paulkirth updated this revision to Diff 215734.
paulkirth added a comment.

Remove frontend components of clang-misexpect in favor of backend 
implementations


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D66324/new/

https://reviews.llvm.org/D66324

Files:
  clang/include/clang/Basic/DiagnosticFrontendKinds.td
  clang/include/clang/Basic/DiagnosticGroups.td
  clang/lib/CodeGen/CodeGenAction.cpp
  clang/lib/CodeGen/CodeGenFunction.cpp
  clang/test/Profile/Inputs/misexpect-branch-nonconst-expect-arg.proftext
  clang/test/Profile/Inputs/misexpect-branch.proftext
  clang/test/Profile/Inputs/misexpect-switch-default-only.proftext
  clang/test/Profile/Inputs/misexpect-switch.proftext
  clang/test/Profile/misexpect-branch-cold.c
  clang/test/Profile/misexpect-branch-nonconst-expected-val.c
  clang/test/Profile/misexpect-branch.c
  clang/test/Profile/misexpect-no-warning-without-flag.c
  clang/test/Profile/misexpect-switch-default.c
  clang/test/Profile/misexpect-switch-nonconst.c
  clang/test/Profile/misexpect-switch-only-default-case.c
  clang/test/Profile/misexpect-switch.c
  llvm/include/llvm/IR/DiagnosticInfo.h
  llvm/include/llvm/IR/FixedMetadataKinds.def
  llvm/include/llvm/IR/MDBuilder.h
  llvm/include/llvm/Transforms/Utils/MisExpect.h
  llvm/lib/IR/DiagnosticInfo.cpp
  llvm/lib/IR/MDBuilder.cpp
  llvm/lib/Transforms/IPO/SampleProfile.cpp
  llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
  llvm/lib/Transforms/Scalar/LowerExpectIntrinsic.cpp
  llvm/lib/Transforms/Utils/CMakeLists.txt
  llvm/lib/Transforms/Utils/MisExpect.cpp
  llvm/test/ThinLTO/X86/lazyload_metadata.ll
  llvm/test/Transforms/LowerExpectIntrinsic/basic.ll

Index: llvm/test/Transforms/LowerExpectIntrinsic/basic.ll
===================================================================
--- llvm/test/Transforms/LowerExpectIntrinsic/basic.ll
+++ llvm/test/Transforms/LowerExpectIntrinsic/basic.ll
@@ -138,7 +138,7 @@
   %conv1 = sext i32 %conv to i64
   %expval = call i64 @llvm.expect.i64(i64 %conv1, i64 0)
   %tobool = icmp ne i64 %expval, 0
-; CHECK: !prof !1
+; CHECK: !prof !2
 ; CHECK-NOT: @llvm.expect
   br i1 %tobool, label %if.then, label %if.end
 
@@ -165,7 +165,7 @@
   %tmp = load i32, i32* %x.addr, align 4
   %conv = sext i32 %tmp to i64
   %expval = call i64 @llvm.expect.i64(i64 %conv, i64 1)
-; CHECK: !prof !2
+; CHECK: !prof !4
 ; CHECK-NOT: @llvm.expect
   switch i64 %expval, label %sw.epilog [
     i64 1, label %sw.bb
@@ -194,7 +194,7 @@
   %tmp = load i32, i32* %x.addr, align 4
   %conv = sext i32 %tmp to i64
   %expval = call i64 @llvm.expect.i64(i64 %conv, i64 1)
-; CHECK: !prof !3
+; CHECK: !prof !5
 ; CHECK-NOT: @llvm.expect
   switch i64 %expval, label %sw.epilog [
     i64 2, label %sw.bb
@@ -278,7 +278,7 @@
   %t7 = call i64 @llvm.expect.i64(i64 %t6, i64 0)
   %t8 = icmp ne i64 %t7, 0
   %t9 = select i1 %t8, i32 1, i32 2
-; CHECK: select{{.*}}, !prof !1
+; CHECK: select{{.*}}, !prof !2
   ret i32 %t9
 }
 
@@ -286,6 +286,6 @@
 declare i1 @llvm.expect.i1(i1, i1) nounwind readnone
 
 ; CHECK: !0 = !{!"branch_weights", i32 2000, i32 1}
-; CHECK: !1 = !{!"branch_weights", i32 1, i32 2000}
-; CHECK: !2 = !{!"branch_weights", i32 1, i32 2000, i32 1}
-; CHECK: !3 = !{!"branch_weights", i32 2000, i32 1, i32 1}
+; CHECK: !2 = !{!"branch_weights", i32 1, i32 2000}
+; CHECK: !4 = !{!"branch_weights", i32 1, i32 2000, i32 1}
+; CHECK: !5 = !{!"branch_weights", i32 2000, i32 1, i32 1}
Index: llvm/test/ThinLTO/X86/lazyload_metadata.ll
===================================================================
--- llvm/test/ThinLTO/X86/lazyload_metadata.ll
+++ llvm/test/ThinLTO/X86/lazyload_metadata.ll
@@ -10,13 +10,13 @@
 ; RUN: llvm-lto -thinlto-action=import %t2.bc -thinlto-index=%t3.bc \
 ; RUN:          -o /dev/null -stats \
 ; RUN:  2>&1 | FileCheck %s -check-prefix=LAZY
-; LAZY: 61 bitcode-reader  - Number of Metadata records loaded
+; LAZY: 63 bitcode-reader  - Number of Metadata records loaded
 ; LAZY: 2 bitcode-reader  - Number of MDStrings loaded
 
