[InstrProfiling] Don't generate __llvm_profile_runtime_user

This is no longer needed, we can add __llvm_profile_runtime directly
to llvm.compiler.used or llvm.used to achieve the same effect.

Differential Revision: https://reviews.llvm.org/D98325

Author: petrhosek

llvm/include/llvm/ProfileData/InstrProf.h

@@ -149,12 +149,6 @@ inline StringRef getInstrProfRuntimeHookVarName() {
   return INSTR_PROF_QUOTE(INSTR_PROF_PROFILE_RUNTIME_VAR);
 }
 
-/// Return the name of the compiler generated function that references the
-/// runtime hook variable. The function is a weak global.
-inline StringRef getInstrProfRuntimeHookVarUseFuncName() {
-  return "__llvm_profile_runtime_user";
-}
-
 inline StringRef getInstrProfCounterBiasVarName() {
   return "__llvm_profile_counter_bias";
 }

llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp

@@ -1073,23 +1073,8 @@ bool InstrProfiling::emitRuntimeHook() {
       new GlobalVariable(*M, Int32Ty, false, GlobalValue::ExternalLinkage,
                          nullptr, getInstrProfRuntimeHookVarName());
 
-  // Make a function that uses it.
-  auto *User = Function::Create(FunctionType::get(Int32Ty, false),
-                                GlobalValue::LinkOnceODRLinkage,
-                                getInstrProfRuntimeHookVarUseFuncName(), M);
-  User->addFnAttr(Attribute::NoInline);
-  if (Options.NoRedZone)
-    User->addFnAttr(Attribute::NoRedZone);
-  User->setVisibility(GlobalValue::HiddenVisibility);
-  if (TT.supportsCOMDAT())
-    User->setComdat(M->getOrInsertComdat(User->getName()));
-
-  IRBuilder<> IRB(BasicBlock::Create(M->getContext(), "", User));
-  auto *Load = IRB.CreateLoad(Int32Ty, Var);
-  IRB.CreateRet(Load);
-
   // Mark the user variable as used so that it isn't stripped out.
-  CompilerUsedVars.push_back(User);
+  CompilerUsedVars.push_back(Var);
   return true;
 }
 

llvm/test/Instrumentation/InstrProfiling/linkage.ll

@@ -81,11 +81,3 @@ define available_externally void @foo_extern() {
 }
 
 declare void @llvm.instrprof.increment(i8*, i64, i32, i32)
-
-; MACHO: define linkonce_odr hidden i32 @__llvm_profile_runtime_user() {{.*}} {
-; MACHO:   %[[REG:.*]] = load i32, i32* @__llvm_profile_runtime
-; MACHO:   ret i32 %[[REG]]
-; MACHO: }
-; COFF: define linkonce_odr hidden i32 @__llvm_profile_runtime_user() {{.*}} comdat {
-; ELF-NOT: define linkonce_odr hidden i32 @__llvm_profile_runtime_user() {{.*}} {
-; ELF-NOT:   %[[REG:.*]] = load i32, i32* @__llvm_profile_runtime

llvm/test/Instrumentation/InstrProfiling/profiling.ll

@@ -54,11 +54,12 @@ define void @baz() {
 
 declare void @llvm.instrprof.increment(i8*, i64, i32, i32)
 
-; ELF:   @llvm.compiler.used = appending global {{.*}} @__llvm_profile_runtime_user {{.*}} @__profd_foo {{.*}} @__profd_bar {{.*}} @__profd_baz
-; MACHO: @llvm.used = appending global {{.*}} @__llvm_profile_runtime_user {{.*}} @__profd_foo {{.*}} @__profd_bar {{.*}} @__profd_baz
-; WIN:   @llvm.used = appending global {{.*}} @__llvm_profile_runtime_user {{.*}} @__profd_foo {{.*}} @__profd_bar {{.*}} @__profd_baz
+; ELF:   @llvm.compiler.used = appending global {{.*}} @__llvm_profile_runtime {{.*}} @__profd_foo {{.*}} @__profd_bar {{.*}} @__profd_baz
+; MACHO: @llvm.used = appending global {{.*}} @__llvm_profile_runtime {{.*}} @__profd_foo {{.*}} @__profd_bar {{.*}} @__profd_baz
+; WIN:   @llvm.used = appending global {{.*}} @__llvm_profile_runtime {{.*}} @__profd_foo {{.*}} @__profd_bar {{.*}} @__profd_baz
 
 ; ELF_GENERIC:      define internal void @__llvm_profile_register_functions() unnamed_addr {
+; ELF_GENERIC-NEXT:   call void @__llvm_profile_register_function(i8* bitcast (i32* @__llvm_profile_runtime to i8*))
 ; ELF_GENERIC-NEXT:   call void @__llvm_profile_register_function(i8* bitcast ({ i64, i64, i64*, i8*, i8*, i32, [2 x i16] }* @__profd_foo to i8*))
 ; ELF_GENERIC-NEXT:   call void @__llvm_profile_register_function(i8* bitcast ({ i64, i64, i64*, i8*, i8*, i32, [2 x i16] }* @__profd_bar to i8*))
 ; ELF_GENERIC-NEXT:   call void @__llvm_profile_register_function(i8* bitcast ({ i64, i64, i64*, i8*, i8*, i32, [2 x i16] }* @__profd_baz to i8*))