diff --git a/clang/include/clang/Basic/Builtins.def b/clang/include/clang/Basic/Builtins.def
--- a/clang/include/clang/Basic/Builtins.def
+++ b/clang/include/clang/Basic/Builtins.def
@@ -1569,6 +1569,9 @@
 
 // Invariants
 BUILTIN(__builtin_assume, "vb", "nE")
+// facebook begin T130678741
+BUILTIN(__builtin_experimental_separate_storage, "vvCD*vCD*", "nE")
+// facebook end T130678741
 
 // Multiprecision Arithmetic Builtins.
 BUILTIN(__builtin_addcb, "UcUcCUcCUcCUc*", "n")
diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -13318,6 +13318,9 @@
   bool SemaBuiltinAllocaWithAlign(CallExpr *TheCall);
   bool SemaBuiltinArithmeticFence(CallExpr *TheCall);
   bool SemaBuiltinAssume(CallExpr *TheCall);
+  // facebook begin T130678741
+  bool SemaBuiltinExperimentalSeparateStorage(CallExpr *TheCall);
+  // facebook end T130678741
   bool SemaBuiltinAssumeAligned(CallExpr *TheCall);
   bool SemaBuiltinLongjmp(CallExpr *TheCall);
   bool SemaBuiltinSetjmp(CallExpr *TheCall);
diff --git a/clang/lib/CodeGen/CGBuiltin.cpp b/clang/lib/CodeGen/CGBuiltin.cpp
--- a/clang/lib/CodeGen/CGBuiltin.cpp
+++ b/clang/lib/CodeGen/CGBuiltin.cpp
@@ -2806,6 +2806,22 @@
     Function *FnAssume = CGM.getIntrinsic(Intrinsic::assume);
     return RValue::get(Builder.CreateCall(FnAssume, ArgValue));
   }
+  // facebook begin T130678741
+  case Builtin::BI__builtin_experimental_separate_storage: {
+    // We copy __builtin_assume's semantics and don't let side-effecting
+    // expressions do anything. Maybe this is the wrong thing?
+    const Expr *Arg0 = E->getArg(0);
+    const Expr *Arg1 = E->getArg(1);
+    if (Arg0->HasSideEffects(getContext()) ||
+        Arg1->HasSideEffects(getContext()))
+      return RValue::get(nullptr);
+
+    Value *Arg0Value = EmitScalarExpr(Arg0);
+    Value *Arg1Value = EmitScalarExpr(Arg1);
+    Function *Fn = CGM.getIntrinsic(Intrinsic::experimental_separate_storage);
+    return RValue::get(Builder.CreateCall(Fn, {Arg0Value, Arg1Value}));
+  }
+  // facebook end T130678741
   case Builtin::BI__arithmetic_fence: {
     // Create the builtin call if FastMath is selected, and the target
     // supports the builtin, otherwise just return the argument.
diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -2162,6 +2162,12 @@
     if (SemaBuiltinAssume(TheCall))
       return ExprError();
     break;
+  // facebook begin T130678741
+  case Builtin::BI__builtin_experimental_separate_storage:
+    if (SemaBuiltinExperimentalSeparateStorage(TheCall))
+      return ExprError();
+    break;
+  // facebook end T130678741
   case Builtin::BI__builtin_assume_aligned:
     if (SemaBuiltinAssumeAligned(TheCall))
       return ExprError();
@@ -7623,6 +7629,28 @@
   return false;
 }
 