 ; RUN: llvm-lto -thinlto-action=import %t2.bc -thinlto-index=%t3.bc \
 ; RUN:          -o /dev/null -disable-ondemand-mds-loading -stats \
 ; RUN:  2>&1 | FileCheck %s -check-prefix=NOTLAZY
-; NOTLAZY: 70 bitcode-reader  - Number of Metadata records loaded
+; NOTLAZY: 72 bitcode-reader  - Number of Metadata records loaded
 ; NOTLAZY: 7 bitcode-reader  - Number of MDStrings loaded
 
 
Index: llvm/lib/Transforms/Utils/MisExpect.cpp
===================================================================
--- /dev/null
+++ llvm/lib/Transforms/Utils/MisExpect.cpp
@@ -0,0 +1,125 @@
+//===--- MisExpect.cpp - Check Use of __builtin_expect() with PGO data ----===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// This contains code to emit warnings for potentially incorrect usage of
+// __builtin_expect(). This utility extracts the threshold values from metadata
+// associated with the instrumented Branch or Switch. The threshold values are
+// then used to determin if a warning would be emmited.
+//
+// MisExpect metadata is generated when llvm.expect intrinsics are lowered see
+// LowerExpectIntrinsic.cpp
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Utils/MisExpect.h"
+#include "llvm/ADT/Twine.h"
+#include "llvm/IR/DiagnosticInfo.h"
+#include "llvm/IR/Instruction.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/Support/BranchProbability.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/FormatVariadic.h"
+#include <bits/stdint-uintn.h>
+#include <numeric>
+
+#define DEBUG_TYPE "misexpect"
+
+using namespace llvm;
+using namespace misexpect;
+
+namespace {
+
+Instruction *getOprndOrInst(Instruction *I) {
+  Instruction *Ret = nullptr;
+  if (auto B = dyn_cast<BranchInst>(I)) {
+    Ret = dyn_cast<Instruction>(B->getCondition());
+  } else if (auto S = dyn_cast<SwitchInst>(I)) {
+    Ret = dyn_cast<Instruction>(S->getCondition());
+  }
+  return Ret ? Ret : I;
+}
+
+void emitMisexpectDiagnostic(Instruction *I, LLVMContext &Ctx,
+                             double PercentageCorrect) {
+  auto PerString = formatv("{0:P}", PercentageCorrect);
+  Twine Msg(PerString);
+  Instruction *Cond = getOprndOrInst(I);
+  Ctx.diagnose(DiagnosticInfoMisExpect(Cond, Msg));
+}
+
+} // namespace
+
+namespace llvm {
+namespace misexpect {
+
+void verifyMisExpect(Instruction *I, const SmallVector<uint32_t, 4> &Weights,
+                     LLVMContext &Ctx) {
+  if (auto *MisExpectData = I->getMetadata(LLVMContext::MD_misexpect)) {
+    auto *MisExpectDataName = dyn_cast<MDString>(MisExpectData->getOperand(0));
+    if (MisExpectDataName &&
+        MisExpectDataName->getString().equals("misexpect")) {
+      LLVM_DEBUG(llvm::dbgs() << "------------------\n");
+      LLVM_DEBUG(llvm::dbgs()
+                 << "Function: " << I->getFunction()->getName() << "\n");
+      LLVM_DEBUG(llvm::dbgs() << "Instruction: " << *I << ":\n");
+      LLVM_DEBUG(for (int Idx = 0, Size = Weights.size(); Idx < Size; ++Idx) {
+        llvm::dbgs() << "Weights[" << Idx << "] = " << Weights[Idx] << "\n";
+      });
+      LLVM_DEBUG(llvm::dbgs() << "------------------\n");
+
+      // extract values from misexpect metadata
+      auto *C = mdconst::dyn_extract<ConstantInt>(MisExpectData->getOperand(1));
+      auto *L = mdconst::dyn_extract<ConstantInt>(MisExpectData->getOperand(2));
+      auto *U = mdconst::dyn_extract<ConstantInt>(MisExpectData->getOperand(3));
+
+      uint64_t Index = C->getValue().getZExtValue();
+      uint64_t LikelyBranchWeight = L->getValue().getZExtValue();
+      uint64_t UnlikelyBranchWeight = U->getValue().getZExtValue();
+      uint64_t ProfileCount = Weights[Index];
+      uint64_t CaseTotal =
+          std::accumulate(Weights.begin(), Weights.end(), (uint64_t)0,
+                          [](uint64_t W1, uint64_t W2) { return W1 + W2; });
+      int NumUnlikelyTargets = Weights.size() - 2;
+
+      const uint64_t TotalBranchWeight =
+          LikelyBranchWeight + (UnlikelyBranchWeight * NumUnlikelyTargets);
+
+      double Percentage = ((double)ProfileCount / (double)CaseTotal);
+
+      const llvm::BranchProbability LikelyThreshold(LikelyBranchWeight,
+                                                    TotalBranchWeight);
+      auto ScaledThreshold = LikelyThreshold.scale(CaseTotal);
+
+      if (ProfileCount < ScaledThreshold)
+        emitMisexpectDiagnostic(I, Ctx, Percentage);
+    }
+  }
+}
+
+void checkClangInstrumentation(Instruction &I) {
+  if (auto *MD = I.getMetadata(LLVMContext::MD_prof)) {
+    unsigned NOps = MD->getNumOperands();
+    // Operand 0 is a string tag "VP":
+    if (MDString *Tag = cast<MDString>(MD->getOperand(0))) {
+      if (NOps > 1 && Tag->getString().equals("branch_weights")) {
+        SmallVector<uint32_t, 4> RealWeights(NOps - 1);
+        for (unsigned i = 1; i < NOps; i++) {
+          ConstantInt *Value =
+              mdconst::dyn_extract<ConstantInt>(MD->getOperand(i));
+          RealWeights[i - 1] = Value->getZExtValue();
+        }
+        misexpect::verifyMisExpect(&I, RealWeights, I.getParent()->getParent()->getContext());
+      }
+    }
+  }
+}
+
+} // namespace misexpect
+} // namespace llvm
+#undef DEBUG_TYPE
Index: llvm/lib/Transforms/Utils/CMakeLists.txt
===================================================================
--- llvm/lib/Transforms/Utils/CMakeLists.txt
+++ llvm/lib/Transforms/Utils/CMakeLists.txt
@@ -40,6 +40,7 @@
   LowerSwitch.cpp
   Mem2Reg.cpp
   MetaRenamer.cpp
+  MisExpect.cpp
   ModuleUtils.cpp
   NameAnonGlobals.cpp
   PredicateInfo.cpp
Index: llvm/lib/Transforms/Scalar/LowerExpectIntrinsic.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/LowerExpectIntrinsic.cpp
+++ llvm/lib/Transforms/Scalar/LowerExpectIntrinsic.cpp
@@ -26,6 +26,7 @@
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Transforms/Scalar.h"
+#include "llvm/Transforms/Utils/MisExpect.h"
 
