[v2] RISC-V: Add riscv_vector_cc function attribute

From: xuli <xuli1@eswincomputing.com>

Standard vector calling convention variant will only enabled when function
has vector argument or returning value by default, however user may also
want to invoke function without that during a vectorized loop at some situation,
but it will cause a huge performance penalty due to vector register store/restore.

So user can declare function with this riscv_vector_cc attribute like below, that could enforce
function will use standard vector calling convention variant.

void foo() __attribute__((riscv_vector_cc));
[[riscv::vector_cc]] void foo(); // For C++11 and C23

For more details please reference the below link.
https://github.com/riscv-non-isa/riscv-c-api-doc/pull/67

gcc/ChangeLog:

	* config/riscv/riscv.cc (TARGET_GNU_ATTRIBUTES): Add riscv_vector_cc
	attribute to riscv_attribute_table.
	(riscv_vector_cc_function_p): Return true if FUNC is a riscv_vector_cc function.
	(riscv_fntype_abi): Add riscv_vector_cc attribute check.
	* doc/extend.texi: Add riscv_vector_cc attribute description.

gcc/testsuite/ChangeLog:

	* g++.target/riscv/rvv/base/attribute-riscv_vector_cc-error.C: New test.
	* gcc.target/riscv/rvv/base/attribute-riscv_vector_cc-callee-saved.c: New test.
	* gcc.target/riscv/rvv/base/attribute-riscv_vector_cc-error.c: New test.
---
 gcc/config/riscv/riscv.cc                     | 55 ++++++++++++++++---
 gcc/doc/extend.texi                           | 10 ++++
 .../base/attribute-riscv_vector_cc-error.C    | 21 +++++++
 .../attribute-riscv_vector_cc-callee-saved.c  | 30 ++++++++++
 .../base/attribute-riscv_vector_cc-error.c    | 11 ++++
 5 files changed, 119 insertions(+), 8 deletions(-)
 create mode 100644 gcc/testsuite/g++.target/riscv/rvv/base/attribute-riscv_vector_cc-error.C
 create mode 100644 gcc/testsuite/gcc.target/riscv/rvv/base/attribute-riscv_vector_cc-callee-saved.c
 create mode 100644 gcc/testsuite/gcc.target/riscv/rvv/base/attribute-riscv_vector_cc-error.c

LGTM, thanks :)

