[Attributor] Add AAExecutionDomainInfo interface to OpenMPOpt

Summary:
Add the AAExecutionDomainInfo attributor instance to OpenMPOpt.
This will infer information relating to domain information that an
instruction might be expecting in. Right now this only includes a very
crude check for instructions that will be executed by the master thread
by comparing a thread-id function with a constant zero.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D101578

lib/Transforms/IPO/OpenMPOpt.cpp

@@ -15,6 +15,7 @@
 #include "llvm/Transforms/IPO/OpenMPOpt.h"
 
 #include "llvm/ADT/EnumeratedArray.h"
+#include "llvm/ADT/PostOrderIterator.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/Analysis/CallGraph.h"
 #include "llvm/Analysis/CallGraphSCCPass.h"
@@ -78,6 +79,36 @@ static constexpr auto TAG = "[" DEBUG_TYPE "]";
 
 namespace {
 
+struct AAExecutionDomain
+    : public StateWrapper<BooleanState, AbstractAttribute> {
+  using Base = StateWrapper<BooleanState, AbstractAttribute>;
+  AAExecutionDomain(const IRPosition &IRP, Attributor &A) : Base(IRP) {}
+
+  /// Create an abstract attribute view for the position \p IRP.
+  static AAExecutionDomain &createForPosition(const IRPosition &IRP,
+                                              Attributor &A);
+
+  /// See AbstractAttribute::getName().
+  const std::string getName() const override { return "AAExecutionDomain"; }
+
+  /// See AbstractAttribute::getIdAddr().
+  const char *getIdAddr() const override { return &ID; }
+
+  /// Check if an instruction is executed by a single thread.
+  virtual bool isSingleThreadExecution(const Instruction &) const = 0;
+
+  virtual bool isSingleThreadExecution(const BasicBlock &) const = 0;
+
+  /// This function should return true if the type of the \p AA is
+  /// AAExecutionDomain.
+  static bool classof(const AbstractAttribute *AA) {
+    return (AA->getIdAddr() == &ID);
+  }
+
+  /// Unique ID (due to the unique address)
+  static const char ID;
+};
+
 struct AAICVTracker;
 
 /// OpenMP specific information. For now, stores RFIs and ICVs also needed for
@@ -506,6 +537,8 @@ struct OpenMPOpt {
                       << OMPInfoCache.ModuleSlice.size() << " functions\n");
 
     if (IsModulePass) {
+      Changed |= runAttributor();
+
       if (remarksEnabled())
         analysisGlobalization();
     } else {
@@ -1606,6 +1639,11 @@ private:
 
       GetterRFI.foreachUse(SCC, CreateAA);
     }
+
+    for (auto &F : M) {
+      if (!F.isDeclaration())
+        A.getOrCreateAAFor<AAExecutionDomain>(IRPosition::function(F));
+    }
   }
 };
 