 using namespace llvm;
 
@@ -71,15 +72,20 @@
   unsigned n = SI.getNumCases(); // +1 for default case.
   SmallVector<uint32_t, 16> Weights(n + 1, UnlikelyBranchWeight);
 
-  if (Case == *SI.case_default())
-    Weights[0] = LikelyBranchWeight;
-  else
-    Weights[Case.getCaseIndex() + 1] = LikelyBranchWeight;
+  uint64_t Index = (Case == *SI.case_default()) ? 0 : Case.getCaseIndex() + 1;
+  Weights[Index] = LikelyBranchWeight;
+
+  SI.setMetadata(
+      LLVMContext::MD_misexpect,
+      MDBuilder(CI->getContext())
+          .createMisExpect(Index, LikelyBranchWeight, UnlikelyBranchWeight));
+
+  SI.setCondition(ArgValue);
+  misexpect::checkClangInstrumentation(SI);
 
   SI.setMetadata(LLVMContext::MD_prof,
                  MDBuilder(CI->getContext()).createBranchWeights(Weights));
 
-  SI.setCondition(ArgValue);
   return true;
 }
 
@@ -280,19 +286,28 @@
 
   MDBuilder MDB(CI->getContext());
   MDNode *Node;
+  MDNode *ExpNode;
 
   if ((ExpectedValue->getZExtValue() == ValueComparedTo) ==
-      (Predicate == CmpInst::ICMP_EQ))
+      (Predicate == CmpInst::ICMP_EQ)) {
     Node = MDB.createBranchWeights(LikelyBranchWeight, UnlikelyBranchWeight);
-  else
+    ExpNode = MDB.createMisExpect(0, LikelyBranchWeight, UnlikelyBranchWeight);
+  } else {
     Node = MDB.createBranchWeights(UnlikelyBranchWeight, LikelyBranchWeight);
+    ExpNode = MDB.createMisExpect(1, LikelyBranchWeight, UnlikelyBranchWeight);
+  }
 
-  BSI.setMetadata(LLVMContext::MD_prof, Node);
+  BSI.setMetadata(LLVMContext::MD_misexpect, ExpNode);
 
   if (CmpI)
     CmpI->setOperand(0, ArgValue);
   else
     BSI.setCondition(ArgValue);
+
+  misexpect::checkClangInstrumentation(BSI);
+
+  BSI.setMetadata(LLVMContext::MD_prof, Node);
+
   return true;
 }
 
