diff --git a/clang/include/clang/Basic/CodeGenOptions.def b/clang/include/clang/Basic/CodeGenOptions.def
--- a/clang/include/clang/Basic/CodeGenOptions.def
+++ b/clang/include/clang/Basic/CodeGenOptions.def
@@ -395,6 +395,10 @@
 /// Whether to not follow the AAPCS that enforce at least one read before storing to a volatile bitfield
 CODEGENOPT(ForceAAPCSBitfieldLoad, 1, 0)
 
+/// Assume that by-value parameters do not alias any other values.
+CODEGENOPT(PassByValueIsNoAlias, 1, 0)
+
+
 #undef CODEGENOPT
 #undef ENUM_CODEGENOPT
 #undef VALUE_CODEGENOPT
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -4314,6 +4314,9 @@
 def fcompatibility_qualified_id_block_param_type_checking : Flag<["-"], "fcompatibility-qualified-id-block-type-checking">,
   HelpText<"Allow using blocks with parameters of more specific type than "
            "the type system guarantees when a parameter is qualified id">;
+def fpass_by_value_is_noalias: Flag<["-"], "fpass-by-value-is-noalias">,
+  HelpText<"Allows assuming by-value parameters do not alias any other value."
+           "Has no effect on non-trivially-copyable classes in C++.">, Group<f_Group>;
 
 // FIXME: Remove these entirely once functionality/tests have been excised.
 def fobjc_gc_only : Flag<["-"], "fobjc-gc-only">, Group<f_Group>,
diff --git a/clang/lib/CodeGen/CGCall.cpp b/clang/lib/CodeGen/CGCall.cpp
--- a/clang/lib/CodeGen/CGCall.cpp
+++ b/clang/lib/CodeGen/CGCall.cpp
@@ -2201,6 +2201,13 @@
       if (AI.getIndirectByVal())
         Attrs.addByValAttr(getTypes().ConvertTypeForMem(ParamType));
 
+      if (CodeGenOpts.PassByValueIsNoAlias &&
+          ParamType.isTriviallyCopyableType(getContext()) &&
+          !ParamType.isObjCGCWeak())
+        // When calling the function, the pointer passed in will be the only
+        // reference to the underlying object. Mark it accordingly.
+        Attrs.addAttribute(llvm::Attribute::NoAlias);
+
       // TODO: We could add the byref attribute if not byval, but it would
       // require updating many testcases.
 
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -1453,6 +1453,8 @@
       std::string(Args.getLastArgValue(OPT_fsymbol_partition_EQ));
 
   Opts.ForceAAPCSBitfieldLoad = Args.hasArg(OPT_ForceAAPCSBitfieldLoad);
+
+  Opts.PassByValueIsNoAlias = Args.hasArg(OPT_fpass_by_value_is_noalias);
   return Success;
 }
 
diff --git a/clang/test/CodeGen/pass-by-value-noalias.c b/clang/test/CodeGen/pass-by-value-noalias.c
new file mode 100644
--- /dev/null
+++ b/clang/test/CodeGen/pass-by-value-noalias.c
@@ -0,0 +1,16 @@
+// RUN: %clang_cc1 -fpass-by-value-is-noalias -triple arm64-apple-iphoneos -emit-llvm -disable-llvm-optzns %s -o - 2>&1 | FileCheck --check-prefix=WITH_NOALIAS %s
+// RUN: %clang_cc1 -triple arm64-apple-iphoneos -emit-llvm -disable-llvm-optzns %s -o - 2>&1 | FileCheck --check-prefix=NO_NOALIAS %s
+
+// A struct large enough so it is not passed in registers on ARM64.
+struct Foo {
+  int a;
+  int b;
+  int c;
+  int d;
+  int e;
+  int f;
+};
+
+// WITH_NOALIAS: define void @take(%struct.Foo* noalias %arg)
+// NO_NOALIAS: define void @take(%struct.Foo* %arg)
+void take(struct Foo arg) {}
diff --git a/clang/test/CodeGenCXX/pass-by-value-noalias.cpp b/clang/test/CodeGenCXX/pass-by-value-noalias.cpp
new file mode 100644
--- /dev/null
+++ b/clang/test/CodeGenCXX/pass-by-value-noalias.cpp
@@ -0,0 +1,43 @@
+// RUN: %clang_cc1 -fpass-by-value-is-noalias -triple arm64-apple-iphoneos -emit-llvm -disable-llvm-optzns %s -o - 2>&1 | FileCheck --check-prefix=WITH_NOALIAS %s
+// RUN: %clang_cc1 -triple arm64-apple-iphoneos -emit-llvm -disable-llvm-optzns %s -o - 2>&1 | FileCheck --check-prefix=NO_NOALIAS %s
+
+// A trivial struct large enough so it is not passed in registers on ARM64.
+struct Foo {
+  int a;
+  int b;
+  int c;
+  int d;
+  int e;
+  int f;
+};
+
+// Make sure noalias is added to indirect arguments with trivially copyable types
+// if -fpass-by-value-is-noalias is provided.
+
+// WITH_NOALIAS: define void @_Z4take3Foo(%struct.Foo* noalias %arg)
+// NO_NOALIAS: define void @_Z4take3Foo(%struct.Foo* %arg)
+void take(Foo arg) {}
+
+int G;
+
+// NonTrivial is not trivially-copyable, because it has a non-trivial copy
+// constructor.
+struct NonTrivial {
+  int a;
+  int b;
+  int c;
+  int d;
+  int e;
+  int f;
+
+  NonTrivial(const NonTrivial &Other) {
+    a = G + 10 + Other.a;
+  }
+};
+
+// Make sure noalias is not added to indirect arguments that are not trivially
+// copyable even if -fpass-by-value-is-noalias is provided.
+
+// WITH_NOALIAS: define void @_Z4take10NonTrivial(%struct.NonTrivial* %arg)
+// NO_NOALIAS:   define void @_Z4take10NonTrivial(%struct.NonTrivial* %arg)
+void take(NonTrivial arg) {}
diff --git a/clang/test/CodeGenObjC/pass-by-value-noalias.m b/clang/test/CodeGenObjC/pass-by-value-noalias.m
new file mode 100644
--- /dev/null
+++ b/clang/test/CodeGenObjC/pass-by-value-noalias.m
@@ -0,0 +1,21 @@
+// RUN: %clang_cc1 -fpass-by-value-is-noalias -triple arm64-apple-iphoneos -emit-llvm -disable-llvm-optzns -fobjc-runtime-has-weak -fobjc-arc -fobjc-dispatch-method=mixed %s -o - 2>&1 | FileCheck --check-prefix=WITH_NOALIAS %s
+// RUN: %clang_cc1 -triple arm64-apple-iphoneos -emit-llvm -disable-llvm-optzns -fobjc-runtime-has-weak -fobjc-arc -fobjc-dispatch-method=mixed %s -o - 2>&1 | FileCheck --check-prefix=NO_NOALIAS %s
+
+// A struct large enough so it is not passed in registers on ARM64.
+
+@interface Bar
+@property char value;
+@end
+
+struct Foo {
+  int a;
+  int b;
+  int c;
+  int d;
+  int e;
+  Bar *__weak f;
+};
+
+// WITH_NOALIAS: define void @take(%struct.Foo* noalias %arg)
+// NO_NOALIAS: define void @take(%struct.Foo* %arg)
+void take(struct Foo arg) {}