; CHECK-O23SZ-NEXT: Running pass: CoroElidePass
 ; CHECK-O-NEXT: Running pass: SimplifyCFGPass
 ; CHECK-O-NEXT: Running pass: InstCombinePass
 ; CHECK-O3-NEXT: Running pass: ControlHeightReductionPass on foo
 ; CHECK-O3-NEXT: Running analysis: RegionInfoAnalysis on foo
 ; CHECK-O3-NEXT: Running analysis: DominanceFrontierAnalysis on foo
+; CHECK-O-NEXT: Running analysis: ShouldNotRunFunctionPassesAnalysis
 ; CHECK-O-NEXT: Running pass: CoroSplitPass
+; CHECK-O-NEXT: Running pass: InvalidateAnalysisPass<{{.*}}ShouldNotRunFunctionPassesAnalysis
+; CHECK-O-NEXT: Invalidating analysis: ShouldNotRunFunctionPassesAnalysis
 ; CHECK-O-NEXT: Invalidating analysis: InlineAdvisorAnalysis
 ; CHECK-O-NEXT: Running pass: CoroCleanupPass
 ; CHECK-O-NEXT: Running pass: GlobalOptPass
 ; CHECK-O-NEXT: Running analysis: TargetLibraryAnalysis on bar
 ; CHECK-EXT: Running pass: {{.*}}::Bye
 ; CHECK-O-NEXT: Running pass: AnnotationRemarksPass on foo
 ; CHECK-O-NEXT: Running pass: CanonicalizeAliasesPass
 ; CHECK-O-NEXT: Running pass: NameAnonGlobalPass

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

 ; CHECK-O23SZ-NEXT: Running pass: LCSSAPass
 ; CHECK-O23SZ-NEXT: Running pass: LICMPass
 ; CHECK-O23SZ-NEXT: Running pass: CoroElidePass
 ; CHECK-O-NEXT: Running pass: SimplifyCFGPass
 ; CHECK-O-NEXT: Running pass: InstCombinePass
 ; CHECK-O3-NEXT: Running pass: ControlHeightReductionPass on foo
 ; CHECK-O3-NEXT: Running analysis: RegionInfoAnalysis on foo
 ; CHECK-O3-NEXT: Running analysis: DominanceFrontierAnalysis on foo
+; CHECK-O-NEXT: Running analysis: ShouldNotRunFunctionPassesAnalysis
 ; CHECK-O-NEXT: Running pass: CoroSplitPass
+; CHECK-O-NEXT: Running pass: InvalidateAnalysisPass<{{.*}}ShouldNotRunFunctionPassesAnalysis
+; CHECK-O-NEXT: Invalidating analysis: ShouldNotRunFunctionPassesAnalysis
 ; CHECK-O-NEXT: Invalidating analysis: InlineAdvisorAnalysis
 ; CHECK-O-NEXT: Running pass: CoroCleanupPass
 ; CHECK-O-NEXT: Running pass: GlobalOptPass
 ; CHECK-O-NEXT: Running pass: AnnotationRemarksPass on foo
 ; CHECK-O-NEXT: Running pass: CanonicalizeAliasesPass
 ; CHECK-O-NEXT: Running pass: NameAnonGlobalPass
 ; CHECK-O-NEXT: Running pass: PrintModulePass
 

llvm/test/Other/no-rerun-function-simplification-pipeline.ll

-; RUN: opt < %s -passes='default<O1>' -disable-output -debug-pass-manager=verbose 2>&1 | FileCheck %s --check-prefixes=CHECK,NORMAL
-; RUN: opt < %s -passes='default<O2>' -disable-output -debug-pass-manager=verbose 2>&1 | FileCheck %s --check-prefixes=CHECK,NORMAL
+; RUN: opt < %s -passes='default<O1>' -disable-output -debug-pass-manager=verbose -enable-no-rerun-simplification-pipeline=0 2>&1 | FileCheck %s --check-prefixes=CHECK,RERUNSP
+; RUN: opt < %s -passes='default<O2>' -disable-output -debug-pass-manager=verbose -enable-no-rerun-simplification-pipeline=0 2>&1 | FileCheck %s --check-prefixes=CHECK,RERUNSP
 ; RUN: opt < %s -passes='default<O1>' -disable-output -debug-pass-manager=verbose -enable-no-rerun-simplification-pipeline=1 2>&1 | FileCheck %s --check-prefixes=CHECK,NORERUN
 ; RUN: opt < %s -passes='default<O2>' -disable-output -debug-pass-manager=verbose -enable-no-rerun-simplification-pipeline=1 2>&1 | FileCheck %s --check-prefixes=CHECK,NORERUN
 
 ; BDCE only runs once in the function simplification pipeline and nowhere else so we use that to check for reruns.
 
 ; CHECK: PassManager{{.*}}SCC{{.*}} on (f1)
 ; CHECK: Running pass: BDCEPass on f1
 ; CHECK: PassManager{{.*}}SCC{{.*}} on (f2, f3)
 ; CHECK: Running pass: BDCEPass on f2
 ; CHECK-NOT: BDCEPass
 ; CHECK: PassManager{{.*}}SCC{{.*}} on (f2)
-; NORMAL: Running pass: BDCEPass on f2
+; RERUNSP: Running pass: BDCEPass on f2
 ; NORERUN-NOT: Running pass: BDCEPass on f2
 ; CHECK: PassManager{{.*}}SCC{{.*}} on (f3)
 ; CHECK: Running pass: BDCEPass on f3
 
 define void @f1(void()* %p) alwaysinline {
   call void %p()
   ret void
 }
 
 define void @f2() #0 {
   call void @f1(void()* @f2)
   call void @f3()
   ret void
 }
 
 define void @f3() #0 {
   call void @f2()
   ret void
 }
 
-attributes #0 = { nofree noreturn nosync nounwind readnone noinline }
+attributes #0 = { nofree noreturn nosync nounwind readnone noinline }