diff --git a/llvm/lib/Transforms/IPO/LowerTypeTests.cpp b/llvm/lib/Transforms/IPO/LowerTypeTests.cpp
--- a/llvm/lib/Transforms/IPO/LowerTypeTests.cpp
+++ b/llvm/lib/Transforms/IPO/LowerTypeTests.cpp
@@ -117,6 +117,11 @@
     cl::desc("Write summary to given YAML file after running pass"),
     cl::Hidden);
 
+static cl::opt<bool>
+    ClDropTypeTests("lowertypetests-drop-type-tests",
+                    cl::desc("Simply drop type test assume sequences"),
+                    cl::Hidden, cl::init(false));
+
 bool BitSetInfo::containsGlobalOffset(uint64_t Offset) const {
   if (Offset < ByteOffset)
     return false;
@@ -528,7 +533,8 @@
   LowerTypeTests(ModuleSummaryIndex *ExportSummary,
                  const ModuleSummaryIndex *ImportSummary, bool DropTypeTests)
       : ModulePass(ID), ExportSummary(ExportSummary),
-        ImportSummary(ImportSummary), DropTypeTests(DropTypeTests) {
+        ImportSummary(ImportSummary),
+        DropTypeTests(DropTypeTests || ClDropTypeTests) {
     initializeLowerTypeTestsPass(*PassRegistry::getPassRegistry());
   }
 
@@ -1687,7 +1693,7 @@
     Module &M, ModuleSummaryIndex *ExportSummary,
     const ModuleSummaryIndex *ImportSummary, bool DropTypeTests)
     : M(M), ExportSummary(ExportSummary), ImportSummary(ImportSummary),
-      DropTypeTests(DropTypeTests) {
+      DropTypeTests(DropTypeTests || ClDropTypeTests) {
   assert(!(ExportSummary && ImportSummary));
   Triple TargetTriple(M.getTargetTriple());
   Arch = TargetTriple.getArch();
@@ -1793,6 +1799,14 @@
       for (auto CIU = CI->use_begin(), CIUE = CI->use_end(); CIU != CIUE;)
         if (auto *Assume = dyn_cast<AssumeInst>((*CIU++).getUser()))
           Assume->eraseFromParent();
+      // If the assume was merged with another assume, we might have a use on a
+      // phi (which will feed the assume). Simply replace the use on the phi
+      // with "true" and leave the merged assume.
+      if (!CI->use_empty()) {
+        assert(all_of(CI->users(),
+                      [](User *U) -> bool { return isa<PHINode>(U); }));
+        CI->replaceAllUsesWith(ConstantInt::getTrue(M.getContext()));
+      }
       CI->eraseFromParent();
     }
 
diff --git a/llvm/test/Transforms/LowerTypeTests/drop_type_test_phi.ll b/llvm/test/Transforms/LowerTypeTests/drop_type_test_phi.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/Transforms/LowerTypeTests/drop_type_test_phi.ll
@@ -0,0 +1,67 @@
+; Test to ensure dropping of type tests can handle a phi feeding the assume.
+; RUN: opt -S -lowertypetests -lowertypetests-drop-type-tests -mtriple=x86_64-unknown-linux-gnu < %s | FileCheck %s
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-grtev4-linux-gnu"
+
+%struct.A = type { i32 (...)** }
+%struct.B = type { %struct.A }
+%struct.C = type { %struct.A }
+
+@_ZTV1B = constant { [4 x i8*] } { [4 x i8*] [i8* null, i8* undef, i8* bitcast (i32 (%struct.B*, i32)* @_ZN1B1fEi to i8*), i8* bitcast (i32 (%struct.A*, i32)* @_ZN1A1nEi to i8*)] }, !type !0, !type !1
+@_ZTV1C = constant { [4 x i8*] } { [4 x i8*] [i8* null, i8* undef, i8* bitcast (i32 (%struct.C*, i32)* @_ZN1C1fEi to i8*), i8* bitcast (i32 (%struct.A*, i32)* @_ZN1A1nEi to i8*)] }, !type !0, !type !2
+
+; CHECK-LABEL: define i32 @test
+define i32 @test(%struct.A* %obj, i32 %a, i32 %b) {
+entry:
+  %tobool.not = icmp eq i32 %a, 0
+  br i1 %tobool.not, label %if.else, label %if.then
+
+if.then:
+  %0 = bitcast %struct.A* %obj to i8***
+  %vtable = load i8**, i8*** %0
+  %1 = bitcast i8** %vtable to i8*
+  %p = call i1 @llvm.type.test(i8* %1, metadata !"_ZTS1A")
+; CHECK-NOT: @llvm.type.test
+  %fptrptr = getelementptr i8*, i8** %vtable, i32 1
+  %2 = bitcast i8** %fptrptr to i32 (%struct.A*, i32)**
+  %fptr1 = load i32 (%struct.A*, i32)*, i32 (%struct.A*, i32)** %2, align 8
+  %call = tail call i32 %fptr1(%struct.A* nonnull %obj, i32 %a)
+  br label %if.end
+
+if.else:
+  %3 = icmp ne i32 %b, 0
+  br label %if.end
+
+if.end:
+  %4 = phi i1 [ %3, %if.else ], [ %p, %if.then ]
+  call void @llvm.assume(i1 %4)
+; Still have the assume, but the type test target replaced with true.
+; CHECK: %4 = phi i1 [ %3, %if.else ], [ true, %if.then ]
+; CHECK: call void @llvm.assume(i1 %4)
+
+  ret i32 0
+}
+; CHECK-LABEL: ret i32
+; CHECK-LABEL: }
+
+declare i1 @llvm.type.test(i8*, metadata)
+declare void @llvm.assume(i1)
+
+define i32 @_ZN1B1fEi(%struct.B* %this, i32 %a) #0 {
+   ret i32 0;
+}
+
+define i32 @_ZN1A1nEi(%struct.A* %this, i32 %a) #0 {
+   ret i32 0;
+}
+
+define i32 @_ZN1C1fEi(%struct.C* %this, i32 %a) #0 {
+   ret i32 0;
+}
+
+attributes #0 = { noinline optnone }
+
+!0 = !{i64 16, !"_ZTS1A"}
+!1 = !{i64 16, !"_ZTS1B"}
+!2 = !{i64 16, !"_ZTS1C"}