OpenCL: Mark printf format string argument

[arsenm]

Summary

Fixes not warning on format string errors.

[arsenm]

ping

[Anastasia]

LGTM! Thanks! Sorry I missed this somehow.

[arsenm]

r343653

[jprice]

This change has caused Clang to start emitting erroneous warnings when using OpenCL's vector specifier, e.g. "%v4f", which doesn't seem to be covered by the format string analysis.

lib/Headers/opencl-c.h

 half16 __ovld __cnfn shuffle2(half4 x, half4 y, ushort16 mask);
 half16 __ovld __cnfn shuffle2(half8 x, half8 y, ushort16 mask);
 half16 __ovld __cnfn shuffle2(half16 x, half16 y, ushort16 mask);
 #endif //cl_khr_fp16
 
 #if __OPENCL_C_VERSION__ >= CL_VERSION_1_2
 // OpenCL v1.2 s6.12.13, v2.0 s6.13.13 - printf
 
-int printf(__constant const char* st, ...);
+int printf(__constant const char* st, ...) __attribute__((format(printf, 1, 2)));
 #endif
 
 // OpenCL v1.1 s6.11.3, v1.2 s6.12.14, v2.0 s6.13.14 - Image Read and Write Functions
 
 // These values need to match the runtime equivalent
 //
 // Addressing Mode.
 //

test/SemaOpenCL/printf-format-string-warnings.cl

+// RUN: %clang_cc1 %s -verify -pedantic -fsyntax-only -cl-std=CL2.0 -finclude-default-header
+
+// Make sure warnings are produced based on printf format strings.
+
+
+kernel void format_string_warnings(__constant char* arg) {
+
+  printf("%d", arg); // expected-warning {{format specifies type 'int' but the argument has type '__constant char *'}}
+
+  printf("not enough arguments %d %d", 4); // expected-warning {{more '%' conversions than data arguments}}
+
+  printf("too many arguments", 4); // expected-warning {{data argument not used by format string}}
+}