+// facebook begin T130678741
+bool Sema::SemaBuiltinExperimentalSeparateStorage(CallExpr *TheCall) {
+  Expr *Arg0 = TheCall->getArg(0);
+  Expr *Arg1 = TheCall->getArg(1);
+
+  // We don't actually have semantics for what happens when there are
+  // side-effecting operations inside the separate storage hint.
+
+  if (!Arg0->isInstantiationDependent() && Arg0->HasSideEffects(Context))
+    Diag(Arg0->getBeginLoc(), diag::warn_assume_side_effects)
+        << Arg0->getSourceRange()
+        << cast<FunctionDecl>(TheCall->getCalleeDecl())->getIdentifier();
+
+  if (!Arg1->isInstantiationDependent() && Arg1->HasSideEffects(Context))
+    Diag(Arg1->getBeginLoc(), diag::warn_assume_side_effects)
+        << Arg1->getSourceRange()
+        << cast<FunctionDecl>(TheCall->getCalleeDecl())->getIdentifier();
+
+  return false;
+}
+// facebook end T130678741
+
 /// Handle __builtin_alloca_with_align. This is declared
 /// as (size_t, size_t) where the second size_t must be a power of 2 greater
 /// than 8.
diff --git a/clang/test/CodeGen/builtin-experimental-separate-storage.c b/clang/test/CodeGen/builtin-experimental-separate-storage.c
new file mode 100644
--- /dev/null
+++ b/clang/test/CodeGen/builtin-experimental-separate-storage.c
@@ -0,0 +1,39 @@
+// facebook begin T130678741
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown -emit-llvm -o - %s | FileCheck %s
+void *nonconst(void);
+void *isconst(void) __attribute__((const));
+void *ispure(void) __attribute__((pure));
+
+// CHECK-LABEL: @test1
+void test1(int *a, int *b) {
+  // CHECK: store ptr %a, ptr [[A_ADDR:%.+]], align
+  // CHECK: store ptr %b, ptr [[B_ADDR:%.+]], align
+  // CHECK: [[A:%.+]] = load ptr, ptr [[A_ADDR]]
+  // CHECK: [[B:%.+]] = load ptr, ptr [[B_ADDR]]
+
+  // CHECK: call void @llvm.experimental.separate.storage(ptr [[A]], ptr [[B]])
+  __builtin_experimental_separate_storage(a, b);
+}
+
+// CHECK-LABEL: @test2
+void test2(int *a, int *b) {
+  // CHECK-NOT: call void @llvm.experimental.separate.storage
+  // CHECK-NOT: call i32 @nonconst()
+  __builtin_experimental_separate_storage(a, nonconst());
+  __builtin_experimental_separate_storage(a++, b++);
+}
+
+// CHECK_LABEL @test3
+void test3(int *a) {
+  // CHECK: call ptr @isconst()
+  // CHECK: call void @llvm.experimental.separate.storage
+  __builtin_experimental_separate_storage(a, isconst());
+}
+
+// CHECK_LABEL @test4
+void test4(int *a) {
+  // CHECK: call ptr @ispure()
+  // CHECK: call void @llvm.experimental.separate.storage
+  __builtin_experimental_separate_storage(a, ispure());
+}
+// facebook end T130678741
diff --git a/clang/test/Sema/builtin-experimental-separate-storage.c b/clang/test/Sema/builtin-experimental-separate-storage.c
new file mode 100644
--- /dev/null
+++ b/clang/test/Sema/builtin-experimental-separate-storage.c
@@ -0,0 +1,14 @@
+// facebook begin T130678741
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown -fsyntax-only -verify %s
+
+void *nonconst(void);
+
+void test1(int *a, int *b) {
+  __builtin_experimental_separate_storage(a, b);
+  __builtin_experimental_separate_storage(a++, b); // expected-warning {{the argument to '__builtin_experimental_separate_storage' has side effects that will be discarded}}
+  __builtin_experimental_separate_storage(nonconst(), a); // expected-warning {{the argument to '__builtin_experimental_separate_storage' has side effects that will be discarded}}
+  __builtin_experimental_separate_storage(a, nonconst()); // expected-warning {{the argument to '__builtin_experimental_separate_storage' has side effects that will be discarded}}
+  __builtin_experimental_separate_storage(a, 3); // expected-error {{incompatible integer to pointer conversion}}
+  __builtin_experimental_separate_storage(3, a); // expected-error {{incompatible integer to pointer conversion}}
+}
+// facebook end T130678741