[PGO] Handle cases of failing to split critical edges

Fix PR41279 where critical edges to EHPad are not split.
The fix is to not instrument those critical edges. We used to be able to know
the size of counters right after MST is computed. With this, we have to
pre-collect the instrument BBs to know the size, and then instrument them.

Differential Revision: https://reviews.llvm.org/D62439

llvm-svn: 361882

1 files changed, 56 insertions, 44 deletions

diff --git a/llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp b/llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
index d5267a86e2d..6996e7a0502 100644
--- a/llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
+++ b/llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
@@ -573,6 +573,10 @@ public:
   // The Minimum Spanning Tree of function CFG.
   CFGMST<Edge, BBInfo> MST;
 
+  // Collect all the BBs that will be instrumented, and store them in
+  // InstrumentBBs.
+  void getInstrumentBBs(std::vector<BasicBlock *> &InstrumentBBs);
+
   // Give an edge, find the BB that will be instrumented.
   // Return nullptr if there is no BB to be instrumented.
   BasicBlock *getInstrBB(Edge *E);
@@ -629,16 +633,6 @@ public:
     if (CreateGlobalVar)
       FuncNameVar = createPGOFuncNameVar(F, FuncName);
   }
-
-  // Return the number of profile counters needed for the function.
-  unsigned getNumCounters() {
-    unsigned NumCounters = 0;
-    for (auto &E : this->MST.AllEdges) {
-      if (!E->InMST && !E->Removed)
-        NumCounters++;
-    }
-    return NumCounters + SIVisitor.getNumOfSelectInsts();
-  }
 };
 
 } // end anonymous namespace
@@ -753,6 +747,24 @@ void FuncPGOInstrumentation<Edge, BBInfo>::renameComdatFunction() {
   }
 }
 
+// Collect all the BBs that will be instruments and return them in
+// InstrumentBBs.
+template <class Edge, class BBInfo>
+void FuncPGOInstrumentation<Edge, BBInfo>::getInstrumentBBs(
+    std::vector<BasicBlock *> &InstrumentBBs) {
+  // Use a worklist as we will update the vector during the iteration.
+  std::vector<Edge *> EdgeList;
+  EdgeList.reserve(MST.AllEdges.size());
+  for (auto &E : MST.AllEdges)
+    EdgeList.push_back(E.get());
+
+  for (auto &E : EdgeList) {
+    BasicBlock *InstrBB = getInstrBB(E);
+    if (InstrBB)
+      InstrumentBBs.push_back(InstrBB);
+  }
+}
+
 // Given a CFG E to be instrumented, find which BB to place the instrumented
 // code. The function will split the critical edge if necessary.
 template <class Edge, class BBInfo>
@@ -783,9 +795,18 @@ BasicBlock *FuncPGOInstrumentation<Edge, BBInfo>::getInstrBB(Edge *E) {
                     << " --> " << getBBInfo(DestBB).Index << "\n");
   unsigned SuccNum = GetSuccessorNumber(SrcBB, DestBB);
   BasicBlock *InstrBB = SplitCriticalEdge(TI, SuccNum);
-  assert(InstrBB && "Critical edge is not split");
-
+  if (!InstrBB) {
+    LLVM_DEBUG(
+        dbgs() << "Fail to split critical edge: not instrument this edge.\n");
+    return nullptr;
+  }
+  // Need to add two new edges. First one: Add new edge of SrcBB->InstrBB.
+  MST.addEdge(SrcBB, InstrBB, 0);
+  // Second one: Add new edge of InstrBB->DestBB.
+  Edge &NewEdge1 = MST.addEdge(InstrBB, DestBB, 0);
+  NewEdge1.InMST = true;
   E->Removed = true;
+
   return InstrBB;
 }
 
