[OpenCL] Allow undefining cl_khr_integer_dot_product features macros

Add header-side undef hooks for:
  __opencl_c_integer_dot_product_input_4x8bit
  __opencl_c_integer_dot_product_input_4x8bit_packed

Motivation: our downstream legacy targets lack cl_khr_integer_dot_product
builtins (similar to a60b8f4). Providing __undef__* macros lets
users suppress the feature macros without patching headers.

Fix intel/compute-runtime#817

Author: wenju-he

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

@@ -53,6 +53,13 @@
 #define __opencl_c_kernel_clock_scope_work_group 1
 #define __opencl_c_kernel_clock_scope_sub_group 1
 
+#ifdef __undef___opencl_c_integer_dot_product_input_4x8bit
+#undef __opencl_c_integer_dot_product_input_4x8bit
+#endif
+#ifdef __undef___opencl_c_integer_dot_product_input_4x8bit_packed
+#undef __opencl_c_integer_dot_product_input_4x8bit_packed
+#endif
+
 #endif // defined(__SPIR__) || defined(__SPIRV__)
 #endif // (defined(__OPENCL_CPP_VERSION__) || __OPENCL_C_VERSION__ >= 200)
 

clang/test/SemaOpenCL/features.cl

@@ -26,6 +26,12 @@
 // RUN: %clang_cc1 -triple spir-unknown-unknown %s -E -dM -o - -x cl -cl-std=clc++1.0 \
 // RUN:   | FileCheck -match-full-lines %s  --check-prefix=NO-FEATURES
 
+// For OpenCL C 2.0, header-only features can be disabled using macros.
+// RUN: %clang_cc1 -triple spir-unknown-unknown %s -E -dM -o - -x cl -cl-std=CL2.0 -fdeclare-opencl-builtins -finclude-default-header \
+// RUN:    -D__undef___opencl_c_integer_dot_product_input_4x8bit \
+// RUN:    -D__undef___opencl_c_integer_dot_product_input_4x8bit_packed \
+// RUN:   | FileCheck %s --check-prefix=NO-HEADERONLY-FEATURES-CL20
+
 // For OpenCL C 3.0, header-only features can be disabled using macros.
 // RUN: %clang_cc1 -triple spir-unknown-unknown %s -E -dM -o - -x cl -cl-std=CL3.0 -fdeclare-opencl-builtins -finclude-default-header \
 // RUN:    -D__undef___opencl_c_work_group_collective_functions=1 \
@@ -64,6 +70,9 @@
 // NO-FEATURES-NOT: #define __opencl_c_read_write_images
 // NO-FEATURES-NOT: #define __opencl_c_subgroups
 
+// NO-HEADERONLY-FEATURES-CL20-NOT: #define __opencl_c_integer_dot_product_input_4x8bit
+// NO-HEADERONLY-FEATURES-CL20-NOT: #define __opencl_c_integer_dot_product_input_4x8bit_packed
+
 // NO-HEADERONLY-FEATURES-NOT: #define __opencl_c_work_group_collective_functions
 // NO-HEADERONLY-FEATURES-NOT: #define __opencl_c_atomic_order_seq_cst
 // NO-HEADERONLY-FEATURES-NOT: #define __opencl_c_atomic_scope_device