@@ -2244,9 +2282,136 @@ struct AAICVTrackerCallSiteReturned : AAICVTracker {
     return Changed;
   }
 };
+
+struct AAExecutionDomainFunction : public AAExecutionDomain {
+  AAExecutionDomainFunction(const IRPosition &IRP, Attributor &A)
+      : AAExecutionDomain(IRP, A) {}
+
+  const std::string getAsStr() const override {
+    return "[AAExecutionDomain] " + std::to_string(SingleThreadedBBs.size()) +
+           "/" + std::to_string(NumBBs) + " BBs thread 0 only.";
+  }
+
+  /// See AbstractAttribute::trackStatistics().
+  void trackStatistics() const override {}
+
+  void initialize(Attributor &A) override {
+    Function *F = getAnchorScope();
+    for (const auto &BB : *F)
+      SingleThreadedBBs.insert(&BB);
+    NumBBs = SingleThreadedBBs.size();
+  }
+
+  ChangeStatus manifest(Attributor &A) override {
+    LLVM_DEBUG({
+      for (const BasicBlock *BB : SingleThreadedBBs)
+        dbgs() << TAG << " Basic block @" << getAnchorScope()->getName() << " "
+               << BB->getName() << " is executed by a single thread.\n";
+    });
+    return ChangeStatus::UNCHANGED;
+  }
+
+  ChangeStatus updateImpl(Attributor &A) override;
+
+  /// Check if an instruction is executed by a single thread.
+  bool isSingleThreadExecution(const Instruction &I) const override {
+    return isSingleThreadExecution(*I.getParent());
+  }
+
+  bool isSingleThreadExecution(const BasicBlock &BB) const override {
+    return SingleThreadedBBs.contains(&BB);
+  }
+
+  /// Set of basic blocks that are executed by a single thread.
+  DenseSet<const BasicBlock *> SingleThreadedBBs;
+
+  /// Total number of basic blocks in this function.
+  long unsigned NumBBs;
+};
+
+ChangeStatus AAExecutionDomainFunction::updateImpl(Attributor &A) {
+  auto &OMPInfoCache = static_cast<OMPInformationCache &>(A.getInfoCache());
+  Function *F = getAnchorScope();
+  ReversePostOrderTraversal<Function *> RPOT(F);
+  auto NumSingleThreadedBBs = SingleThreadedBBs.size();
+
+  bool AllCallSitesKnown;
+  auto PredForCallSite = [&](AbstractCallSite ACS) {
+    const auto &ExecutionDomainAA = A.getAAFor<AAExecutionDomain>(
+        *this, IRPosition::function(*ACS.getInstruction()->getFunction()),
+        DepClassTy::REQUIRED);
+    return ExecutionDomainAA.isSingleThreadExecution(*ACS.getInstruction());
+  };
+
+  if (!A.checkForAllCallSites(PredForCallSite, *this,
+                              /* RequiresAllCallSites */ true,
+                              AllCallSitesKnown))
+    SingleThreadedBBs.erase(&F->getEntryBlock());
+
+  // Check if the edge into the successor block compares a thread-id function to
+  // a constant zero.
+  // TODO: Use AAValueSimplify to simplify and propogate constants.
+  // TODO: Check more than a single use for thread ID's.
+  auto IsSingleThreadOnly = [&](BranchInst *Edge, BasicBlock *SuccessorBB) {
+    if (!Edge || !Edge->isConditional())
+      return false;
+    if (Edge->getSuccessor(0) != SuccessorBB)
+      return false;
+
+    auto *Cmp = dyn_cast<CmpInst>(Edge->getCondition());
+    if (!Cmp || !Cmp->isTrueWhenEqual() || !Cmp->isEquality())
+      return false;
+
+    ConstantInt *C = dyn_cast<ConstantInt>(Cmp->getOperand(1));
+    if (!C || !C->isZero())
+      return false;
+
+    if (auto *CB = dyn_cast<CallBase>(Cmp->getOperand(0))) {
+      RuntimeFunction ThreadNumRuntimeIDs[] = {OMPRTL_omp_get_thread_num,
+                                               OMPRTL___kmpc_master,
+                                               OMPRTL___kmpc_global_thread_num};
+
+      for (const auto ThreadNumRuntimeID : ThreadNumRuntimeIDs) {
+        auto &RFI = OMPInfoCache.RFIs[ThreadNumRuntimeID];
+        if (CB->getCalledFunction() == RFI.Declaration)
+          return true;
+      }
+    }
+
+    return false;
+  };
+
+  // Merge all the predecessor states into the current basic block. A basic
+  // block is executed by a single thread if all of its predecessors are.
+  auto MergePredecessorStates = [&](BasicBlock *BB) {
+    if (pred_begin(BB) == pred_end(BB))
+      return SingleThreadedBBs.contains(BB);
+
+    bool IsSingleThreaded = true;
+    for (auto PredBB = pred_begin(BB), PredEndBB = pred_end(BB);
+         PredBB != PredEndBB; ++PredBB) {
+      if (!IsSingleThreadOnly(dyn_cast<BranchInst>((*PredBB)->getTerminator()),
+                              BB))
+        IsSingleThreaded &= SingleThreadedBBs.contains(*PredBB);
+    }
+
+    return IsSingleThreaded;
+  };
+
+  for (auto *BB : RPOT) {
+    if (!MergePredecessorStates(BB))
+      SingleThreadedBBs.erase(BB);
+  }
+
+  return (NumSingleThreadedBBs == SingleThreadedBBs.size())
+             ? ChangeStatus::UNCHANGED
+             : ChangeStatus::CHANGED;
+}
+
 } // namespace
 
 const char AAICVTracker::ID = 0;
+const char AAExecutionDomain::ID = 0;
 
