diff --git a/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp b/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
index 79947ff892a1..73e7867d0a34 100644
--- a/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
+++ b/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
@@ -715,6 +715,7 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
   ValueMap<Value*, Value*> ShadowMap, OriginMap;
   std::unique_ptr<VarArgHelper> VAHelper;
   const TargetLibraryInfo *TLI;
+  BasicBlock *ActualFnStart;
 
   // The following flags disable parts of MSan instrumentation based on
   // blacklist contents and command-line options.
@@ -747,6 +748,9 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
     CheckReturnValue = SanitizeFunction && (F.getName() == "main");
     TLI = &MS.getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
 
+    MS.initializeCallbacks(*F.getParent());
+    ActualFnStart = &F.getEntryBlock();
+
     DEBUG(if (!InsertChecks)
           dbgs() << "MemorySanitizer is not inserting checks into '"
                  << F.getName() << "'\n");
@@ -931,8 +935,6 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
 
   /// \brief Add MemorySanitizer instrumentation to a function.
   bool runOnFunction() {
-    MS.initializeCallbacks(*F.getParent());
-
     // In the presence of unreachable blocks, we may see Phi nodes with
     // incoming nodes from such blocks. Since InstVisitor skips unreachable
     // blocks, such nodes will not have any shadow value associated with them.
@@ -942,7 +944,7 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
     // Iterate all BBs in depth-first order and create shadow instructions
     // for all instructions (where applicable).
     // For PHI nodes we create dummy shadow PHIs which will be finalized later.
-    for (BasicBlock *BB : depth_first(&F.getEntryBlock()))
+    for (BasicBlock *BB : depth_first(ActualFnStart))
       visit(*BB);
 
     // Finalize PHI nodes.
@@ -1216,7 +1218,7 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
       if (*ShadowPtr)
         return *ShadowPtr;
       Function *F = A->getParent();
-      IRBuilder<> EntryIRB(F->getEntryBlock().getFirstNonPHI());
+      IRBuilder<> EntryIRB(ActualFnStart->getFirstNonPHI());
       unsigned ArgOffset = 0;
       const DataLayout &DL = F->getParent()->getDataLayout();
       for (auto &FArg : F->args()) {
@@ -3214,7 +3216,7 @@ struct VarArgAMD64Helper : public VarArgHelper {
     if (!VAStartInstrumentationList.empty()) {
       // If there is a va_start in this function, make a backup copy of
       // va_arg_tls somewhere in the function entry block.
-      IRBuilder<> IRB(F.getEntryBlock().getFirstNonPHI());
+      IRBuilder<> IRB(MSV.ActualFnStart->getFirstNonPHI());
       VAArgOverflowSize = IRB.CreateLoad(MS.VAArgOverflowSizeTLS);
       Value *CopySize =
         IRB.CreateAdd(ConstantInt::get(MS.IntptrTy, AMD64FpEndOffset),
@@ -3336,7 +3338,7 @@ struct VarArgMIPS64Helper : public VarArgHelper {
   void finalizeInstrumentation() override {
     assert(!VAArgSize && !VAArgTLSCopy &&
            "finalizeInstrumentation called twice");
-    IRBuilder<> IRB(F.getEntryBlock().getFirstNonPHI());
+    IRBuilder<> IRB(MSV.ActualFnStart->getFirstNonPHI());
     VAArgSize = IRB.CreateLoad(MS.VAArgOverflowSizeTLS);
     Value *CopySize = IRB.CreateAdd(ConstantInt::get(MS.IntptrTy, 0),
                                     VAArgSize);
@@ -3521,7 +3523,7 @@ struct VarArgAArch64Helper : public VarArgHelper {
     if (!VAStartInstrumentationList.empty()) {
       // If there is a va_start in this function, make a backup copy of
       // va_arg_tls somewhere in the function entry block.
-      IRBuilder<> IRB(F.getEntryBlock().getFirstNonPHI());
+      IRBuilder<> IRB(MSV.ActualFnStart->getFirstNonPHI());
       VAArgOverflowSize = IRB.CreateLoad(MS.VAArgOverflowSizeTLS);
       Value *CopySize =
         IRB.CreateAdd(ConstantInt::get(MS.IntptrTy, AArch64VAEndOffset),
@@ -3757,7 +3759,7 @@ struct VarArgPowerPC64Helper : public VarArgHelper {
   void finalizeInstrumentation() override {
     assert(!VAArgSize && !VAArgTLSCopy &&
            "finalizeInstrumentation called twice");
-    IRBuilder<> IRB(F.getEntryBlock().getFirstNonPHI());
+    IRBuilder<> IRB(MSV.ActualFnStart->getFirstNonPHI());
     VAArgSize = IRB.CreateLoad(MS.VAArgOverflowSizeTLS);
     Value *CopySize = IRB.CreateAdd(ConstantInt::get(MS.IntptrTy, 0),
                                     VAArgSize);