RISC-V: Add norelax function attribute

This patch adds norelax function attribute that be discussed in riscv-c-api-doc PR#94.
URL:riscv-non-isa/riscv-c-api-doc#94

gcc/ChangeLog:

	* config/riscv/riscv.cc (riscv_declare_function_name): Add new
	attribute.

gcc/config/riscv/riscv.cc

@@ -654,6 +654,10 @@ static const attribute_spec riscv_gnu_attributes[] =
      types.  */
   {"riscv_rvv_vector_bits", 1, 1, false, true, false, true,
    riscv_handle_rvv_vector_bits_attribute, NULL},
+  /* This attribute is used to declare a function, forcing it to use the
+    standard vector calling convention variant. Syntax:
+    __attribute__((norelax)). */
+  {"norelax", 0, 0, true, false, false, false, NULL, NULL},
 };
 
 static const scoped_attribute_specs riscv_gnu_attribute_table  =
@@ -10051,24 +10055,31 @@ riscv_declare_function_name (FILE *stream, const char *name, tree fndecl)
   riscv_asm_output_variant_cc (stream, fndecl, name);
   ASM_OUTPUT_TYPE_DIRECTIVE (stream, name, "function");
   ASM_OUTPUT_FUNCTION_LABEL (stream, name, fndecl);
-  if (DECL_FUNCTION_SPECIFIC_TARGET (fndecl))
+  if (DECL_FUNCTION_SPECIFIC_TARGET (fndecl)
+      || lookup_attribute ("norelax", DECL_ATTRIBUTES (fndecl)))
     {
       fprintf (stream, "\t.option push\n");
+      if (lookup_attribute ("norelax", DECL_ATTRIBUTES (fndecl)))
+	{
+	  fprintf (stream, "\t.option norelax\n");
+	}
+      if (DECL_FUNCTION_SPECIFIC_TARGET (fndecl))
+	{
+	  struct cl_target_option *local_cl_target
+	    = TREE_TARGET_OPTION (DECL_FUNCTION_SPECIFIC_TARGET (fndecl));
+	  struct cl_target_option *global_cl_target
+	    = TREE_TARGET_OPTION (target_option_default_node);
 
-      struct cl_target_option *local_cl_target =
-	TREE_TARGET_OPTION (DECL_FUNCTION_SPECIFIC_TARGET (fndecl));
-      struct cl_target_option *global_cl_target =
-	TREE_TARGET_OPTION (target_option_default_node);
-
-      const char *local_arch_str = get_arch_str (local_cl_target);
-      const char *arch_str = local_arch_str != NULL
-	? local_arch_str
-	: riscv_arch_str (true).c_str ();
-      fprintf (stream, "\t.option arch, %s\n", arch_str);
-      const char *local_tune_str = get_tune_str (local_cl_target);
-      const char *global_tune_str = get_tune_str (global_cl_target);
-      if (strcmp (local_tune_str, global_tune_str) != 0)
-	fprintf (stream, "\t# tune = %s\n", local_tune_str);
+	  const char *local_arch_str = get_arch_str (local_cl_target);
+	  const char *arch_str = local_arch_str != NULL
+				   ? local_arch_str
+				   : riscv_arch_str (true).c_str ();
+	  fprintf (stream, "\t.option arch, %s\n", arch_str);
+	  const char *local_tune_str = get_tune_str (local_cl_target);
+	  const char *global_tune_str = get_tune_str (global_cl_target);
+	  if (strcmp (local_tune_str, global_tune_str) != 0)
+	    fprintf (stream, "\t# tune = %s\n", local_tune_str);
+	}
     }
 }
 
@@ -10078,7 +10089,8 @@ riscv_declare_function_size (FILE *stream, const char *name, tree fndecl)
   if (!flag_inhibit_size_directive)
     ASM_OUTPUT_MEASURED_SIZE (stream, name);
 
-  if (DECL_FUNCTION_SPECIFIC_TARGET (fndecl))
+  if (DECL_FUNCTION_SPECIFIC_TARGET (fndecl)
+      || lookup_attribute ("norelax", DECL_ATTRIBUTES (fndecl)))
     {
       fprintf (stream, "\t.option pop\n");
     }

gcc/testsuite/gcc.target/riscv/target-attr-norelax.c

@@ -0,0 +1,21 @@
+/* { dg-do compile } */
+/* { dg-options "-march=rv32gc" { target { rv32 } } } */
+/* { dg-options "-march=rv64gc" { target { rv64 } } } */
+
+__attribute__((norelax))
+void foo1()
+{}
+
+void foo2(void)
+{}
+
+int main()
+{
+  foo1();
+  foo2();
+  return 0;
+}
+
+/* { dg-final { scan-assembler-times ".option push\t" 1 } } */
+/* { dg-final { scan-assembler-times ".option norelax\t" 1 } } */
+/* { dg-final { scan-assembler-times ".option pop\t" 1 } } */