Index: llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
===================================================================
--- llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
+++ llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
@@ -108,6 +108,7 @@
 #include "llvm/Transforms/Instrumentation.h"
 #include "llvm/Transforms/Instrumentation/PGOInstrumentation.h"
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
+#include "llvm/Transforms/Utils/MisExpect.h"
 #include <algorithm>
 #include <cassert>
 #include <cstdint>
@@ -1776,6 +1777,9 @@
                                            : Weights) {
     dbgs() << W << " ";
   } dbgs() << "\n";);
+
+  misexpect::verifyMisExpect(TI, Weights, TI->getContext());
+
   TI->setMetadata(LLVMContext::MD_prof, MDB.createBranchWeights(Weights));
   if (EmitBranchProbability) {
     std::string BrCondStr = getBranchCondString(TI);
Index: llvm/lib/Transforms/IPO/SampleProfile.cpp
===================================================================
--- llvm/lib/Transforms/IPO/SampleProfile.cpp
+++ llvm/lib/Transforms/IPO/SampleProfile.cpp
@@ -72,6 +72,7 @@
 #include "llvm/Transforms/Instrumentation.h"
 #include "llvm/Transforms/Utils/CallPromotionUtils.h"
 #include "llvm/Transforms/Utils/Cloning.h"
+#include "llvm/Transforms/Utils/MisExpect.h"
 #include <algorithm>
 #include <cassert>
 #include <cstdint>
@@ -1447,6 +1448,8 @@
       }
     }
 
+    misexpect::verifyMisExpect(TI, Weights, TI->getContext());
+
     uint64_t TempWeight;
     // Only set weights if there is at least one non-zero weight.
     // In any other case, let the analyzer set weights.
Index: llvm/lib/IR/MDBuilder.cpp
===================================================================
--- llvm/lib/IR/MDBuilder.cpp
+++ llvm/lib/IR/MDBuilder.cpp
@@ -309,3 +309,15 @@
   };
   return MDNode::get(Context, Vals);
 }
+
+MDNode *MDBuilder::createMisExpect(uint64_t Index, uint64_t LikleyWeight,
+                                   uint64_t UnlikleyWeight) {
+  auto IntType = Type::getInt64Ty(Context);
+  Metadata *Vals[] = {
+      createString("misexpect"),
+      createConstant(ConstantInt::get(IntType, Index)),
+      createConstant(ConstantInt::get(IntType, LikleyWeight)),
+      createConstant(ConstantInt::get(IntType, UnlikleyWeight)),
+  };
+  return MDNode::get(Context, Vals);
+}
Index: llvm/lib/IR/DiagnosticInfo.cpp
===================================================================
--- llvm/lib/IR/DiagnosticInfo.cpp
+++ llvm/lib/IR/DiagnosticInfo.cpp
@@ -370,5 +370,16 @@
   return OS.str();
 }
 
+DiagnosticInfoMisExpect::DiagnosticInfoMisExpect(const Instruction *Inst,
+                                                 Twine &Msg)
+    : DiagnosticInfoWithLocationBase(DK_MisExpect, DS_Warning,
+                                     *Inst->getParent()->getParent(),
+                                     Inst->getDebugLoc()),
+      Msg(Msg) {}
+
+void DiagnosticInfoMisExpect::print(DiagnosticPrinter &DP) const {
+  DP << getLocationStr() << ": " << getMsg();
+}
+
 void OptimizationRemarkAnalysisFPCommute::anchor() {}
 void OptimizationRemarkAnalysisAliasing::anchor() {}
Index: llvm/include/llvm/Transforms/Utils/MisExpect.h
===================================================================
--- /dev/null
+++ llvm/include/llvm/Transforms/Utils/MisExpect.h
@@ -0,0 +1,43 @@
+//===--- MisExpect.cpp - Check Use of __builtin_expect() with PGO data ----===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// This contains code to emit warnings for potentially incorrect usage of
+// __builtin_expect(). This utility extracts the threshold values from metadata
+// associated with the instrumented Branch or Switch. The threshold values are
+// then used to determin if a warning would be emmited.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/LLVMContext.h"
+
+namespace llvm {
+namespace misexpect {
+
+/// verifyMisExpect - compares PGO counters to the thresholds used for
+/// __builtin_expect and warns if the PGO counters are outside of the expected
+/// range.
+/// \param I the Instruction being checked
+/// \param Weights A vector of profile weights for each target block
+/// \param Ctx The current LLVM context
+void verifyMisExpect(llvm::Instruction *I,
+                     const llvm::SmallVector<uint32_t, 4> &Weights,
+                     llvm::LLVMContext &Ctx);
+
+/// checkClangInstrumentation - verify if __builtin_expect matches PGO profile
+/// This function checks the frontend instrumentation in the backend when
+/// lowering __builtin_expect intrinsics. It checks for existing metadata, and
+/// then validates the use of builtin-expect against the assigned branch
+/// weights.
+/// \param I the Instruction being checked
+void checkClangInstrumentation(Instruction &I);
+
+} // namespace misexpect
+} // namespace llvm
Index: llvm/include/llvm/IR/MDBuilder.h
===================================================================
--- llvm/include/llvm/IR/MDBuilder.h
+++ llvm/include/llvm/IR/MDBuilder.h
@@ -16,6 +16,7 @@
 