@@ -801,15 +822,14 @@ static void instrumentOneFunc(
 
   FuncPGOInstrumentation<PGOEdge, BBInfo> FuncInfo(F, ComdatMembers, true, BPI,
                                                    BFI, IsCS);
-  unsigned NumCounters = FuncInfo.getNumCounters();
+  std::vector<BasicBlock *> InstrumentBBs;
+  FuncInfo.getInstrumentBBs(InstrumentBBs);
+  unsigned NumCounters =
+      InstrumentBBs.size() + FuncInfo.SIVisitor.getNumOfSelectInsts();
 
   uint32_t I = 0;
   Type *I8PtrTy = Type::getInt8PtrTy(M->getContext());
-  for (auto &E : FuncInfo.MST.AllEdges) {
-    BasicBlock *InstrBB = FuncInfo.getInstrBB(E.get());
-    if (!InstrBB)
-      continue;
-
+  for (auto *InstrBB : InstrumentBBs) {
     IRBuilder<> Builder(InstrBB, InstrBB->getFirstInsertionPt());
     assert(Builder.GetInsertPoint() != InstrBB->end() &&
            "Cannot get the Instrumentation point");
@@ -1039,39 +1059,31 @@ private:
 // edges and the BB. Return false on error.
 bool PGOUseFunc::setInstrumentedCounts(
     const std::vector<uint64_t> &CountFromProfile) {
+
+  std::vector<BasicBlock *> InstrumentBBs;
+  FuncInfo.getInstrumentBBs(InstrumentBBs);
+  unsigned NumCounters =
+      InstrumentBBs.size() + FuncInfo.SIVisitor.getNumOfSelectInsts();
   // The number of counters here should match the number of counters
   // in profile. Return if they mismatch.
-  if (FuncInfo.getNumCounters() != CountFromProfile.size()) {
+  if (NumCounters != CountFromProfile.size()) {
     return false;
   }
-  // Use a worklist as we will update the vector during the iteration.
-  std::vector<PGOUseEdge *> WorkList;
-  for (auto &E : FuncInfo.MST.AllEdges)
-    WorkList.push_back(E.get());
-
   uint32_t I = 0;
-  for (auto &E : WorkList) {
-    BasicBlock *InstrBB = FuncInfo.getInstrBB(E);
-    if (!InstrBB)
-      continue;
+  for (BasicBlock *InstrBB : InstrumentBBs) {
     uint64_t CountValue = CountFromProfile[I++];
-    if (!E->Removed) {
-      getBBInfo(InstrBB).setBBInfoCount(CountValue);
-      E->setEdgeCount(CountValue);
-      continue;
+    UseBBInfo &Info = getBBInfo(InstrBB);
+    Info.setBBInfoCount(CountValue);
+    // If only one in-edge, the edge profile count should be the same as BB
+    // profile count.
+    if (Info.InEdges.size() == 1) {
+      Info.InEdges[0]->setEdgeCount(CountValue);
+    }
+    // If only one out-edge, the edge profile count should be the same as BB
+    // profile count.
+    if (Info.OutEdges.size() == 1) {
+      Info.OutEdges[0]->setEdgeCount(CountValue);
     }
-
-    // Need to add two new edges.
-    BasicBlock *SrcBB = const_cast<BasicBlock *>(E->SrcBB);
-    BasicBlock *DestBB = const_cast<BasicBlock *>(E->DestBB);
-    // Add new edge of SrcBB->InstrBB.
-    PGOUseEdge &NewEdge = FuncInfo.MST.addEdge(SrcBB, InstrBB, 0);
-    NewEdge.setEdgeCount(CountValue);
-    // Add new edge of InstrBB->DestBB.
-    PGOUseEdge &NewEdge1 = FuncInfo.MST.addEdge(InstrBB, DestBB, 0);
-    NewEdge1.setEdgeCount(CountValue);
-    NewEdge1.InMST = true;
-    getBBInfo(InstrBB).setBBInfoCount(CountValue);
   }
   ProfileCountSize = CountFromProfile.size();
   CountPosition = I;