[OpenCL] Add as_size/ptrdiff/intptr/uintptr_t operators

[svenvh]

Summary

size_t and friends are built-in scalar data types and s6.4.4.2 of the
OpenCL C Specification says the as_type() operator must be available
for these data types.

[Anastasia]

LGTH! Thanks!

clang/lib/Headers/opencl-c-base.h

 #define as_half(x) __builtin_astype((x), half)
 #define as_half2(x) __builtin_astype((x), half2)
 #define as_half3(x) __builtin_astype((x), half3)
 #define as_half4(x) __builtin_astype((x), half4)
 #define as_half8(x) __builtin_astype((x), half8)
 #define as_half16(x) __builtin_astype((x), half16)
 #endif // cl_khr_fp16
 
+#define as_size_t(x) __builtin_astype((x), size_t)
+#define as_ptrdiff_t(x) __builtin_astype((x), ptrdiff_t)
+#define as_intptr_t(x) __builtin_astype((x), intptr_t)
+#define as_uintptr_t(x) __builtin_astype((x), uintptr_t)
+
 // OpenCL v1.1 s6.9, v1.2/2.0 s6.10 - Function qualifiers
 
 #define __kernel_exec(X, typen) __kernel \
   __attribute__((work_group_size_hint(X, 1, 1))) \
   __attribute__((vec_type_hint(typen)))
 
 #define kernel_exec(X, typen) __kernel \
   __attribute__((work_group_size_hint(X, 1, 1))) \

clang/test/SemaOpenCL/as_type.cl

-// RUN: %clang_cc1 %s -emit-llvm -triple spir-unknown-unknown -finclude-default-header -o - -verify -fsyntax-only
+// RUN: %clang_cc1 %s -emit-llvm -DBITS=32 -triple spir-unknown-unknown -finclude-default-header -fdeclare-opencl-builtins -o - -verify -fsyntax-only
+// RUN: %clang_cc1 %s -emit-llvm -DBITS=64 -triple spir64-unknown-unknown -finclude-default-header -fdeclare-opencl-builtins -o - -verify -fsyntax-only
 
 char3 f1(char16 x) {
   return  __builtin_astype(x, char3); // expected-error{{invalid reinterpretation: sizes of 'char3' (vector of 3 'char' values) and '__private char16' (vector of 16 'char' values) must match}}
 }
 
 char16 f3(int x) {
   return __builtin_astype(x, char16); // expected-error{{invalid reinterpretation: sizes of 'char16' (vector of 16 'char' values) and '__private int' must match}}
 }
 
 void foo() {
     char src = 1;
     int dst = as_int(src); // expected-error{{invalid reinterpretation: sizes of 'int' and '__private char' must match}}
 }
+
+void target_dependent(int i, long l) {
+  size_t size1 = as_size_t(i);
+#if BITS == 64
+  // expected-error@-2{{sizes of 'size_t' (aka 'unsigned long') and '__private int' must match}}
+#endif
+
+  size_t size2 = as_size_t(l);
+#if BITS == 32
+  // expected-error@-2{{sizes of 'size_t' (aka 'unsigned int') and '__private long' must match}}
+#endif
+}