Add additional testcases for nsw markings on ++ and --.

clang has generated correct IR for char/short decrement since r126816,
but we didn't have any test coverage for decrement.

Patch by Andrew Rogers.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@291805 91177308-0d34-0410-b5e6-96231b3b80d8

test/CodeGen/integer-overflow.c

@@ -65,13 +65,37 @@ void test1() {
   // TRAPV: getelementptr inbounds i32, i32*
   // CATCH_UB: getelementptr inbounds i32, i32*
 
-  // PR9350: char increment never overflows.
-  extern volatile signed char PR9350;
+  // PR9350: char pre-increment never overflows.
+  extern volatile signed char PR9350_char_inc;
   // DEFAULT: add i8 {{.*}}, 1
   // WRAPV: add i8 {{.*}}, 1
   // TRAPV: add i8 {{.*}}, 1
   // CATCH_UB: add i8 {{.*}}, 1
-  ++PR9350;
+  ++PR9350_char_inc;
+
+  // PR9350: char pre-decrement never overflows.
+  extern volatile signed char PR9350_char_dec;
+  // DEFAULT: add i8 {{.*}}, -1
+  // WRAPV: add i8 {{.*}}, -1
+  // TRAPV: add i8 {{.*}}, -1
+  // CATCH_UB: add i8 {{.*}}, -1
+  --PR9350_char_dec;
+
+  // PR9350: short pre-increment never overflows.
+  extern volatile signed short PR9350_short_inc;
+  // DEFAULT: add i16 {{.*}}, 1
+  // WRAPV: add i16 {{.*}}, 1
+  // TRAPV: add i16 {{.*}}, 1
+  // CATCH_UB: add i16 {{.*}}, 1
+  ++PR9350_short_inc;
+
+  // PR9350: short pre-decrement never overflows.
+  extern volatile signed short PR9350_short_dec;
+  // DEFAULT: add i16 {{.*}}, -1
+  // WRAPV: add i16 {{.*}}, -1
+  // TRAPV: add i16 {{.*}}, -1
+  // CATCH_UB: add i16 {{.*}}, -1
+  --PR9350_short_dec;
 
   // PR24256: don't instrument __builtin_frame_address.
   __builtin_frame_address(0 + 0);