[PGO] Better handling of profile hash mismatch

[xur]

Summary

We currently assume profile hash conflicts will be caught by an upfront check and we assert for the cases that escape the check. The assumption is not always true as there are chances of conflict. This patch prints a warning and skips annotating the function for the escaped cases,.

[davidxl]

lib/Transforms/Instrumentation/PGOInstrumentation.cpp

1010 ↗

(On Diff #193368)

update the comments about the return value.

1042 ↗

(On Diff #193368)

document on how this can happen.

1155 ↗

(On Diff #193368)

What is the possible cause of it? It is better emit the information so that users can take some actions -- otherwise the message is not useful.

[xur]

lib/Transforms/Instrumentation/PGOInstrumentation.cpp

1155 ↗

(On Diff #193368)

this is profile mismatch, usually from stale profile (source change), or using the profile generated from other binaries. Is this the standard message for mismatch? We have the check here for the cases that escapes funchash conflict detection.

[davidxl]

lib/Transforms/Instrumentation/PGOInstrumentation.cpp

1155 ↗

(On Diff #193368)

When there is a hash conflict, it means the function name is also the same. Perhaps add more information: " the profile may be stale or there is a function name collision".

[xur]

Integrated David's comments.

llvm/trunk/lib/Transforms/Instrumentation/PGOInstrumentation.cpp

private:
   InstrProfRecord ProfileRecord;
 
   // Function hotness info derived from profile.
   FuncFreqAttr FreqAttr;
 
   // Is to use the context sensitive profile.
   bool IsCS;
 
-  // Find the Instrumented BB and set the value.
-  void setInstrumentedCounts(const std::vector<uint64_t> &CountFromProfile);
+  // Find the Instrumented BB and set the value. Return false on error.
+  bool setInstrumentedCounts(const std::vector<uint64_t> &CountFromProfile);
 
   // Set the edge counter value for the unknown edge -- there should be only
   // one unknown edge.
   void setEdgeCount(DirectEdges &Edges, uint64_t Value);
 
   // Return FuncName string;
   const std::string getFuncName() const { return FuncInfo.FuncName; }
 
void markFunctionAttributes(uint64_t EntryCount, uint64_t MaxCount) {
     else if (MaxCount <= ColdFunctionThreshold.scale(ProgramMaxCount))
       FreqAttr = FFA_Cold;
   }
 };
 
 } // end anonymous namespace
 
 // Visit all the edges and assign the count value for the instrumented
-// edges and the BB.
-void PGOUseFunc::setInstrumentedCounts(
+// edges and the BB. Return false on error.
+bool PGOUseFunc::setInstrumentedCounts(
     const std::vector<uint64_t> &CountFromProfile) {
-  assert(FuncInfo.getNumCounters() == CountFromProfile.size());
+  // The number of counters here should match the number of counters
+  // in profile. Return if they mismatch.
+  if (FuncInfo.getNumCounters() != 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);
for (auto &E : WorkList) {
     // 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;
+  return true;
 }
 
 // Set the count value for the unknown edge. There should be one and only one
 // unknown edge in Edges vector.
 void PGOUseFunc::setEdgeCount(DirectEdges &Edges, uint64_t Value) {
   for (auto &E : Edges) {
     if (E->CountValid)
       continue;
bool PGOUseFunc::readCounters(IndexedInstrProfReader *PGOReader, bool &AllZeros) {
   }
   AllZeros = (ValueSum == 0);
 
   LLVM_DEBUG(dbgs() << "SUM =  " << ValueSum << "\n");
 
   getBBInfo(nullptr).UnknownCountOutEdge = 2;
   getBBInfo(nullptr).UnknownCountInEdge = 2;
 
-  setInstrumentedCounts(CountFromProfile);
+  if (!setInstrumentedCounts(CountFromProfile)) {
+    LLVM_DEBUG(
+        dbgs() << "Inconsistent number of counts, skipping this function");
+    Ctx.diagnose(DiagnosticInfoPGOProfile(
+        M->getName().data(),
+        Twine("Inconsistent number of counts in ") + F.getName().str()
+        + Twine(": the profile may be stale or there is a function name collision."),
+        DS_Warning));
+    return false;
+  }
   ProgramMaxCount = PGOReader->getMaximumFunctionCount(IsCS);
   return true;
 }
 
