Index: lib/AST/ExprConstant.cpp
===================================================================
--- lib/AST/ExprConstant.cpp
+++ lib/AST/ExprConstant.cpp
@@ -8155,6 +8155,121 @@
   case Builtin::BIomp_is_initial_device:
     // We can decide statically which value the runtime would return if called.
     return Success(Info.getLangOpts().OpenMPIsDevice ? 0 : 1, E);
+  case Builtin::BI__builtin_add_overflow:
+  case Builtin::BI__builtin_sub_overflow:
+  case Builtin::BI__builtin_mul_overflow:
+  case Builtin::BI__builtin_sadd_overflow:
+  case Builtin::BI__builtin_uadd_overflow:
+  case Builtin::BI__builtin_uaddl_overflow:
+  case Builtin::BI__builtin_uaddll_overflow:
+  case Builtin::BI__builtin_usub_overflow:
+  case Builtin::BI__builtin_usubl_overflow:
+  case Builtin::BI__builtin_usubll_overflow:
+  case Builtin::BI__builtin_umul_overflow:
+  case Builtin::BI__builtin_umull_overflow:
+  case Builtin::BI__builtin_umulll_overflow:
+  case Builtin::BI__builtin_saddl_overflow:
+  case Builtin::BI__builtin_saddll_overflow:
+  case Builtin::BI__builtin_ssub_overflow:
+  case Builtin::BI__builtin_ssubl_overflow:
+  case Builtin::BI__builtin_ssubll_overflow:
+  case Builtin::BI__builtin_smul_overflow:
+  case Builtin::BI__builtin_smull_overflow:
+  case Builtin::BI__builtin_smulll_overflow: {
+    LValue ResultLValue;
+    APSInt LHS, RHS;
+
+    QualType ResultType = E->getArg(2)->getType()->getPointeeType();
+    if (!EvaluateInteger(E->getArg(0), LHS, Info) ||
+        !EvaluateInteger(E->getArg(1), RHS, Info) ||
+        !EvaluatePointer(E->getArg(2), ResultLValue, Info))
+      return false;
+
+    APSInt Result;
+    bool DidOverflow = false;
+
+    // If the types don't have to match, enlarge all 3 to the largest of them.
+    if (BuiltinOp == Builtin::BI__builtin_add_overflow ||
+        BuiltinOp == Builtin::BI__builtin_sub_overflow ||
+        BuiltinOp == Builtin::BI__builtin_mul_overflow) {
+      bool IsSigned = LHS.isSigned() || RHS.isSigned() ||
+                      ResultType->isSignedIntegerOrEnumerationType();
+      bool AllSigned = LHS.isSigned() && RHS.isSigned() &&
+                      ResultType->isSignedIntegerOrEnumerationType();
+      uint64_t LHSSize = LHS.getBitWidth();
+      uint64_t RHSSize = RHS.getBitWidth();
+      uint64_t ResultSize = Info.Ctx.getTypeSize(ResultType);
+      uint64_t MaxBits = std::max(std::max(LHSSize, RHSSize), ResultSize);
+
+      // Add an additional bit if the signedness isn't uniformly agreed to. We
+      // could do this ONLY if there is a signed and an unsigned that both have
+      // MaxBits, but the code to check that is pretty nasty.  The issue will be
+      // caught in the shrink-to-result later anyway.
+      if (IsSigned && !AllSigned)
+        ++MaxBits;
+
+      LHS = APSInt(IsSigned ? LHS.sextOrSelf(MaxBits) : LHS.zextOrSelf(MaxBits),
+                   !IsSigned);
+      RHS = APSInt(IsSigned ? RHS.sextOrSelf(MaxBits) : RHS.zextOrSelf(MaxBits),
+                   !IsSigned);
+      Result = APSInt(MaxBits, !IsSigned);
+    }
+
+    // Find largest int.
