3 files changed, 32 insertions, 15 deletions

diff --git a/clang/lib/CodeGen/CodeGenPGO.cpp b/clang/lib/CodeGen/CodeGenPGO.cpp
index 7b45650572a..ef490ff6799 100644
--- a/clang/lib/CodeGen/CodeGenPGO.cpp
+++ b/clang/lib/CodeGen/CodeGenPGO.cpp
@@ -814,6 +814,35 @@ namespace {
   };
 }
 
+static void emitRuntimeHook(CodeGenModule &CGM) {
+  constexpr const char *RuntimeVarName = "__llvm_profile_runtime";
+  constexpr const char *RuntimeUserName = "__llvm_profile_runtime_user";
+  if (CGM.getModule().getGlobalVariable(RuntimeVarName))
+    return;
+
+  // Declare the runtime hook.
+  llvm::LLVMContext &Ctx = CGM.getLLVMContext();
+  auto *Int32Ty = llvm::Type::getInt32Ty(Ctx);
+  auto *Var = new llvm::GlobalVariable(CGM.getModule(), Int32Ty, false,
+                                       llvm::GlobalValue::ExternalLinkage,
+                                       nullptr, RuntimeVarName);
+
+  // Make a function that uses it.
+  auto *User = llvm::Function::Create(llvm::FunctionType::get(Int32Ty, false),
+                                      llvm::GlobalValue::LinkOnceODRLinkage,
+                                      RuntimeUserName, &CGM.getModule());
+  User->addFnAttr(llvm::Attribute::NoInline);
+  if (CGM.getCodeGenOpts().DisableRedZone)
+    User->addFnAttr(llvm::Attribute::NoRedZone);
+  CGBuilderTy Builder(llvm::BasicBlock::Create(CGM.getLLVMContext(), "", User));
+  auto *Load = Builder.CreateLoad(Var);
+  Builder.CreateRet(Load);
+
+  // Create a use of the function.  Now the definition of the runtime variable
+  // should get pulled in, along with any static initializears.
+  CGM.addUsedGlobal(User);
+}
+
 void CodeGenPGO::assignRegionCounters(const Decl *D, llvm::Function *Fn) {
   bool InstrumentRegions = CGM.getCodeGenOpts().ProfileInstrGenerate;
   PGOProfileData *PGOData = CGM.getPGOData();
@@ -839,8 +868,10 @@ void CodeGenPGO::assignRegionCounters(const Decl *D, llvm::Function *Fn) {
   }
 
   mapRegionCounters(D);
-  if (InstrumentRegions)
+  if (InstrumentRegions) {
+    emitRuntimeHook(CGM);
     emitCounterVariables();
+  }
   if (PGOData) {
     loadRegionCounts(PGOData);
     computeRegionCounts(D);
diff --git a/clang/lib/Driver/ToolChains.cpp b/clang/lib/Driver/ToolChains.cpp
index b348d6c24d6..4bb8332ea7d 100644
--- a/clang/lib/Driver/ToolChains.cpp
+++ b/clang/lib/Driver/ToolChains.cpp
@@ -325,13 +325,6 @@ void DarwinClang::AddLinkRuntimeLibArgs(const ArgList &Args,
       Args.hasArg(options::OPT_fprofile_instr_generate) ||
       Args.hasArg(options::OPT_fcreate_profile) ||
       Args.hasArg(options::OPT_coverage)) {
-    // Pull in runtime for -fprofile-inst-generate.  This is required since
-    // there are no calls to the runtime in the code.
-    if (Args.hasArg(options::OPT_fprofile_instr_generate)) {
-      CmdArgs.push_back("-u");
-      CmdArgs.push_back("___llvm_profile_runtime");
-    }
-
     // Select the appropriate runtime library for the target.
     if (isTargetIOSBased())
       AddLinkRuntimeLib(Args, CmdArgs, "libclang_rt.profile_ios.a");
diff --git a/clang/lib/Driver/Tools.cpp b/clang/lib/Driver/Tools.cpp
index 2141cc9656b..9a31eb9f9d6 100644
--- a/clang/lib/Driver/Tools.cpp
+++ b/clang/lib/Driver/Tools.cpp
@@ -1817,13 +1817,6 @@ static void addProfileRT(
         Args.hasArg(options::OPT_coverage)))
     return;
 
-  // Pull in runtime for -fprofile-inst-generate.  This is required since there
-  // are no calls to the runtime in the code.
-  if (Args.hasArg(options::OPT_fprofile_instr_generate)) {
-    CmdArgs.push_back("-u");
-    CmdArgs.push_back("___llvm_profile_runtime");
-  }
-
   SmallString<128> LibProfile = getCompilerRTLibDir(TC);
   llvm::sys::path::append(LibProfile,
       Twine("libclang_rt.profile-") + getArchNameForCompilerRTLib(TC) + ".a");