 // Populate the counters from instrumented BBs to all BBs.
 // In the end of this operation, all BBs should have a valid count value.
 void PGOUseFunc::populateCounters() {
   // First set up Count variable for all BBs.

llvm/trunk/test/Transforms/PGOProfile/Inputs/select_hash_conflict.proftext

+# IR level Instrumentation Flag
+:ir
+foo
+# Func Hash:
[phone]
+# Num Counters:
+1
+# Counter Values:
+1
+

llvm/trunk/test/Transforms/PGOProfile/select_hash_conflict.ll

+; RUN: llvm-profdata merge %S/Inputs/select_hash_conflict.proftext -o %t.profdata
+; RUN: opt < %s -pgo-instr-use -pgo-test-profile-file=%t.profdata -pgo-instr-select=true -S | FileCheck %s
+; RUN: opt < %s -passes=pgo-instr-use -pgo-test-profile-file=%t.profdata -pgo-instr-select=true -S | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+@a = common dso_local local_unnamed_addr global [16 x i32] zeroinitializer, align 16
+@c0 = common dso_local local_unnamed_addr global i8 0, align 1
+@c1 = common dso_local local_unnamed_addr global i8 0, align 1
+@c2 = common dso_local local_unnamed_addr global i8 0, align 1
+@c3 = common dso_local local_unnamed_addr global i8 0, align 1
+@c4 = common dso_local local_unnamed_addr global i8 0, align 1
+@c5 = common dso_local local_unnamed_addr global i8 0, align 1
+@c6 = common dso_local local_unnamed_addr global i8 0, align 1
+@c7 = common dso_local local_unnamed_addr global i8 0, align 1
+@c8 = common dso_local local_unnamed_addr global i8 0, align 1
+@c9 = common dso_local local_unnamed_addr global i8 0, align 1
+@c10 = common dso_local local_unnamed_addr global i8 0, align 1
+@c11 = common dso_local local_unnamed_addr global i8 0, align 1
+@c12 = common dso_local local_unnamed_addr global i8 0, align 1
+@c13 = common dso_local local_unnamed_addr global i8 0, align 1
+@c14 = common dso_local local_unnamed_addr global i8 0, align 1
+@c15 = common dso_local local_unnamed_addr global i8 0, align 1
+
+define i32 @foo(i32 %n) {
+entry:
+  %0 = load i8, i8* @c0, align 1
+  %tobool = icmp eq i8 %0, 0
+  %cond = select i1 %tobool, i32 2, i32 1
+  store i32 %cond, i32* getelementptr inbounds ([16 x i32], [16 x i32]* @a, i64 0, i64 0), align 16
+  %1 = load i8, i8* @c1, align 1
+  %tobool2 = icmp eq i8 %1, 0
+  %cond3 = select i1 %tobool2, i32 2, i32 1
+  store i32 %cond3, i32* getelementptr inbounds ([16 x i32], [16 x i32]* @a, i64 0, i64 1), align 4
+  %2 = load i8, i8* @c2, align 1
+  %tobool5 = icmp eq i8 %2, 0
+  %cond6 = select i1 %tobool5, i32 2, i32 1
+  store i32 %cond6, i32* getelementptr inbounds ([16 x i32], [16 x i32]* @a, i64 0, i64 2), align 8
+  %3 = load i8, i8* @c3, align 1
+  %tobool8 = icmp eq i8 %3, 0
+  %cond9 = select i1 %tobool8, i32 2, i32 1
+  store i32 %cond9, i32* getelementptr inbounds ([16 x i32], [16 x i32]* @a, i64 0, i64 3), align 4
