[CGSCC] Add pass which counts the max number of times we visit a function

This will help with finding potential pathological CGSCC cases.

Reviewed By: asbirlea

Differential Revision: https://reviews.llvm.org/D142853

llvm/include/llvm/Transforms/Utils/CountVisits.h

@@ -0,0 +1,28 @@
+//===- CountVisits.h --------------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_TRANSFORMS_UTILS_COUNT_VISITS_H
+#define LLVM_TRANSFORMS_UTILS_COUNT_VISITS_H
+
+#include "llvm/ADT/StringMap.h"
+#include "llvm/IR/PassManager.h"
+
+namespace llvm {
+
+class Function;
+
+struct CountVisitsPass : PassInfoMixin<CountVisitsPass> {
+  PreservedAnalyses run(Function &F, FunctionAnalysisManager &);
+
+private:
+  StringMap<uint32_t> Counts;
+};
+
+} // end namespace llvm
+
+#endif // LLVM_TRANSFORMS_UTILS_COUNT_VISITS_H

llvm/lib/Passes/PassBuilder.cpp

@@ -227,6 +227,7 @@
 #include "llvm/Transforms/Utils/BreakCriticalEdges.h"
 #include "llvm/Transforms/Utils/CanonicalizeAliases.h"
 #include "llvm/Transforms/Utils/CanonicalizeFreezeInLoops.h"
+#include "llvm/Transforms/Utils/CountVisits.h"
 #include "llvm/Transforms/Utils/Debugify.h"
 #include "llvm/Transforms/Utils/EntryExitInstrumenter.h"
 #include "llvm/Transforms/Utils/FixIrreducible.h"

llvm/lib/Passes/PassBuilderPipelines.cpp

@@ -118,6 +118,7 @@
 #include "llvm/Transforms/Utils/AddDiscriminators.h"
 #include "llvm/Transforms/Utils/AssumeBundleBuilder.h"
 #include "llvm/Transforms/Utils/CanonicalizeAliases.h"
+#include "llvm/Transforms/Utils/CountVisits.h"
 #include "llvm/Transforms/Utils/InjectTLIMappings.h"
 #include "llvm/Transforms/Utils/LibCallsShrinkWrap.h"
 #include "llvm/Transforms/Utils/Mem2Reg.h"
@@ -262,6 +263,11 @@ static cl::opt<bool>
     EnableMatrix("enable-matrix", cl::init(false), cl::Hidden,
                  cl::desc("Enable lowering of the matrix intrinsics"));
 
+static cl::opt<bool> CountCGSCCVisits(
+    "count-cgscc-max-visits", cl::init(false), cl::Hidden,
+    cl::desc("Keep track of the max number of times we visit a function in the "
+             "CGSCC pipeline as a statistic"));
+
 static cl::opt<bool> EnableConstraintElimination(
     "enable-constraint-elimination", cl::init(false), cl::Hidden,
     cl::desc(
@@ -322,6 +328,9 @@ PassBuilder::buildO1FunctionSimplificationPipeline(OptimizationLevel Level,
 
   FunctionPassManager FPM;
 
+  if (CountCGSCCVisits)
+    FPM.addPass(CountVisitsPass());
+
   // Form SSA out of local memory accesses after breaking apart aggregates into
   // scalars.
   FPM.addPass(SROAPass(SROAOptions::ModifyCFG));
@@ -472,6 +481,9 @@ PassBuilder::buildFunctionSimplificationPipeline(OptimizationLevel Level,
 
   FunctionPassManager FPM;
 
+  if (CountCGSCCVisits)
+    FPM.addPass(CountVisitsPass());
+
   // Form SSA out of local memory accesses after breaking apart aggregates into
   // scalars.
   FPM.addPass(SROAPass(SROAOptions::ModifyCFG));

llvm/lib/Passes/PassRegistry.def

@@ -273,6 +273,7 @@ FUNCTION_PASS("bounds-checking", BoundsCheckingPass())
 FUNCTION_PASS("break-crit-edges", BreakCriticalEdgesPass())
 FUNCTION_PASS("callsite-splitting", CallSiteSplittingPass())
 FUNCTION_PASS("consthoist", ConstantHoistingPass())
+FUNCTION_PASS("count-visits", CountVisitsPass())
 FUNCTION_PASS("constraint-elimination", ConstraintEliminationPass())
 FUNCTION_PASS("chr", ControlHeightReductionPass())
 FUNCTION_PASS("coro-elide", CoroElidePass())

llvm/lib/Transforms/Utils/CMakeLists.txt

@@ -17,6 +17,7 @@ add_llvm_component_library(LLVMTransformUtils
   CodeLayout.cpp
   CodeMoverUtils.cpp
   CtorUtils.cpp
+  CountVisits.cpp
   Debugify.cpp
   DemoteRegToStack.cpp
   EntryExitInstrumenter.cpp

llvm/lib/Transforms/Utils/CountVisits.cpp

@@ -0,0 +1,25 @@
+//===- CountVisits.cpp ----------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Utils/CountVisits.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/IR/PassManager.h"
+
+using namespace llvm;
+
+#define DEBUG_TYPE "count-visits"
+
+STATISTIC(MaxVisited, "Max number of times we visited a function");
+
+PreservedAnalyses CountVisitsPass::run(Function &F, FunctionAnalysisManager &) {
+  uint32_t Count = Counts[F.getName()] + 1;
+  Counts[F.getName()] = Count;
+  if (Count > MaxVisited)
+    MaxVisited = Count;
+  return PreservedAnalyses::all();
+}

llvm/test/Other/count-visits.ll

@@ -0,0 +1,20 @@
+; RUN: opt -passes=count-visits -stats 2>&1 -disable-output < %s | FileCheck %s --check-prefix=ONE
+; RUN: opt -passes='cgscc(count-visits)' -stats 2>&1 -disable-output < %s | FileCheck %s --check-prefix=ONE
+; RUN: opt -passes='cgscc(count-visits,instcombine)' -stats 2>&1 -disable-output < %s | FileCheck %s --check-prefix=TWO
+; RUN: opt -passes='default<O1>' -count-cgscc-max-visits -stats 2>&1 -disable-output < %s | FileCheck %s --check-prefix=PIPELINE
+; RUN: opt -passes='default<O3>' -count-cgscc-max-visits -stats 2>&1 -disable-output < %s | FileCheck %s --check-prefix=PIPELINE
+
+; ONE: 1 count-visits - Max number of times we visited a function
+; TWO: 2 count-visits - Max number of times we visited a function
+; PIPELINE: count-visits - Max number of times we visited a function
+
+define void @f() {
+  %a = bitcast ptr @g to ptr
+  call void %a()
+  ret void
+}
+
+define void @g() {
+  call void @f()
+  ret void
+}

llvm/utils/gn/secondary/llvm/lib/Transforms/Utils/BUILD.gn

@@ -11,6 +11,7 @@ static_library("Utils") {
     "ASanStackFrameLayout.cpp",
     "AddDiscriminators.cpp",
     "AssumeBundleBuilder.cpp",
+    "CountVisits.cpp",
     "BasicBlockUtils.cpp",
     "BreakCriticalEdges.cpp",
     "BuildLibCalls.cpp",