 #include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/StringRef.h"
+#include "llvm/IR/Constants.h"
 #include "llvm/IR/GlobalValue.h"
 #include "llvm/Support/DataTypes.h"
 #include <utility>
@@ -75,6 +76,10 @@
   /// Return metadata containing the section prefix for a function.
   MDNode *createFunctionSectionPrefix(StringRef Prefix);
 
+  /// return metadata containing expected value
+  MDNode *createMisExpect(uint64_t Index, uint64_t LikelyWeight,
+                          uint64_t UnlikelyWeight);
+
   //===------------------------------------------------------------------===//
   // Range metadata.
   //===------------------------------------------------------------------===//
Index: llvm/include/llvm/IR/FixedMetadataKinds.def
===================================================================
--- llvm/include/llvm/IR/FixedMetadataKinds.def
+++ llvm/include/llvm/IR/FixedMetadataKinds.def
@@ -39,3 +39,4 @@
 LLVM_FIXED_MD_KIND(MD_access_group, "llvm.access.group", 25)
 LLVM_FIXED_MD_KIND(MD_callback, "callback", 26)
 LLVM_FIXED_MD_KIND(MD_preserve_access_index, "llvm.preserve.access.index", 27)
+LLVM_FIXED_MD_KIND(MD_misexpect, "misexpect", 28)
Index: llvm/include/llvm/IR/DiagnosticInfo.h
===================================================================
--- llvm/include/llvm/IR/DiagnosticInfo.h
+++ llvm/include/llvm/IR/DiagnosticInfo.h
@@ -75,7 +75,8 @@
   DK_MIRParser,
   DK_PGOProfile,
   DK_Unsupported,
-  DK_FirstPluginKind
+  DK_FirstPluginKind,
+  DK_MisExpect
 };
 
 /// Get the next available kind ID for a plugin diagnostic.
@@ -1002,6 +1003,31 @@
   void print(DiagnosticPrinter &DP) const override;
 };
 
+/// Diagnostic information for MisExpect analysis.
+class DiagnosticInfoMisExpect : public DiagnosticInfoWithLocationBase {
+public:
+  DiagnosticInfoMisExpect(const Function &Fn, const Twine &Msg,
+                          const DiagnosticLocation &Loc = DiagnosticLocation(),
+                          DiagnosticSeverity Severity = DS_Error)
+      : DiagnosticInfoWithLocationBase(DK_MisExpect, Severity, Fn, Loc),
+        Msg(Msg) {}
+
+  DiagnosticInfoMisExpect(const Instruction *Inst, Twine &Msg);
+
+  /// \see DiagnosticInfo::print.
+  void print(DiagnosticPrinter &DP) const override;
+
+  static bool classof(const DiagnosticInfo *DI) {
+    return DI->getKind() == DK_MisExpect;
+  }
+
+  const Twine &getMsg() const { return Msg; }
+
+private:
+  /// Message to report.
+  const Twine &Msg;
+};
+
 } // end namespace llvm
 