+    switch (BuiltinOp) {
+    default:
+      llvm_unreachable("Invalid value for BuiltinOp");
+    case Builtin::BI__builtin_add_overflow:
+    case Builtin::BI__builtin_sadd_overflow:
+    case Builtin::BI__builtin_saddl_overflow:
+    case Builtin::BI__builtin_saddll_overflow:
+    case Builtin::BI__builtin_uadd_overflow:
+    case Builtin::BI__builtin_uaddl_overflow:
+    case Builtin::BI__builtin_uaddll_overflow:
+      Result = LHS.isSigned() ? LHS.sadd_ov(RHS, DidOverflow)
+                              : LHS.uadd_ov(RHS, DidOverflow);
+      break;
+    case Builtin::BI__builtin_sub_overflow:
+    case Builtin::BI__builtin_ssub_overflow:
+    case Builtin::BI__builtin_ssubl_overflow:
+    case Builtin::BI__builtin_ssubll_overflow:
+    case Builtin::BI__builtin_usub_overflow:
+    case Builtin::BI__builtin_usubl_overflow:
+    case Builtin::BI__builtin_usubll_overflow:
+      Result = LHS.isSigned() ? LHS.ssub_ov(RHS, DidOverflow)
+                              : LHS.usub_ov(RHS, DidOverflow);
+      break;
+    case Builtin::BI__builtin_mul_overflow:
+    case Builtin::BI__builtin_smul_overflow:
+    case Builtin::BI__builtin_smull_overflow:
+    case Builtin::BI__builtin_smulll_overflow:
+    case Builtin::BI__builtin_umul_overflow:
+    case Builtin::BI__builtin_umull_overflow:
+    case Builtin::BI__builtin_umulll_overflow:
+      Result = LHS.isSigned() ? LHS.smul_ov(RHS, DidOverflow)
+                              : LHS.umul_ov(RHS, DidOverflow);
+      break;
+    }
+
+    // In the case where multiple sizes are allowed, truncate and see if
+    // the values are the same.
+    if (BuiltinOp == Builtin::BI__builtin_add_overflow ||
+        BuiltinOp == Builtin::BI__builtin_sub_overflow ||
+        BuiltinOp == Builtin::BI__builtin_mul_overflow) {
+      // It won't GROW, since that isn't possible, so use this to allow
+      // TruncOrSelf.
+      APSInt Temp = Result.extOrTrunc(Info.Ctx.getTypeSize(ResultType));
+      Temp.setIsSigned(ResultType->isSignedIntegerOrEnumerationType());
+
+      if (!APSInt::isSameValue(Temp, Result))
+        DidOverflow = true;
+      Result = Temp;
+    }
+
+    APValue APV{Result};
+    handleAssignment(Info, E, ResultLValue, ResultType, APV);
+    return Success(DidOverflow, E);
+  }
   }
 }
 
Index: lib/Sema/SemaChecking.cpp
===================================================================
--- lib/Sema/SemaChecking.cpp
+++ lib/Sema/SemaChecking.cpp
@@ -197,13 +197,17 @@
 
   // First two arguments should be integers.
   for (unsigned I = 0; I < 2; ++I) {
-    Expr *Arg = TheCall->getArg(I);
-    QualType Ty = Arg->getType();
+    ExprResult Arg = TheCall->getArg(I);
+    QualType Ty = Arg.get()->getType();
     if (!Ty->isIntegerType()) {
-      S.Diag(Arg->getLocStart(), diag::err_overflow_builtin_must_be_int)
-          << Ty << Arg->getSourceRange();
+      S.Diag(Arg.get()->getLocStart(), diag::err_overflow_builtin_must_be_int)
+          << Ty << Arg.get()->getSourceRange();
       return true;
     }
+    InitializedEntity Entity = InitializedEntity::InitializeParameter(
+        S.getASTContext(), Ty, /*consume*/ false);
+    Arg = S.PerformCopyInitialization(Entity, SourceLocation(), Arg);
+    TheCall->setArg(I, Arg.get());
   }
 
   // Third argument should be a pointer to a non-const integer.
