diff --git a/llvm/docs/LangRef.rst b/llvm/docs/LangRef.rst
--- a/llvm/docs/LangRef.rst
+++ b/llvm/docs/LangRef.rst
@@ -12473,11 +12473,10 @@
 Semantics:
 """"""""""
 
-The '``llvm.memcpy.*``' intrinsics copy a block of memory from the
-source location to the destination location, which are not allowed to
-overlap. It copies "len" bytes of memory over. If the argument is known
-to be aligned to some boundary, this can be specified as an attribute on
-the argument.
+The '``llvm.memcpy.*``' intrinsics copy a block of memory from the source
+location to the destination location. It copies "len" bytes of memory over. If
+the argument is known to be aligned to some boundary, this can be specified as
+an attribute on the argument.
 
 If "len" is 0, the pointers may be NULL, dangling, ``undef``, or ``poison``
 pointers. However, they must still be appropriately aligned.
diff --git a/llvm/lib/Analysis/BasicAliasAnalysis.cpp b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
--- a/llvm/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
@@ -981,13 +981,15 @@
   // no-aliases the other.
   if (auto *Inst = dyn_cast<AnyMemCpyInst>(Call)) {
     AliasResult SrcAA, DestAA;
+    SrcAA =
+        getBestAAResults().alias(MemoryLocation::getForSource(Inst), Loc, AAQI);
 
-    if ((SrcAA = getBestAAResults().alias(MemoryLocation::getForSource(Inst),
-                                          Loc, AAQI)) == MustAlias)
+    DestAA =
+        getBestAAResults().alias(MemoryLocation::getForDest(Inst), Loc, AAQI);
+    if (SrcAA == MustAlias && DestAA == NoAlias)
       // Loc is exactly the memcpy source thus disjoint from memcpy dest.
       return ModRefInfo::Ref;
-    if ((DestAA = getBestAAResults().alias(MemoryLocation::getForDest(Inst),
-                                           Loc, AAQI)) == MustAlias)
+    if (DestAA == MustAlias && SrcAA == NoAlias)
       // The converse case.
       return ModRefInfo::Mod;
 
diff --git a/llvm/test/Analysis/BasicAA/assume.ll b/llvm/test/Analysis/BasicAA/assume.ll
--- a/llvm/test/Analysis/BasicAA/assume.ll
+++ b/llvm/test/Analysis/BasicAA/assume.ll
@@ -14,8 +14,8 @@
 ; CHECK: MayAlias:	i8* %P, i8* %Q
 ; CHECK: NoModRef:  Ptr: i8* %P	<->  tail call void @llvm.assume(i1 true)
 ; CHECK: NoModRef:  Ptr: i8* %Q	<->  tail call void @llvm.assume(i1 true)
-; CHECK: Just Mod:  Ptr: i8* %P	<->  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
-; CHECK: Just Ref:  Ptr: i8* %Q	<->  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
+; CHECK: Both ModRef:  Ptr: i8* %P	<->  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
+; CHECK: Both ModRef:  Ptr: i8* %Q	<->  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
 ; CHECK: NoModRef:   tail call void @llvm.assume(i1 true) <->   tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
 ; CHECK: NoModRef:   tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false) <->   tail call void @llvm.assume(i1 true)
 }
diff --git a/llvm/test/Analysis/BasicAA/cs-cs.ll b/llvm/test/Analysis/BasicAA/cs-cs.ll
--- a/llvm/test/Analysis/BasicAA/cs-cs.ll
+++ b/llvm/test/Analysis/BasicAA/cs-cs.ll
@@ -17,12 +17,12 @@
 ; CHECK-LABEL: Function: test2:
 
 ; CHECK:   MayAlias:     i8* %P, i8* %Q
-; CHECK:   Just Mod:  Ptr: i8* %P     <->  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
-; CHECK:   Just Ref:  Ptr: i8* %Q     <->  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
-; CHECK:   Just Mod:  Ptr: i8* %P     <->  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
-; CHECK:   Just Ref:  Ptr: i8* %Q     <->  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
-; CHECK:   Just Mod:   tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false) <->   tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
-; CHECK:   Just Mod:   tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false) <->   tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
+; CHECK:   Both ModRef:  Ptr: i8* %P     <->  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
+; CHECK:   Both ModRef:  Ptr: i8* %Q     <->  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
+; CHECK:   Both ModRef:  Ptr: i8* %P     <->  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
+; CHECK:   Both ModRef:  Ptr: i8* %Q     <->  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
+; CHECK:   Both ModRef:   tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false) <->   tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
+; CHECK:   Both ModRef:   tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false) <->   tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
 }
 
 define void @test2_atomic(i8* %P, i8* %Q) #3 {
@@ -33,12 +33,12 @@
 ; CHECK-LABEL: Function: test2_atomic:
 