 #endif // LLVM_IR_DIAGNOSTICINFO_H
Index: clang/test/Profile/misexpect-switch.c
===================================================================
--- /dev/null
+++ clang/test/Profile/misexpect-switch.c
@@ -0,0 +1,41 @@
+// Test that misexpect detects mis-annotated switch statements
+
+// RUN: llvm-profdata merge %S/Inputs/misexpect-switch.proftext -o %t.profdata
+// RUN: %clang_cc1 %s -O2 -o - -emit-llvm -fprofile-instrument-use-path=%t.profdata -verify -Wmisexpect
+
+int sum(int *buff, int size);
+int random_sample(int *buff, int size);
+int rand();
+void init_arry();
+
+const int inner_loop = 1000;
+const int outer_loop = 20;
+const int arry_size = 25;
+
+int arry[arry_size] = {0};
+
+int main() {
+  init_arry();
+  int val = 0;
+
+  int j, k;
+  for (j = 0; j < outer_loop; ++j) {
+    for (k = 0; k < inner_loop; ++k) {
+      unsigned condition = rand() % 10000;
+      switch (__builtin_expect(condition, 0)) { // expected-warning-re {{Potential performance regression from use of __builtin_expect(): Annotation was correct on {{.+}}% of profiled executions.}}
+      case 0:
+        val += sum(arry, arry_size);
+        break;
+      case 1:
+      case 2:
+      case 3:
+        break;
+      default:
+        val += random_sample(arry, arry_size);
+        break;
+      } // end switch
+    }   // end inner_loop
+  }     // end outer_loop
+
+  return 0;
+}
Index: clang/test/Profile/misexpect-switch-only-default-case.c
===================================================================
--- /dev/null
+++ clang/test/Profile/misexpect-switch-only-default-case.c
@@ -0,0 +1,35 @@
+// Test that misexpect emits no warning when there is only one switch case
+
+// RUN: llvm-profdata merge %S/Inputs/misexpect-switch-default-only.proftext -o %t.profdata
+// RUN: %clang_cc1 %s -O2 -o - -disable-llvm-passes -emit-llvm -fprofile-instrument-use-path=%t.profdata -verify -fmisexpect
+
+// expected-no-diagnostics
+int sum(int *buff, int size);
+int random_sample(int *buff, int size);
+int rand();
+void init_arry();
+
+const int inner_loop = 1000;
+const int outer_loop = 20;
+const int arry_size = 25;
+
+int arry[arry_size] = {0};
+
+int main() {
+  init_arry();
+  int val = 0;
+
+  int j, k;
+  for (j = 0; j < outer_loop; ++j) {
+    for (k = 0; k < inner_loop; ++k) {
+      unsigned condition = rand() % 10000;
+      switch (__builtin_expect(condition, 0)) {
+      default:
+        val += random_sample(arry, arry_size);
+        break;
+      }; // end switch
+    }    // end inner_loop
+  }      // end outer_loop
+
+  return 0;
+}
Index: clang/test/Profile/misexpect-switch-nonconst.c
===================================================================
--- /dev/null
+++ clang/test/Profile/misexpect-switch-nonconst.c
@@ -0,0 +1,43 @@
+// Test that misexpect emits no warning when switch condition is non-const
+
+// RUN: llvm-profdata merge %S/Inputs/misexpect-switch.proftext -o %t.profdata
+// RUN: %clang_cc1 %s -O2 -o - -disable-llvm-passes -emit-llvm -fprofile-instrument-use-path=%t.profdata -verify -Wmisexpect
+
+// expected-no-diagnostics
+int sum(int *buff, int size);
+int random_sample(int *buff, int size);
+int rand();
+void init_arry();
+
+const int inner_loop = 1000;
+const int outer_loop = 20;
+const int arry_size = 25;
+
+int arry[arry_size] = {0};
+
+int main() {
+  init_arry();
+  int val = 0;
+
+  int j, k;
+  for (j = 0; j < outer_loop; ++j) {
+    for (k = 0; k < inner_loop; ++k) {
+      unsigned condition = rand() % 10000;
+      switch (__builtin_expect(condition, rand())) {
+      case 0:
+        val += sum(arry, arry_size);
+        break;
+      case 1:
+      case 2:
+      case 3:
+      case 4:
+        val += random_sample(arry, arry_size);
+        break;
+      default:
+        __builtin_unreachable();
+      } // end switch
+    }   // end inner_loop
+  }     // end outer_loop
+
+  return 0;
+}
Index: clang/test/Profile/misexpect-switch-default.c
===================================================================
--- /dev/null
+++ clang/test/Profile/misexpect-switch-default.c
@@ -0,0 +1,42 @@
+// Test that misexpect detects mis-annotated switch statements for default case
+
+// RUN: llvm-profdata merge %S/Inputs/misexpect-switch.proftext -o %t.profdata
+// RUN: %clang_cc1 %s -O2 -o - -disable-llvm-passes -emit-llvm -fprofile-instrument-use-path=%t.profdata -verify -Wmisexpect
+
+int sum(int *buff, int size);
+int random_sample(int *buff, int size);
+int rand();
+void init_arry();
+
+const int inner_loop = 1000;
+const int outer_loop = 20;
+const int arry_size = 25;
+
+int arry[arry_size] = {0};
+
+int main() {
+  init_arry();
+  int val = 0;
+
+  int j, k;
+  for (j = 0; j < outer_loop; ++j) {
+    for (k = 0; k < inner_loop; ++k) {
+      unsigned condition = rand() % 5;
+      switch (__builtin_expect(condition, 6)) { // expected-warning-re {{Potential performance regression from use of __builtin_expect(): Annotation was correct on {{.+}}% of profiled executions.}}
+      case 0:
+        val += sum(arry, arry_size);
+        break;
+      case 1:
+      case 2:
+      case 3:
+      case 4:
+        val += random_sample(arry, arry_size);
+        break;
+      default:
+        __builtin_unreachable();
+      } // end switch
+    }   // end inner_loop
+  }     // end outer_loop
+
+  return 0;
+}
Index: clang/test/Profile/misexpect-no-warning-without-flag.c
===================================================================
--- /dev/null
+++ clang/test/Profile/misexpect-no-warning-without-flag.c
@@ -0,0 +1,27 @@
+// Test that misexpect emits no warning without -fmisexpect flag
+
+// RUN: llvm-profdata merge %S/Inputs/misexpect-branch.proftext -o %t.profdata
+// RUN: %clang_cc1 %s -O2 -o - -disable-llvm-passes -emit-llvm -fprofile-instrument-use-path=%t.profdata -verify
+
+// expected-no-diagnostics
+#define likely(x) __builtin_expect(!!(x), 1)
+#define unlikely(x) __builtin_expect(!!(x), 0)
+
+int foo(int);
+int baz(int);
+int buzz();
+
+const int inner_loop = 100;
+const int outer_loop = 2000;
+
+int bar() {
+  int rando = buzz();
+  int x = 0;
+  if (likely(rando % (outer_loop * inner_loop) == 0)) {
+    x = baz(rando);
+  } else {
+    x = foo(50);
+  }
+  return x;
+}
+
Index: clang/test/Profile/misexpect-branch.c
===================================================================
--- /dev/null
+++ clang/test/Profile/misexpect-branch.c
@@ -0,0 +1,26 @@
+// Test that misexpect detects mis-annotated branches
+
+// RUN: llvm-profdata merge %S/Inputs/misexpect-branch.proftext -o %t.profdata
+// RUN: %clang_cc1 %s -O2 -o - -emit-llvm -fprofile-instrument-use-path=%t.profdata -verify -Wmisexpect
+
+#define likely(x) __builtin_expect(!!(x), 1)
+#define unlikely(x) __builtin_expect(!!(x), 0)
+
+int foo(int);
+int baz(int);
+int buzz();
+
+const int inner_loop = 100;
+const int outer_loop = 2000;
+
+int bar() {
+  int rando = buzz();
+  int x = 0;
+  if (likely(rando % (outer_loop * inner_loop) == 0)) { // expected-warning-re {{Potential performance regression from use of __builtin_expect(): Annotation was correct on {{.+}}% of profiled executions.}} expected-remark-re {{Potential performance regression from use of __builtin_expect(): Annotation was correct on {{.+}}% of profiled executions.}}
+    x = baz(rando);
+  } else {
+    x = foo(50);
+  }
+  return x;
+}
+
Index: clang/test/Profile/misexpect-branch-nonconst-expected-val.c
===================================================================
--- /dev/null
+++ clang/test/Profile/misexpect-branch-nonconst-expected-val.c
@@ -0,0 +1,26 @@
+// Test that misexpect emits no warning when condition is not a compile-time constant
+
+// RUN: llvm-profdata merge %S/Inputs/misexpect-branch-nonconst-expect-arg.proftext -o %t.profdata
+// RUN: %clang_cc1 %s -O2 -o - -disable-llvm-passes -emit-llvm -fprofile-instrument-use-path=%t.profdata -verify -Wmisexpect
+
+// expected-no-diagnostics
+#define likely(x) __builtin_expect(!!(x), 1)
+#define unlikely(x) __builtin_expect(!!(x), 0)
+
+int foo(int);
+int baz(int);
+int buzz();
+
+const int inner_loop = 100;
+const int outer_loop = 2000;
+
+int bar() {
+  int rando = buzz();
+  int x = 0;
+  if (__builtin_expect(rando % (outer_loop * inner_loop) == 0, buzz())) {
+    x = baz(rando);
+  } else {
+    x = foo(50);
+  }
+  return x;
+}
Index: clang/test/Profile/misexpect-branch-cold.c
===================================================================
--- /dev/null
+++ clang/test/Profile/misexpect-branch-cold.c
@@ -0,0 +1,27 @@
+// Test that misexpect emits no warning when prediction is correct
+
+// RUN: llvm-profdata merge %S/Inputs/misexpect-branch.proftext -o %t.profdata
+// RUN: %clang_cc1 %s -O2 -o - -disable-llvm-passes -emit-llvm -fprofile-instrument-use-path=%t.profdata -verify -Wmisexpect
+
+// expected-no-diagnostics
+#define likely(x) __builtin_expect(!!(x), 1)
+#define unlikely(x) __builtin_expect(!!(x), 0)
+
+int foo(int);
+int baz(int);
+int buzz();
+
+const int inner_loop = 100;
+const int outer_loop = 2000;
+
+int bar() {
+  int rando = buzz();
+  int x = 0;
+  if (unlikely(rando % (outer_loop * inner_loop) == 0)) {
+    x = baz(rando);
+  } else {
+    x = foo(50);
+  }
+  return x;
+}
+
Index: clang/test/Profile/Inputs/misexpect-switch.proftext
===================================================================
--- /dev/null
+++ clang/test/Profile/Inputs/misexpect-switch.proftext
@@ -0,0 +1,16 @@
+main
+# Func Hash:
+1965403898329309329
+# Num Counters:
+9
+# Counter Values:
+1
+20
+20000
+20000
+12
+26
+0
+0
+19962
+
Index: clang/test/Profile/Inputs/misexpect-switch-default-only.proftext
===================================================================
--- /dev/null
+++ clang/test/Profile/Inputs/misexpect-switch-default-only.proftext
@@ -0,0 +1,12 @@
+main
+# Func Hash:
+79676873694057560
+# Num Counters:
+5
+# Counter Values:
+1
+20
+20000
+20000
+20000
+
Index: clang/test/Profile/Inputs/misexpect-branch.proftext
===================================================================
--- /dev/null
+++ clang/test/Profile/Inputs/misexpect-branch.proftext
@@ -0,0 +1,9 @@
+bar
+# Func Hash:
+45795613684824
+# Num Counters:
+2
+# Counter Values:
+200000
+0
+
Index: clang/test/Profile/Inputs/misexpect-branch-nonconst-expect-arg.proftext
===================================================================
--- /dev/null
+++ clang/test/Profile/Inputs/misexpect-branch-nonconst-expect-arg.proftext
@@ -0,0 +1,9 @@
+bar
+# Func Hash:
+11262309464
+# Num Counters:
+2
+# Counter Values:
+200000
+2
+
Index: clang/lib/CodeGen/CodeGenFunction.cpp
===================================================================
--- clang/lib/CodeGen/CodeGenFunction.cpp
+++ clang/lib/CodeGen/CodeGenFunction.cpp
@@ -33,6 +33,7 @@
 #include "clang/Frontend/FrontendDiagnostic.h"
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/Dominators.h"
+#include "llvm/IR/Instructions.h"
 #include "llvm/IR/Intrinsics.h"
 #include "llvm/IR/MDBuilder.h"
 #include "llvm/IR/Operator.h"
@@ -1360,8 +1361,6 @@
   return true;
 }
 