Index: test/SemaCXX/builtins-overflow.cpp
===================================================================
--- test/SemaCXX/builtins-overflow.cpp
+++ test/SemaCXX/builtins-overflow.cpp
@@ -0,0 +1,74 @@
+// RUN: %clang_cc1 -fsyntax-only -std=c++17 -verify %s
+// expected-no-diagnostics
+
+#include <limits.h>
+#define OVERFLOWS 103
+
+
+template <typename RET, typename LHS, typename RHS>
+constexpr RET add(LHS &&lhs, RHS &&rhs) {
+  RET sum{};
+  return __builtin_add_overflow(lhs, rhs, &sum) ? OVERFLOWS : sum;
+}
+
+static_assert(add<short>(static_cast<char>(120), static_cast<char>(10)) == 130);
+static_assert(add<short>(static_cast<char>(120), static_cast<short>(10)) == 130);
+static_assert(add<char>(static_cast<short>(120), static_cast<short>(10)) == OVERFLOWS);
+static_assert(add<unsigned int>(INT_MAX, INT_MAX) == static_cast<unsigned int>(INT_MAX) * 2u);
+static_assert(add<int>(static_cast<unsigned int>(INT_MAX), 1u) == OVERFLOWS);
+
+static_assert(add<int>(17, 22) == 39);
+static_assert(add<int>(INT_MAX - 22, 23) == OVERFLOWS);
+static_assert(add<int>(INT_MIN + 22, -23) == OVERFLOWS);
+
+template <typename RET, typename LHS, typename RHS>
+constexpr RET sub(LHS &&lhs, RHS &&rhs) {
+  RET sum{};
+  return __builtin_sub_overflow(lhs, rhs, &sum) ? OVERFLOWS : sum;
+}
+
+static_assert(sub<unsigned char>(static_cast<char>(0),static_cast<char>(1)) == OVERFLOWS);
+static_assert(sub<char>(static_cast<unsigned char>(0),static_cast<unsigned char>(1)) == -1);
+static_assert(sub<unsigned short>(static_cast<short>(0),static_cast<short>(1)) == OVERFLOWS);
+
+static_assert(sub<int>(17,22) == -5);
+static_assert(sub<int>(INT_MAX - 22, -23) == OVERFLOWS);
+static_assert(sub<int>(INT_MIN + 22, 23) == OVERFLOWS);
+
+template <typename RET, typename LHS, typename RHS>
+constexpr RET mul(LHS &&lhs, RHS &&rhs) {
+  RET sum{};
+  return __builtin_mul_overflow(lhs, rhs, &sum) ? OVERFLOWS : sum;
+}
+
+static_assert(mul<int>(17,22) == 374);
+static_assert(mul<int>(INT_MAX / 22, 23) == OVERFLOWS);
+static_assert(mul<int>(INT_MIN / 22, -23) == OVERFLOWS);
+
+constexpr auto sadd(int lhs, int rhs) {
+  int sum{};
+  return __builtin_sadd_overflow(lhs, rhs, &sum) ? OVERFLOWS : sum;
+}
+
+static_assert(sadd(17,22) == 39);
+static_assert(sadd(INT_MAX - 22, 23) == OVERFLOWS);
+static_assert(sadd(INT_MIN + 22, -23) == OVERFLOWS);
+
+constexpr auto ssub(int lhs, int rhs) {
+  int sum{};
+  return __builtin_ssub_overflow(lhs, rhs, &sum) ? OVERFLOWS : sum;
+}
+
+static_assert(ssub(17,22) == -5);
+static_assert(ssub(INT_MAX - 22, -23) == OVERFLOWS);
+static_assert(ssub(INT_MIN + 22, 23) == OVERFLOWS);
+
+constexpr auto smul(int lhs, int rhs) {
+  int sum{};
+  return __builtin_smul_overflow(lhs, rhs, &sum) ? OVERFLOWS : sum;
+}
+
+static_assert(smul(17,22) == 374);
+static_assert(smul(INT_MAX / 22, 23) == OVERFLOWS);
+static_assert(smul(INT_MIN / 22, -23) == OVERFLOWS);
+