[Coverage] Drop records for functions DCE'd after builtin lowering

include/swift/SIL/SILCoverageMap.h

@@ -73,9 +73,6 @@ class SILCoverageMap : public llvm::ilist_node<SILCoverageMap>,
   // Tail-allocated expression list.
   MutableArrayRef<llvm::coverage::CounterExpression> Expressions;
 
-  // Whether the coverage mapping's name data is in the profile symbol table.
-  bool HasSymtabEntry;
-
   // Disallow copying into temporary objects.
   SILCoverageMap(const SILCoverageMap &other) = delete;
   SILCoverageMap &operator=(const SILCoverageMap &) = delete;
@@ -112,14 +109,6 @@ class SILCoverageMap : public llvm::ilist_node<SILCoverageMap>,
     return Expressions;
   }
 
-  /// Check whether this coverage mapping can reference its name data within
-  /// the profile symbol table.
-  bool hasSymtabEntry() const { return HasSymtabEntry; }
-
-  /// Guarantee that this coverage mapping can reference its name data within
-  /// the profile symbol table.
-  void setSymtabEntryGuaranteed() { HasSymtabEntry = true; }
-
   void printCounter(llvm::raw_ostream &OS, llvm::coverage::Counter C) const;
 
   /// Print the coverage map.

lib/IRGen/GenBuiltin.cpp

@@ -256,15 +256,6 @@ void irgen::emitBuiltinCall(IRGenFunction &IGF, const BuiltinInfo &Builtin,
     replacement.add(NameGEP);
     replacement.add(args.claimAll());
     args = std::move(replacement);
-
-    if (Opts.EmitProfileCoverageMapping) {
-      // Update the associated coverage mapping: it's now safe to emit, because
-      // a symtab entry for this function is guaranteed (r://39146527).
-      auto &coverageMaps = SILMod.getCoverageMaps();
-      auto CovMapIt = coverageMaps.find(PGOFuncName);
-      if (CovMapIt != coverageMaps.end())
-        CovMapIt->second->setSymtabEntryGuaranteed();
-    }
   }
 
   if (IID != llvm::Intrinsic::not_intrinsic) {

lib/IRGen/GenCoverage.cpp

@@ -39,9 +39,17 @@ static std::string getCoverageSection(IRGenModule &IGM) {
 
 void IRGenModule::emitCoverageMapping() {
   std::vector<const SILCoverageMap *> Mappings;
-  for (const auto &M : getSILModule().getCoverageMaps())
-    if (M.second->hasSymtabEntry())
-      Mappings.push_back(M.second);
+  for (const auto &M : getSILModule().getCoverageMaps()) {
+    // Check whether this coverage mapping can reference its name data within
+    // the profile symbol table. If the name global is gone, this function has
+    // been optimized out.
+    StringRef PGOFuncName = M.second->getPGOFuncName();
+    std::string PGOFuncNameVar = llvm::getPGOFuncNameVarName(
+        PGOFuncName, llvm::GlobalValue::LinkOnceAnyLinkage);
+    if (!Module.getNamedGlobal(PGOFuncNameVar))
+      continue;
+    Mappings.push_back(M.second);
+  }
 
   // If there aren't any coverage maps, there's nothing to emit.
   if (Mappings.empty())
@@ -106,6 +114,7 @@ void IRGenModule::emitCoverageMapping() {
     StringRef CoverageMapping(OS.str().c_str() + PrevSize, MappingLen);
 
     StringRef NameValue = M->getPGOFuncName();
+    assert(!NameValue.empty() && "Expected a named record");
     uint64_t FuncHash = M->getHash();
 
     // Create a record for this function.

lib/SIL/SILCoverageMap.cpp

@@ -50,8 +50,7 @@ SILCoverageMap::create(SILModule &M, StringRef Filename, StringRef Name,
   return CM;
 }
 
-SILCoverageMap::SILCoverageMap(uint64_t Hash)
-    : Hash(Hash), HasSymtabEntry(false) {}
+SILCoverageMap::SILCoverageMap(uint64_t Hash) : Hash(Hash) {}
 
 SILCoverageMap::~SILCoverageMap() {}
 

lib/SIL/SILProfiler.cpp

@@ -1079,6 +1079,9 @@ void SILProfiler::assignRegionCounters() {
       CurrentFuncName, getEquivalentPGOLinkage(CurrentFuncLinkage),
       CurrentFileName);
 
+  assert((!CurrentFuncName.empty() && !PGOFuncName.empty()) &&
+         "Expected covered region to be named");
+
   LLVM_DEBUG(llvm::dbgs() << "Assigning counters to: " << CurrentFuncName
                           << "\n");
   Root.walk(Mapper);

test/Profiler/coverage_dead_code_elim.swift

@@ -0,0 +1,5 @@
+// RUN: %target-swift-frontend %s -profile-generate -profile-coverage-mapping  -O -whole-module-optimization -emit-ir -o - | %FileCheck %s
+
+// CHECK-NOT: llvm_coverage_mapping = internal constant
+
+func foo() {}