[RISCV][Clang] Add C API header for elw CORE-V intrinsics.

This commit adds the C API header to serve as an interface for
the intrinsic functions provided with the CORE-V xcvelw extension.

The commit includes the addition of the header itself and a clang
CodeGen test that checks the integrity of the call to the wrapper
functions designed in the C API CORE-V elw header.

clang/lib/Headers/CMakeLists.txt

@@ -94,6 +94,7 @@ set(ppc_htm_files
 
 set(riscv_files
   riscv_corev_bitmanip.h
+  riscv_corev_elw.h
   )
 
 set(systemz_files

clang/lib/Headers/riscv_corev_elw.h

@@ -0,0 +1,33 @@
+/*===---- riscv_corev_elw.h - CORE-V event load intrinsics -----------------===
+ *
+ * Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+ * See https://llvm.org/LICENSE.txt for license information.
+ * SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+ *
+ *===-----------------------------------------------------------------------===
+ */
+
+#ifndef __RISCV_COREV_ELW_H
+#define __RISCV_COREV_ELW_H
+
+#include <stdint.h>
+
+#if defined(__cplusplus)
+extern "C" {
+#endif
+
+#if defined(__riscv_xcvelw)
+
+#define __DEFAULT_FN_ATTRS __attribute__((__always_inline__, __nodebug__))
+
+static __inline__ unsigned long __DEFAULT_FN_ATTRS __riscv_cv_elw_elw(void *loc) {
+  return __builtin_riscv_cv_elw_elw(loc);
+}
+
+#endif // defined(__riscv_xcvelw)
+
+#if defined(__cplusplus)
+}
+#endif
+
+#endif // define __RISCV_COREV_ELW_H

clang/test/CodeGen/RISCV/corev-intrinsics/elw-c-api.c

@@ -0,0 +1,11 @@
+// RUN: %clang_cc1 -triple riscv32 -target-feature +xcvelw -emit-llvm %s -o - \
+// RUN:     | FileCheck %s
+
+#include <stdint.h>
+#include <riscv_corev_elw.h>
+
+// CHECK-LABEL: @test_elw
+// CHECK: @llvm.riscv.cv.elw.elw
+uint32_t test_elw(void *a) {
+	return __riscv_cv_elw_elw(a);
+}