 AAICVTracker &AAICVTracker::createForPosition(const IRPosition &IRP,
                                               Attributor &A) {
@@ -2274,6 +2439,27 @@ AAICVTracker &AAICVTracker::createForPosition(const IRPosition &IRP,
   return *AA;
 }
 
+AAExecutionDomain &AAExecutionDomain::createForPosition(const IRPosition &IRP,
+                                                        Attributor &A) {
+  AAExecutionDomainFunction *AA = nullptr;
+  switch (IRP.getPositionKind()) {
+  case IRPosition::IRP_INVALID:
+  case IRPosition::IRP_FLOAT:
+  case IRPosition::IRP_ARGUMENT:
+  case IRPosition::IRP_CALL_SITE_ARGUMENT:
+  case IRPosition::IRP_RETURNED:
+  case IRPosition::IRP_CALL_SITE_RETURNED:
+  case IRPosition::IRP_CALL_SITE:
+    llvm_unreachable(
+        "AAExecutionDomain can only be created for function position!");
+  case IRPosition::IRP_FUNCTION:
+    AA = new (A.Allocator) AAExecutionDomainFunction(IRP, A);
+    break;
+  }
+
+  return *AA;
+}
+
 PreservedAnalyses OpenMPOptPass::run(Module &M, ModuleAnalysisManager &AM) {
   if (!containsOpenMP(M, OMPInModule))
     return PreservedAnalyses::all();

test/Transforms/OpenMP/single_threaded_execution.ll

@@ -0,0 +1,43 @@
+; RUN: opt -passes=openmp-opt-cgscc -debug-only=openmp-opt -disable-output < %s 2>&1 | FileCheck %s
+; ModuleID = 'single_threaded_exeuction.c'
+
+%struct.ident_t = type { i32, i32, i32, i32, i8* }
+
+@.str = private unnamed_addr constant [4 x i8] c"%d\0A\00", align 1
+@0 = private unnamed_addr constant [23 x i8] c";unknown;unknown;0;0;;\00", align 1
+@1 = private unnamed_addr constant %struct.ident_t { i32 0, i32 2, i32 0, i32 0, i8* getelementptr inbounds ([23 x i8], [23 x i8]* @0, i32 0, i32 0) }, align 8
+
+; CHECK: [openmp-opt] Basic block @bar entry is executed by a single thread.
+; Function Attrs: noinline nounwind uwtable
+define internal void @bar() {
+entry:
+  ret void
+}
+
+; CHECK-NOT: [openmp-opt] Basic block @foo entry is executed by a single thread.
+; CHECK: [openmp-opt] Basic block @foo if.then is executed by a single thread.
+; CHECK-NOT: [openmp-opt] Basic block @foo if.end is executed by a single thread.
+; Function Attrs: noinline nounwind uwtable
+define dso_local void @foo() {
+entry:
+  %call = call i32 @omp_get_thread_num()
+  %cmp = icmp eq i32 %call, 0
+  br i1 %cmp, label %if.then, label %if.end
+
+if.then:
+  call void @bar()
+  br label %if.end
+
+if.end:
+  ret void
+}
+
+declare dso_local i32 @omp_get_thread_num()
+
+!llvm.module.flags = !{!0}
+!llvm.ident = !{!1}
+
+!0 = !{i32 1, !"wchar_size", i32 4}
+!1 = !{!"clang version 13.0.0"}
+!2 = !{!3}
+!3 = !{i64 2, i64 -1, i64 -1, i1 true}