Index: lib/Transforms/Utils/SimplifyLibCalls.cpp
===================================================================
--- lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -189,10 +189,16 @@
 static void annotateDereferenceableBytes(CallInst *CI,
                                          ArrayRef<unsigned> ArgNos,
                                          uint64_t DereferenceableBytes) {
+  Function *F = CI->getFunction();
+  if (!F)
+    return;
   for (unsigned ArgNo : ArgNos) {
-    uint64_t DerefBytes = std::max(
-        CI->getDereferenceableOrNullBytes(ArgNo + AttributeList::FirstArgIndex),
-        DereferenceableBytes);
+    uint64_t DerefBytes = DereferenceableBytes;
+    unsigned AS = CI->getArgOperand(ArgNo)->getType()->getPointerAddressSpace();
+    if (AS == 0 && !F->nullPointerIsDefined())
+      DerefBytes = std::max(CI->getDereferenceableOrNullBytes(
+                                ArgNo + AttributeList::FirstArgIndex),
+                            DereferenceableBytes);
 
     if (CI->getDereferenceableBytes(ArgNo + AttributeList::FirstArgIndex) <
         DerefBytes) {
Index: test/Transforms/InstCombine/mem-deref-bytes-addrspaces.ll
===================================================================
--- test/Transforms/InstCombine/mem-deref-bytes-addrspaces.ll
+++ test/Transforms/InstCombine/mem-deref-bytes-addrspaces.ll
@@ -0,0 +1,13 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -instcombine  -S < %s | FileCheck %s
+
+declare i32 @memcmp(i8 addrspace(1)* nocapture, i8* nocapture, i64)
+
+define i32 @memcmp_const_size_update_deref8(i8 addrspace(1)* nocapture readonly %d, i8* nocapture readonly %s) "null-pointer-is-valid"="true" {
+; CHECK-LABEL: @memcmp_const_size_update_deref8(
+; CHECK-NEXT:    [[CALL:%.*]] = tail call i32 @memcmp(i8 addrspace(1)* dereferenceable(16) [[D:%.*]], i8* dereferenceable(16) [[S:%.*]], i64 16)
+; CHECK-NEXT:    ret i32 [[CALL]]
+;
+  %call = tail call i32 @memcmp(i8 addrspace(1)* dereferenceable_or_null(40) %d, i8* %s, i64 16)
+  ret i32 %call
+}
Index: test/Transforms/InstCombine/mem-deref-bytes.ll
===================================================================
--- test/Transforms/InstCombine/mem-deref-bytes.ll
+++ test/Transforms/InstCombine/mem-deref-bytes.ll
@@ -55,7 +55,7 @@
   ret i32 %call
 }
 
-define i32 @memcmp_const_size_update_deref5(i8* nocapture readonly %d, i8* nocapture readonly %s) {
+define i32 @memcmp_const_size_update_deref5(i8* nocapture readonly %d, i8* nocapture readonly %s) "null-pointer-is-valid"="false" {
 ; CHECK-LABEL: @memcmp_const_size_update_deref5(
 ; CHECK-NEXT:    [[CALL:%.*]] = tail call i32 @memcmp(i8* dereferenceable(40) [[D:%.*]], i8* dereferenceable(16) [[S:%.*]], i64 16)
 ; CHECK-NEXT:    ret i32 [[CALL]]
@@ -64,6 +64,15 @@
   ret i32 %call
 }
 
+define i32 @memcmp_const_size_update_deref6(i8* nocapture readonly %d, i8* nocapture readonly %s) "null-pointer-is-valid"="true" {
+; CHECK-LABEL: @memcmp_const_size_update_deref6(
+; CHECK-NEXT:    [[CALL:%.*]] = tail call i32 @memcmp(i8* dereferenceable(16) [[D:%.*]], i8* dereferenceable(16) [[S:%.*]], i64 16)
+; CHECK-NEXT:    ret i32 [[CALL]]
+;
+  %call = tail call i32 @memcmp(i8* dereferenceable_or_null(40) %d, i8* %s, i64 16)
+  ret i32 %call
+}
+
 define i32 @memcmp_const_size_no_update_deref(i8* nocapture readonly %d, i8* nocapture readonly %s) {
 ; CHECK-LABEL: @memcmp_const_size_no_update_deref(
 ; CHECK-NEXT:    [[CALL:%.*]] = tail call i32 @memcmp(i8* dereferenceable(40) [[D:%.*]], i8* dereferenceable(20) [[S:%.*]], i64 16)