 ; CHECK:   MayAlias:     i8* %P, i8* %Q
-; CHECK:   Just Mod:  Ptr: i8* %P     <->  tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 %P, i8* align 1 %Q, i64 12, i32 1)
-; CHECK:   Just Ref:  Ptr: i8* %Q     <->  tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 %P, i8* align 1 %Q, i64 12, i32 1)
-; CHECK:   Just Mod:  Ptr: i8* %P     <->  tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 %P, i8* align 1 %Q, i64 12, i32 1)
-; CHECK:   Just Ref:  Ptr: i8* %Q     <->  tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 %P, i8* align 1 %Q, i64 12, i32 1)
-; CHECK:   Just Mod:   tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 %P, i8* align 1 %Q, i64 12, i32 1) <->   tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 %P, i8* align 1 %Q, i64 12, i32 1)
-; CHECK:   Just Mod:   tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 %P, i8* align 1 %Q, i64 12, i32 1) <->   tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 %P, i8* align 1 %Q, i64 12, i32 1)
+; CHECK:   Both ModRef:  Ptr: i8* %P     <->  tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 %P, i8* align 1 %Q, i64 12, i32 1)
+; CHECK:   Both ModRef:  Ptr: i8* %Q     <->  tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 %P, i8* align 1 %Q, i64 12, i32 1)
+; CHECK:   Both ModRef:  Ptr: i8* %P     <->  tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 %P, i8* align 1 %Q, i64 12, i32 1)
+; CHECK:   Both ModRef:  Ptr: i8* %Q     <->  tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 %P, i8* align 1 %Q, i64 12, i32 1)
+; CHECK:   Both ModRef:   tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 %P, i8* align 1 %Q, i64 12, i32 1) <->   tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 %P, i8* align 1 %Q, i64 12, i32 1)
+; CHECK:   Both ModRef:   tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 %P, i8* align 1 %Q, i64 12, i32 1) <->   tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 %P, i8* align 1 %Q, i64 12, i32 1)
 }
 
 define void @test2a(i8* noalias %P, i8* noalias %Q) #3 {
@@ -149,12 +149,12 @@
 ; CHECK-LABEL: Function: test3:
 
 ; CHECK: MayAlias:     i8* %P, i8* %Q
-; CHECK: Just Mod:  Ptr: i8* %P     <->  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 8, i1 false)
-; CHECK: Just Ref:  Ptr: i8* %Q     <->  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 8, i1 false)
-; CHECK: Just Mod:  Ptr: i8* %P     <->  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
-; CHECK: Just Ref:  Ptr: i8* %Q     <->  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
-; CHECK: Just Mod:   tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 8, i1 false) <->   tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
-; CHECK: Just Mod:   tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false) <->   tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 8, i1 false)
+; CHECK: Both ModRef:  Ptr: i8* %P     <->  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 8, i1 false)
+; CHECK: Both ModRef:  Ptr: i8* %Q     <->  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 8, i1 false)
+; CHECK: Both ModRef:  Ptr: i8* %P     <->  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
+; CHECK: Both ModRef:  Ptr: i8* %Q     <->  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
+; CHECK: Both ModRef:   tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 8, i1 false) <->   tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
+; CHECK: Both ModRef:   tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false) <->   tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 8, i1 false)
 }
 
 define void @test3a(i8* noalias %P, i8* noalias %Q) #3 {
@@ -199,14 +199,14 @@
 ; CHECK: MayAlias:     i8* %P, i8* %Q
 ; CHECK: MayAlias:     i8* %P, i8* %R
 ; CHECK: MayAlias:     i8* %Q, i8* %R
-; CHECK: Just Mod:  Ptr: i8* %P     <->  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
-; CHECK: Just Ref:  Ptr: i8* %Q     <->  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
+; CHECK: Both ModRef:  Ptr: i8* %P     <->  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
+; CHECK: Both ModRef:  Ptr: i8* %Q     <->  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
 ; CHECK: Both ModRef:  Ptr: i8* %R     <->  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
-; CHECK: Just Mod:  Ptr: i8* %P     <->  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %R, i64 12, i1 false)
+; CHECK: Both ModRef:  Ptr: i8* %P     <->  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %R, i64 12, i1 false)
 ; CHECK: Both ModRef:  Ptr: i8* %Q     <->  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %R, i64 12, i1 false)
-; CHECK: Just Ref:  Ptr: i8* %R     <->  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %R, i64 12, i1 false)
-; CHECK: Just Mod:   tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false) <->   tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %R, i64 12, i1 false)
-; CHECK: Just Mod:   tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %R, i64 12, i1 false) <->   tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
+; CHECK: Both ModRef:  Ptr: i8* %R     <->  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %R, i64 12, i1 false)
+; CHECK: Both ModRef:   tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false) <->   tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %R, i64 12, i1 false)
+; CHECK: Both ModRef:   tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %R, i64 12, i1 false) <->   tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
 }
 
