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
@@ -392,6 +392,7 @@
 
 // Access to floating point environment
 BUILTIN(__builtin_flt_rounds, "i", "n")
+BUILTIN(__builtin_flt_rounds_set, "vi", "n")
 
 // C99 complex builtins
 BUILTIN(__builtin_cabs, "dXd", "Fne")
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
@@ -3361,6 +3361,14 @@
     return RValue::get(Result);
   }
 
+  case Builtin::BI__builtin_flt_rounds_set: {
+    Function *F = CGM.getIntrinsic(Intrinsic::set_rounding);
+
+    Value *V = EmitScalarExpr(E->getArg(0));
+    Builder.CreateCall(F, V);
+    return RValue::get(nullptr);
+  }
+
   case Builtin::BI__builtin_fpclassify: {
     CodeGenFunction::CGFPOptionsRAII FPOptsRAII(*this, E);
     // FIXME: for strictfp/IEEE-754 we need to not trap on SNaN here.
diff --git a/clang/test/CodeGen/builtins.c b/clang/test/CodeGen/builtins.c
--- a/clang/test/CodeGen/builtins.c
+++ b/clang/test/CodeGen/builtins.c
@@ -278,6 +278,9 @@
 
   res = __builtin_flt_rounds();
   // CHECK: call i32 @llvm.get.rounding(
+
+  __builtin_flt_rounds_set(1);
+  // CHECK: call void @llvm.set.rounding(i32 1)
 }
 
 // CHECK-LABEL: define{{.*}} void @test_float_builtin_ops