Revert "[InstrProfiling] Emit bias variable eagerly"

This reverts commit 6660cec since
it was superseded by https://reviews.llvm.org/D98061.

Author: petrhosek

llvm/include/llvm/Transforms/Instrumentation/InstrProfiling.h

@@ -121,9 +121,6 @@ class InstrProfiling : public PassInfoMixin<InstrProfiling> {
   /// Create a static initializer for our data, on platforms that need it,
   /// and for any profile output file that was specified.
   void emitInitialization();
-
-  // Emit the variable used for runtime counter relocation.
-  bool emitBiasVar();
 };
 
 } // end namespace llvm

llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp

@@ -551,10 +551,6 @@ bool InstrProfiling::run(
   // Emit the runtime hook even if no counters are present.
   bool MadeChange = emitRuntimeHook();
 
-  // Emit the bias variable in each module when counter relocation is enabled.
-  if (isRuntimeCounterRelocationEnabled())
-    MadeChange |= emitBiasVar();
-
   // Improve compile time by avoiding linear scans when there is no work.
   GlobalVariable *CoverageNamesVar =
       M.getNamedGlobal(getCoverageUnusedNamesVarName());
@@ -697,6 +693,21 @@ void InstrProfiling::lowerIncrement(InstrProfIncrementInst *Inc) {
     if (!LI) {
       IRBuilder<> Builder(&I);
       GlobalVariable *Bias = M->getGlobalVariable(getInstrProfCounterBiasVarName());
+      if (!Bias) {
+        // Compiler must define this variable when runtime counter relocation
+        // is being used. Runtime has a weak external reference that is used
+        // to check whether that's the case or not.
+        Bias = new GlobalVariable(*M, Int64Ty, false, GlobalValue::LinkOnceODRLinkage,
+                                  Constant::getNullValue(Int64Ty),
+                                  getInstrProfCounterBiasVarName());
+        Bias->setVisibility(GlobalVariable::HiddenVisibility);
+        // A definition that's weak (linkonce_odr) without being in a COMDAT
+        // section wouldn't lead to link errors, but it would lead to a dead
+        // data word from every TU but one. Putting it in COMDAT ensures there
+        // will be exactly one data slot in the link.
+        if (TT.supportsCOMDAT())
+          Bias->setComdat(M->getOrInsertComdat(Bias->getName()));
+      }
       LI = Builder.CreateLoad(Int64Ty, Bias);
     }
     auto *Add = Builder.CreateAdd(Builder.CreatePtrToInt(Addr, Int64Ty), LI);
@@ -1183,26 +1194,3 @@ void InstrProfiling::emitInitialization() {
 
   appendToGlobalCtors(*M, F, 0);
 }
-
-bool InstrProfiling::emitBiasVar() {
-  // Module already provided its own variable, nothin to do.
-  if (M->getGlobalVariable(getInstrProfCounterBiasVarName()))
-    return false;
-
-  // Compiler must define this variable when runtime counter relocation
-  // is being used. Runtime has a weak external reference that is used
-  // to check whether that's the case or not.
-  Type *Int64Ty = Type::getInt64Ty(M->getContext());
-  auto *Bias = new GlobalVariable(*M, Int64Ty, false, GlobalValue::LinkOnceODRLinkage,
-                            Constant::getNullValue(Int64Ty),
-                            getInstrProfCounterBiasVarName());
-  Bias->setVisibility(GlobalVariable::HiddenVisibility);
-  // A definition that's weak (linkonce_odr) without being in a COMDAT
-  // section wouldn't lead to link errors, but it would lead to a dead
-  // data word from every TU but one. Putting it in COMDAT ensures there
-  // will be exactly one data slot in the link.
-  if (TT.supportsCOMDAT())
-    Bias->setComdat(M->getOrInsertComdat(Bias->getName()));
-
-  return true;
-}