-
-
 /// EmitBranchOnBoolExpr - Emit a branch on a boolean condition (e.g. for an if
 /// statement) to the specified blocks.  Based on the condition, this might try
 /// to simplify the codegen of the conditional based on the branch.
Index: clang/lib/CodeGen/CodeGenAction.cpp
===================================================================
--- clang/lib/CodeGen/CodeGenAction.cpp
+++ clang/lib/CodeGen/CodeGenAction.cpp
@@ -14,6 +14,7 @@
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/DeclCXX.h"
 #include "clang/AST/DeclGroup.h"
+#include "clang/Basic/DiagnosticFrontend.h"
 #include "clang/Basic/FileManager.h"
 #include "clang/Basic/LangStandard.h"
 #include "clang/Basic/SourceManager.h"
@@ -363,6 +364,7 @@
     bool StackSizeDiagHandler(const llvm::DiagnosticInfoStackSize &D);
     /// Specialized handler for unsupported backend feature diagnostic.
     void UnsupportedDiagHandler(const llvm::DiagnosticInfoUnsupported &D);
+    void MisExpectDiagHandler(const llvm::DiagnosticInfoMisExpect &D);
     /// Specialized handlers for optimization remarks.
     /// Note that these handlers only accept remarks and they always handle
     /// them.
@@ -615,6 +617,26 @@
         << Filename << Line << Column;
 }
 
