diff --git a/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp b/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
--- a/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
+++ b/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
@@ -2507,6 +2507,12 @@
   void visitAShr(BinaryOperator &I) { handleShift(I); }
   void visitLShr(BinaryOperator &I) { handleShift(I); }
 
+  void replaceInst(Instruction *Old, Instruction *New) {
+    if (Old == ActualFnStart)
+      ActualFnStart = New;
+    Old->eraseFromParent();
+  }
+
   /// Instrument llvm.memmove
   ///
   /// At this point we don't know if llvm.memmove will be inlined or not.
@@ -2519,12 +2525,12 @@
   /// Similar situation exists for memcpy and memset.
   void visitMemMoveInst(MemMoveInst &I) {
     IRBuilder<> IRB(&I);
-    IRB.CreateCall(
+    Instruction *NewInst = IRB.CreateCall(
         MS.MemmoveFn,
         {IRB.CreatePointerCast(I.getArgOperand(0), IRB.getInt8PtrTy()),
          IRB.CreatePointerCast(I.getArgOperand(1), IRB.getInt8PtrTy()),
          IRB.CreateIntCast(I.getArgOperand(2), MS.IntptrTy, false)});
-    I.eraseFromParent();
+    replaceInst(&I, NewInst);
   }
 
   // Similar to memmove: avoid copying shadow twice.
@@ -2533,23 +2539,23 @@
   // alignment.
   void visitMemCpyInst(MemCpyInst &I) {
     IRBuilder<> IRB(&I);
-    IRB.CreateCall(
+    Instruction *NewInst = IRB.CreateCall(
         MS.MemcpyFn,
         {IRB.CreatePointerCast(I.getArgOperand(0), IRB.getInt8PtrTy()),
          IRB.CreatePointerCast(I.getArgOperand(1), IRB.getInt8PtrTy()),
          IRB.CreateIntCast(I.getArgOperand(2), MS.IntptrTy, false)});
-    I.eraseFromParent();
+    replaceInst(&I, NewInst);
   }
 
   // Same as memcpy.
   void visitMemSetInst(MemSetInst &I) {
     IRBuilder<> IRB(&I);
-    IRB.CreateCall(
+    Instruction *NewInst = IRB.CreateCall(
         MS.MemsetFn,
         {IRB.CreatePointerCast(I.getArgOperand(0), IRB.getInt8PtrTy()),
          IRB.CreateIntCast(I.getArgOperand(1), IRB.getInt32Ty(), false),
          IRB.CreateIntCast(I.getArgOperand(2), MS.IntptrTy, false)});
-    I.eraseFromParent();
+    replaceInst(&I, NewInst);
   }
 
   void visitVAStartInst(VAStartInst &I) {