[driver] Test that last option wins between -Ofast and -O2.

Part of rdar://13622687

llvm-svn: 180207

clang/test/Driver/Ofast.c

 // RUN: %clang -Ofast -### %s 2>&1 | FileCheck -check-prefix=CHECK-OFAST %s
+// RUN: %clang -O2 -Ofast -### %s 2>&1 | FileCheck -check-prefix=CHECK-OFAST %s
 // RUN: %clang -fno-fast-math -Ofast -### %s 2>&1 | FileCheck -check-prefix=CHECK-OFAST %s
 // RUN: %clang -fno-strict-aliasing -Ofast -### %s 2>&1 | FileCheck -check-prefix=CHECK-OFAST %s
 // RUN: %clang -fno-vectorize -Ofast -### %s 2>&1 | FileCheck -check-prefix=CHECK-OFAST %s
+// RUN: %clang -Ofast -O2 -### %s 2>&1 | FileCheck -check-prefix=CHECK-OFAST-O2 %s
 // RUN: %clang -Ofast -fno-fast-math -### %s 2>&1 | FileCheck -check-prefix=CHECK-OFAST-NO-FAST-MATH %s
 // RUN: %clang -Ofast -fno-strict-aliasing -### %s 2>&1 | FileCheck -check-prefix=CHECK-OFAST-NO-STRICT-ALIASING %s
 // RUN: %clang -Ofast -fno-vectorize -### %s 2>&1 | FileCheck -check-prefix=CHECK-OFAST-NO-VECTORIZE %s
@@ -12,6 +14,12 @@
 // CHECK-OFAST: -Ofast
 // CHECK-OFAST: -vectorize-loops
 
+// CHECK-OFAST-O2: -cc1
+// CHECK-OFAST-O2-NOT: -relaxed-aliasing
+// CHECK-OFAST-O2-NOT: -ffast-math
+// CHECK-OFAST-O2-NOT: -Ofast
+// CHECK-OFAST-O2: -vectorize-loops
+
 // CHECK-OFAST-NO-FAST-MATH: -cc1
 // CHECK-OFAST-NO-FAST-MATH-NOT: -relaxed-aliasing
 // CHECK-OFAST-NO-FAST-MATH-NOT: -ffast-math