Index: llvm/include/llvm/Analysis/MemoryBuiltins.h
===================================================================
--- llvm/include/llvm/Analysis/MemoryBuiltins.h
+++ llvm/include/llvm/Analysis/MemoryBuiltins.h
@@ -250,7 +250,7 @@
 /// May create code to compute the result at run-time.
 class ObjectSizeOffsetEvaluator
   : public InstVisitor<ObjectSizeOffsetEvaluator, SizeOffsetEvalType> {
-  using BuilderTy = IRBuilder<TargetFolder>;
+  using BuilderTy = IRBuilder<TargetFolder, IRBuilderCallbackInserter>;
   using WeakEvalType = std::pair<WeakTrackingVH, WeakTrackingVH>;
   using CacheMapTy = DenseMap<const Value *, WeakEvalType>;
   using PtrSetTy = SmallPtrSet<const Value *, 8>;
@@ -264,6 +264,7 @@
   CacheMapTy CacheMap;
   PtrSetTy SeenVals;
   ObjectSizeOpts EvalOpts;
+  SmallPtrSet<Instruction *, 8> InsertedInstructions;
 
   SizeOffsetEvalType compute_(Value *V);
 
Index: llvm/lib/Analysis/MemoryBuiltins.cpp
===================================================================
--- llvm/lib/Analysis/MemoryBuiltins.cpp
+++ llvm/lib/Analysis/MemoryBuiltins.cpp
@@ -765,7 +765,10 @@
 ObjectSizeOffsetEvaluator::ObjectSizeOffsetEvaluator(
     const DataLayout &DL, const TargetLibraryInfo *TLI, LLVMContext &Context,
     ObjectSizeOpts EvalOpts)
-    : DL(DL), TLI(TLI), Context(Context), Builder(Context, TargetFolder(DL)),
+    : DL(DL), TLI(TLI), Context(Context),
+      Builder(Context, TargetFolder(DL),
+              IRBuilderCallbackInserter(
+                  [&](Instruction *I) { InsertedInstructions.insert(I); })),
       EvalOpts(EvalOpts) {
   // IntTy and Zero must be set for each compute() since the address space may
   // be different for later objects.
@@ -788,9 +791,16 @@
       if (CacheIt != CacheMap.end() && anyKnown(CacheIt->second))
         CacheMap.erase(CacheIt);
     }
+
+    // Erase any instructions we inserted as part of the traversal.
+    for (Instruction *I : InsertedInstructions) {
+      I->replaceAllUsesWith(UndefValue::get(I->getType()));
+      I->eraseFromParent();
+    }
   }
 
   SeenVals.clear();
+  InsertedInstructions.clear();
   return Result;
 }
 
@@ -934,24 +944,28 @@
     if (!bothKnown(EdgeData)) {
       OffsetPHI->replaceAllUsesWith(UndefValue::get(IntTy));
       OffsetPHI->eraseFromParent();
+      InsertedInstructions.erase(OffsetPHI);
       SizePHI->replaceAllUsesWith(UndefValue::get(IntTy));
       SizePHI->eraseFromParent();
+      InsertedInstructions.erase(SizePHI);
       return unknown();
     }
     SizePHI->addIncoming(EdgeData.first, PHI.getIncomingBlock(i));
     OffsetPHI->addIncoming(EdgeData.second, PHI.getIncomingBlock(i));
   }
 
-  Value *Size = SizePHI, *Offset = OffsetPHI, *Tmp;
-  if ((Tmp = SizePHI->hasConstantValue())) {
+  Value *Size = SizePHI, *Offset = OffsetPHI;
+  if (Value *Tmp = SizePHI->hasConstantValue()) {
     Size = Tmp;
     SizePHI->replaceAllUsesWith(Size);
     SizePHI->eraseFromParent();
+    InsertedInstructions.erase(SizePHI);
   }
-  if ((Tmp = OffsetPHI->hasConstantValue())) {
+  if (Value *Tmp = OffsetPHI->hasConstantValue()) {
     Offset = Tmp;
     OffsetPHI->replaceAllUsesWith(Offset);
     OffsetPHI->eraseFromParent();
+    InsertedInstructions.erase(OffsetPHI);
   }
   return std::make_pair(Size, Offset);
 }
Index: llvm/test/Instrumentation/BoundsChecking/phi.ll
===================================================================
--- llvm/test/Instrumentation/BoundsChecking/phi.ll
+++ llvm/test/Instrumentation/BoundsChecking/phi.ll
@@ -58,8 +58,6 @@
 ; CHECK: @f1_as1
 ; no checks are possible here
 ; CHECK-NOT: trap
-; CHECK: add i16 undef, -1
-; CHECK-NOT: trap
 entry:
   %0 = load i8, i8 addrspace(1)* %c, align 1
   %tobool1 = icmp eq i8 %0, 0
Index: llvm/test/Transforms/InstCombine/builtin-dynamic-object-size.ll
===================================================================
--- llvm/test/Transforms/InstCombine/builtin-dynamic-object-size.ll
+++ llvm/test/Transforms/InstCombine/builtin-dynamic-object-size.ll
@@ -71,6 +71,40 @@
 
 ; CHECK: ret i64 0
 
+@d = common global i8 0, align 1
+@c = common global i32 0, align 4
+
+; Function Attrs: nounwind
+define void @f() {
+entry:
+  %.pr = load i32, i32* @c, align 4
+  %tobool4 = icmp eq i32 %.pr, 0
+  br i1 %tobool4, label %for.end, label %for.body
+
+for.body:                                         ; preds = %entry, %for.body
+  %dp.05 = phi i8* [ %add.ptr, %for.body ], [ @d, %entry ]
+  %0 = tail call i64 @llvm.objectsize.i64.p0i8(i8* %dp.05, i1 false, i1 true, i1 true)
+  %conv = trunc i64 %0 to i32
+  tail call void @bury(i32 %conv) #3
+  %1 = load i32, i32* @c, align 4
+  %idx.ext = sext i32 %1 to i64
+  %add.ptr.offs = add i64 %idx.ext, 0
+  %2 = add i64 undef, %add.ptr.offs
+  %add.ptr = getelementptr inbounds i8, i8* %dp.05, i64 %idx.ext
+  %add = shl nsw i32 %1, 1
+  store i32 %add, i32* @c, align 4
+  %tobool = icmp eq i32 %1, 0
+  br i1 %tobool, label %for.end, label %for.body
+
+for.end:                                          ; preds = %for.body, %entry
+  ret void
+}
+
+; CHECK:   define void @f()
+; CHECK:     call i64 @llvm.objectsize.i64.p0i8(
+
+declare void @bury(i32) local_unnamed_addr #2
+
 ; Function Attrs: nounwind allocsize(0)
 declare i8* @malloc(i64)