[PGO] Simplify coverage mapping lowering

Coverage mapping data may reference names of functions
that are skipped by FE (e.g, unused inline functions). Since
those functions are skipped, normal instr-prof function lowering
pass won't put those names in the right section, so special 
handling is needed to walk through coverage mapping structure
and recollect the references.

With this patch, only names that are skipped are processed. This
simplifies the lowering code and it no longer needs to make 
assumptions coverage mapping data layout. It should also be 
more efficient.

llvm-svn: 257092

3 files changed, 21 insertions, 5 deletions

diff --git a/clang/lib/CodeGen/CodeGenPGO.cpp b/clang/lib/CodeGen/CodeGenPGO.cpp
index 5ae861eab0d3..2c0d93b394ac 100644
--- a/clang/lib/CodeGen/CodeGenPGO.cpp
+++ b/clang/lib/CodeGen/CodeGenPGO.cpp
@@ -699,7 +699,7 @@ CodeGenPGO::emitEmptyCounterMapping(const Decl *D, StringRef Name,
 
   setFuncName(Name, Linkage);
   CGM.getCoverageMapping()->addFunctionMappingRecord(
-      FuncNameVar, FuncName, FunctionHash, CoverageMapping);
+      FuncNameVar, FuncName, FunctionHash, CoverageMapping, false);
 }
 
 void CodeGenPGO::computeRegionCounts(const Decl *D) {
diff --git a/clang/lib/CodeGen/CoverageMappingGen.cpp b/clang/lib/CodeGen/CoverageMappingGen.cpp
index 1d4d7099e194..03e22cd398aa 100644
--- a/clang/lib/CodeGen/CoverageMappingGen.cpp
+++ b/clang/lib/CodeGen/CoverageMappingGen.cpp
@@ -910,11 +910,11 @@ static void dump(llvm::raw_ostream &OS, StringRef FunctionName,
 }
 
 void CoverageMappingModuleGen::addFunctionMappingRecord(
-    llvm::GlobalVariable *NamePtr, StringRef NameValue,
-    uint64_t FuncHash, const std::string &CoverageMapping) {
+    llvm::GlobalVariable *NamePtr, StringRef NameValue, uint64_t FuncHash,
+    const std::string &CoverageMapping, bool isUsed) {
   llvm::LLVMContext &Ctx = CGM.getLLVMContext();
   if (!FunctionRecordTy) {
-    #define COVMAP_FUNC_RECORD(Type, LLVMType, Name, Init) LLVMType,
+#define COVMAP_FUNC_RECORD(Type, LLVMType, Name, Init) LLVMType,
     llvm::Type *FunctionRecordTypes[] = {
       #include "llvm/ProfileData/InstrProfData.inc"
     };
@@ -929,6 +929,9 @@ void CoverageMappingModuleGen::addFunctionMappingRecord(
   };
   FunctionRecords.push_back(llvm::ConstantStruct::get(
       FunctionRecordTy, makeArrayRef(FunctionRecordVals)));
+  if (!isUsed)
+    FunctionNames.push_back(
+        llvm::ConstantExpr::getBitCast(NamePtr, llvm::Type::getInt8PtrTy(Ctx)));
   CoverageMappings += CoverageMapping;
 
   if (CGM.getCodeGenOpts().DumpCoverageMapping) {
@@ -1023,6 +1026,17 @@ void CoverageMappingModuleGen::emit() {
 
   // Make sure the data doesn't get deleted.
   CGM.addUsedGlobal(CovData);
+  // Create the deferred function records array
+  if (!FunctionNames.empty()) {
+    auto NamesArrTy = llvm::ArrayType::get(llvm::Type::getInt8PtrTy(Ctx),
+                                           FunctionNames.size());
+    auto NamesArrVal = llvm::ConstantArray::get(NamesArrTy, FunctionNames);
+    // This variable will *NOT* be emitted to the object file. It is used
+    // to pass the list of names referenced to codegen.
+    new llvm::GlobalVariable(CGM.getModule(), NamesArrTy, true,
+                             llvm::GlobalValue::InternalLinkage, NamesArrVal,
+                             llvm::getCoverageNamesVarName());
+  }
 }
 
 unsigned CoverageMappingModuleGen::getFileID(const FileEntry *File) {
diff --git a/clang/lib/CodeGen/CoverageMappingGen.h b/clang/lib/CodeGen/CoverageMappingGen.h
index 0d1bf6d975c9..9ae2bcffe4ca 100644
--- a/clang/lib/CodeGen/CoverageMappingGen.h
+++ b/clang/lib/CodeGen/CoverageMappingGen.h
@@ -54,6 +54,7 @@ class CoverageMappingModuleGen {
   CoverageSourceInfo &SourceInfo;
   llvm::SmallDenseMap<const FileEntry *, unsigned, 8> FileEntries;
   std::vector<llvm::Constant *> FunctionRecords;
+  std::vector<llvm::Constant *> FunctionNames;
   llvm::StructType *FunctionRecordTy;
   std::string CoverageMappings;
 
@@ -70,7 +71,8 @@ public:
   void addFunctionMappingRecord(llvm::GlobalVariable *FunctionName,
                                 StringRef FunctionNameValue,
                                 uint64_t FunctionHash,
-                                const std::string &CoverageMapping);
+                                const std::string &CoverageMapping,
+                                bool isUsed = true);
 
   /// \brief Emit the coverage mapping data for a translation unit.
   void emit();