+  %4 = load i8, i8* @c4, align 1
+  %tobool11 = icmp eq i8 %4, 0
+  %cond12 = select i1 %tobool11, i32 2, i32 1
+  store i32 %cond12, i32* getelementptr inbounds ([16 x i32], [16 x i32]* @a, i64 0, i64 4), align 16
+  %5 = load i8, i8* @c5, align 1
+  %tobool14 = icmp eq i8 %5, 0
+  %cond15 = select i1 %tobool14, i32 2, i32 1
+  store i32 %cond15, i32* getelementptr inbounds ([16 x i32], [16 x i32]* @a, i64 0, i64 5), align 4
+  %6 = load i8, i8* @c6, align 1
+  %tobool17 = icmp eq i8 %6, 0
+  %cond18 = select i1 %tobool17, i32 2, i32 1
+  store i32 %cond18, i32* getelementptr inbounds ([16 x i32], [16 x i32]* @a, i64 0, i64 6), align 8
+  %7 = load i8, i8* @c7, align 1
+  %tobool20 = icmp eq i8 %7, 0
+  %cond21 = select i1 %tobool20, i32 2, i32 1
+  store i32 %cond21, i32* getelementptr inbounds ([16 x i32], [16 x i32]* @a, i64 0, i64 7), align 4
+  %8 = load i8, i8* @c8, align 1
+  %tobool23 = icmp eq i8 %8, 0
+  %cond24 = select i1 %tobool23, i32 2, i32 1
+  store i32 %cond24, i32* getelementptr inbounds ([16 x i32], [16 x i32]* @a, i64 0, i64 8), align 16
+  %9 = load i8, i8* @c9, align 1
+  %tobool26 = icmp eq i8 %9, 0
+  %cond27 = select i1 %tobool26, i32 2, i32 1
+  store i32 %cond27, i32* getelementptr inbounds ([16 x i32], [16 x i32]* @a, i64 0, i64 9), align 4
+  %10 = load i8, i8* @c10, align 1
+  %tobool29 = icmp eq i8 %10, 0
+  %cond30 = select i1 %tobool29, i32 2, i32 1
+  store i32 %cond30, i32* getelementptr inbounds ([16 x i32], [16 x i32]* @a, i64 0, i64 10), align 8
+  %11 = load i8, i8* @c11, align 1
+  %tobool32 = icmp eq i8 %11, 0
+  %cond33 = select i1 %tobool32, i32 2, i32 1
+  store i32 %cond33, i32* getelementptr inbounds ([16 x i32], [16 x i32]* @a, i64 0, i64 11), align 4
+  %12 = load i8, i8* @c12, align 1
+  %tobool35 = icmp eq i8 %12, 0
+  %cond36 = select i1 %tobool35, i32 2, i32 1
+  store i32 %cond36, i32* getelementptr inbounds ([16 x i32], [16 x i32]* @a, i64 0, i64 12), align 16
+  %13 = load i8, i8* @c13, align 1
+  %tobool38 = icmp eq i8 %13, 0
+  %cond39 = select i1 %tobool38, i32 2, i32 1
+  store i32 %cond39, i32* getelementptr inbounds ([16 x i32], [16 x i32]* @a, i64 0, i64 13), align 4
+  %14 = load i8, i8* @c14, align 1
+  %tobool41 = icmp eq i8 %14, 0
+  %cond42 = select i1 %tobool41, i32 2, i32 1
+  store i32 %cond42, i32* getelementptr inbounds ([16 x i32], [16 x i32]* @a, i64 0, i64 14), align 8
+  %15 = load i8, i8* @c15, align 1
+  %tobool44 = icmp eq i8 %15, 0
+  %cond45 = select i1 %tobool44, i32 2, i32 1
+  store i32 %cond45, i32* getelementptr inbounds ([16 x i32], [16 x i32]* @a, i64 0, i64 15), align 4
+  ret i32 %n
+}
+; CHECK-LABEL: define i32 @foo(i32 %n)
+; We should skip the profile.
+; CHECK-NOT: %{{.*}} = select i1 %{{.*}}, i32 2, i32 1, !prof
+