 define void @test5a(i8* noalias %P, i8* noalias %Q, i8* noalias %R) nounwind ssp {
diff --git a/llvm/test/Analysis/BasicAA/guards.ll b/llvm/test/Analysis/BasicAA/guards.ll
--- a/llvm/test/Analysis/BasicAA/guards.ll
+++ b/llvm/test/Analysis/BasicAA/guards.ll
@@ -14,8 +14,8 @@
 
 ; CHECK:  Just Ref:  Ptr: i8* %P	<->  tail call void (i1, ...) @llvm.experimental.guard(i1 true) [ "deopt"() ]
 ; CHECK:  Just Ref:  Ptr: i8* %Q	<->  tail call void (i1, ...) @llvm.experimental.guard(i1 true) [ "deopt"() ]
-; CHECK:  Just Mod:  Ptr: i8* %P	<->  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
-; CHECK:  Just Ref:  Ptr: i8* %Q	<->  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
+; CHECK:  Both ModRef:  Ptr: i8* %P	<->  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
+; CHECK:  Both ModRef:  Ptr: i8* %Q	<->  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
 ; CHECK:  Just Ref:   tail call void (i1, ...) @llvm.experimental.guard(i1 true) [ "deopt"() ] <->   tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
 ; CHECK:  Just Mod:   tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false) <->   tail call void (i1, ...) @llvm.experimental.guard(i1 true) [ "deopt"() ]
 }
diff --git a/llvm/test/Analysis/MemorySSA/basicaa-memcpy.ll b/llvm/test/Analysis/MemorySSA/basicaa-memcpy.ll
--- a/llvm/test/Analysis/MemorySSA/basicaa-memcpy.ll
+++ b/llvm/test/Analysis/MemorySSA/basicaa-memcpy.ll
@@ -6,7 +6,7 @@
 ; CHECK-LABEL: @source_clobber(
 ; CHECK-NEXT:  ; 1 = MemoryDef(liveOnEntry)
 ; CHECK-NEXT:    call void @llvm.memcpy.p0i8.p0i8.i64(i8* %a, i8* %b, i64 128, i1 false)
-; CHECK-NEXT:  ; MemoryUse(liveOnEntry)
+; CHECK-NEXT:  ; MemoryUse(1) MayAlias
 ; CHECK-NEXT:    [[X:%.*]] = load i8, i8* %b
 ; CHECK-NEXT:    ret void
 ;
diff --git a/llvm/test/Transforms/DeadStoreElimination/MSSA/memset-and-memcpy.ll b/llvm/test/Transforms/DeadStoreElimination/MSSA/memset-and-memcpy.ll
--- a/llvm/test/Transforms/DeadStoreElimination/MSSA/memset-and-memcpy.ll
+++ b/llvm/test/Transforms/DeadStoreElimination/MSSA/memset-and-memcpy.ll
@@ -74,7 +74,8 @@
 ; Previously this was not allowed (PR8728), also discussed in PR11763.
 define void @test18(i8* %P, i8* %Q, i8* %R) nounwind ssp {
 ; CHECK-LABEL: @test18(
-; CHECK-NEXT:    tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* [[P:%.*]], i8* [[R:%.*]], i64 12, i1 false)
+; CHECK-NEXT:    tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* [[P:%.*]], i8* [[Q:%.*]], i64 12, i1 false)
+; CHECK-NEXT:    tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* [[P]], i8* [[R:%.*]], i64 12, i1 false)
 ; CHECK-NEXT:    ret void
 ;
   tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
@@ -84,7 +85,8 @@
 
 define void @test18_atomic(i8* %P, i8* %Q, i8* %R) nounwind ssp {
 ; CHECK-LABEL: @test18_atomic(
-; CHECK-NEXT:    tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 [[P:%.*]], i8* align 1 [[R:%.*]], i64 12, i32 1)
+; CHECK-NEXT:    tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 [[P:%.*]], i8* align 1 [[Q:%.*]], i64 12, i32 1)
+; CHECK-NEXT:    tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 [[P]], i8* align 1 [[R:%.*]], i64 12, i32 1)
 ; CHECK-NEXT:    ret void
 ;
   tail call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i64(i8* align 1 %P, i8* align 1 %Q, i64 12, i32 1)