+void BackendConsumer::MisExpectDiagHandler(
+    const llvm::DiagnosticInfoMisExpect &D) {
+  StringRef Filename;
+  unsigned Line, Column;
+  bool BadDebugInfo = false;
+  FullSourceLoc Loc =
+      getBestLocationFromDebugLoc(D, BadDebugInfo, Filename, Line, Column);
+
+  Diags.Report(Loc, diag::warn_profile_data_misexpect) << D.getMsg().str();
+  Diags.Report(Loc, diag::remark_profile_data_misexpect) << D.getMsg().str();
+
+  if (BadDebugInfo)
+    // If we were not able to translate the file:line:col information
+    // back to a SourceLocation, at least emit a note stating that
+    // we could not translate this location. This can happen in the
+    // case of #line directives.
+    Diags.Report(Loc, diag::note_fe_backend_invalid_loc)
+        << Filename << Line << Column;
+}
+
 void BackendConsumer::EmitOptimizationMessage(
     const llvm::DiagnosticInfoOptimizationBase &D, unsigned DiagID) {
   // We only support warnings and remarks.
@@ -785,6 +807,9 @@
   case llvm::DK_Unsupported:
     UnsupportedDiagHandler(cast<DiagnosticInfoUnsupported>(DI));
     return;
+  case llvm::DK_MisExpect:
+    MisExpectDiagHandler(cast<DiagnosticInfoMisExpect>(DI));
+    return;
   default:
     // Plugin IDs are not bound to any value as they are set dynamically.
     ComputeDiagRemarkID(Severity, backend_plugin, DiagID);
Index: clang/include/clang/Basic/DiagnosticGroups.td
===================================================================
--- clang/include/clang/Basic/DiagnosticGroups.td
+++ clang/include/clang/Basic/DiagnosticGroups.td
@@ -1031,6 +1031,7 @@
 def ProfileInstrMissing : DiagGroup<"profile-instr-missing">;
 def ProfileInstrOutOfDate : DiagGroup<"profile-instr-out-of-date">;
 def ProfileInstrUnprofiled : DiagGroup<"profile-instr-unprofiled">;
+def MisExpect : DiagGroup<"misexpect">;
 
 // AddressSanitizer frontend instrumentation remarks.
 def SanitizeAddressRemarks : DiagGroup<"sanitize-address">;
Index: clang/include/clang/Basic/DiagnosticFrontendKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticFrontendKinds.td
+++ clang/include/clang/Basic/DiagnosticFrontendKinds.td
@@ -275,6 +275,16 @@
 def warn_profile_data_unprofiled : Warning<
   "no profile data available for file \"%0\"">,
   InGroup<ProfileInstrUnprofiled>;
+def warn_profile_data_misexpect : Warning<
+  "Potential performance regression from use of __builtin_expect(): "
+  "Annotation was correct on %0 of profiled executions.">,
+  InGroup<MisExpect>,
+  DefaultIgnore;
+def remark_profile_data_misexpect : Remark<
+  "Potential performance regression from use of __builtin_expect(): "
+  "Annotation was correct on %0 of profiled executions.">,
+  BackendInfo,
+  InGroup<MisExpect>;
 
 } // end of instrumentation issue category
 
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