On Fri, Mar 1, 2024 at 5:10 PM Li Xu <xuli1@eswincomputing.com> wrote:
>
> From: xuli <xuli1@eswincomputing.com>
>
> Standard vector calling convention variant will only enabled when function
> has vector argument or returning value by default, however user may also
> want to invoke function without that during a vectorized loop at some situation,
> but it will cause a huge performance penalty due to vector register store/restore.
>
> So user can declare function with this riscv_vector_cc attribute like below, that could enforce
> function will use standard vector calling convention variant.
>
> void foo() __attribute__((riscv_vector_cc));
> [[riscv::vector_cc]] void foo(); // For C++11 and C23
>
> For more details please reference the below link.
> https://github.com/riscv-non-isa/riscv-c-api-doc/pull/67
>
> gcc/ChangeLog:
>
>         * config/riscv/riscv.cc (TARGET_GNU_ATTRIBUTES): Add riscv_vector_cc
>         attribute to riscv_attribute_table.
>         (riscv_vector_cc_function_p): Return true if FUNC is a riscv_vector_cc function.
>         (riscv_fntype_abi): Add riscv_vector_cc attribute check.
>         * doc/extend.texi: Add riscv_vector_cc attribute description.
>
> gcc/testsuite/ChangeLog:
>
>         * g++.target/riscv/rvv/base/attribute-riscv_vector_cc-error.C: New test.
>         * gcc.target/riscv/rvv/base/attribute-riscv_vector_cc-callee-saved.c: New test.
>         * gcc.target/riscv/rvv/base/attribute-riscv_vector_cc-error.c: New test.
> ---
>  gcc/config/riscv/riscv.cc                     | 55 ++++++++++++++++---
>  gcc/doc/extend.texi                           | 10 ++++
>  .../base/attribute-riscv_vector_cc-error.C    | 21 +++++++
>  .../attribute-riscv_vector_cc-callee-saved.c  | 30 ++++++++++
>  .../base/attribute-riscv_vector_cc-error.c    | 11 ++++
>  5 files changed, 119 insertions(+), 8 deletions(-)
>  create mode 100644 gcc/testsuite/g++.target/riscv/rvv/base/attribute-riscv_vector_cc-error.C
>  create mode 100644 gcc/testsuite/gcc.target/riscv/rvv/base/attribute-riscv_vector_cc-callee-saved.c
>  create mode 100644 gcc/testsuite/gcc.target/riscv/rvv/base/attribute-riscv_vector_cc-error.c
>
> diff --git a/gcc/config/riscv/riscv.cc b/gcc/config/riscv/riscv.cc
> index 4100abc9dd1..7f37f231796 100644
> --- a/gcc/config/riscv/riscv.cc
> +++ b/gcc/config/riscv/riscv.cc
> @@ -537,24 +537,52 @@ static tree riscv_handle_fndecl_attribute (tree *, tree, tree, int, bool *);
>  static tree riscv_handle_type_attribute (tree *, tree, tree, int, bool *);
>
>  /* Defining target-specific uses of __attribute__.  */
> -TARGET_GNU_ATTRIBUTES (riscv_attribute_table,
> +static const attribute_spec riscv_gnu_attributes[] =
>  {
>    /* Syntax: { name, min_len, max_len, decl_required, type_required,
>                function_type_required, affects_type_identity, handler,
>                exclude } */
>
>    /* The attribute telling no prologue/epilogue.  */
> -  { "naked",   0,  0, true, false, false, false,
> -    riscv_handle_fndecl_attribute, NULL },
> +  {"naked", 0, 0, true, false, false, false, riscv_handle_fndecl_attribute,
> +   NULL},
>    /* This attribute generates prologue/epilogue for interrupt handlers.  */
> -  { "interrupt", 0, 1, false, true, true, false,
> -    riscv_handle_type_attribute, NULL },
> +  {"interrupt", 0, 1, false, true, true, false, riscv_handle_type_attribute,
> +   NULL},
>
>    /* The following two are used for the built-in properties of the Vector type
>       and are not used externally */
>    {"RVV sizeless type", 4, 4, false, true, false, true, NULL, NULL},
> -  {"RVV type", 0, 0, false, true, false, true, NULL, NULL}
> -});
> +  {"RVV type", 0, 0, false, true, false, true, NULL, NULL},
> +  /* This attribute is used to declare a function, forcing it to use the
> +    standard vector calling convention variant. Syntax:
> +    __attribute__((riscv_vector_cc)). */
> +  {"riscv_vector_cc", 0, 0, false, true, true, true, NULL, NULL}
> +};
> +
> +static const scoped_attribute_specs riscv_gnu_attribute_table  =
> +{
> +  "gnu", {riscv_gnu_attributes}
> +};
> +
> +static const attribute_spec riscv_attributes[] =
> +{
> +  /* This attribute is used to declare a function, forcing it to use the
> +     standard vector calling convention variant. Syntax:
> +     [[riscv::vector_cc]]. */
> +  {"vector_cc", 0, 0, false, true, true, true, NULL, NULL}
> +};
> +
> +static const scoped_attribute_specs riscv_nongnu_attribute_table =
> +{
> +  "riscv", {riscv_attributes}
> +};
> +
> +static const scoped_attribute_specs *const riscv_attribute_table[] =
> +{
> +  &riscv_gnu_attribute_table,
> +  &riscv_nongnu_attribute_table
> +};
>
>  /* Order for the CLOBBERs/USEs of gpr_save.  */
>  static const unsigned gpr_save_reg_order[] = {
> @@ -5425,6 +5453,16 @@ riscv_arguments_is_vector_type_p (const_tree fntype)
>    return false;
>  }
>
> +/* Return true if FUNC is a riscv_vector_cc function.
> +   For more details please reference the below link.
> +   https://github.com/riscv-non-isa/riscv-c-api-doc/pull/67 */
> +static bool
> +riscv_vector_cc_function_p (const_tree fntype)
> +{
> +  return lookup_attribute ("vector_cc", TYPE_ATTRIBUTES (fntype)) != NULL_TREE
> +        || lookup_attribute ("riscv_vector_cc", TYPE_ATTRIBUTES (fntype)) != NULL_TREE;
> +}
> +
>  /* Implement TARGET_FNTYPE_ABI.  */
>
>  static const predefined_function_abi &
> @@ -5434,7 +5472,8 @@ riscv_fntype_abi (const_tree fntype)
>       reference the below link.
>       https://github.com/riscv-non-isa/riscv-elf-psabi-doc/pull/389  */
>    if (riscv_return_value_is_vector_type_p (fntype)
> -         || riscv_arguments_is_vector_type_p (fntype))
> +         || riscv_arguments_is_vector_type_p (fntype)
> +         || riscv_vector_cc_function_p (fntype))
>      return riscv_v_abi ();
>
>    return default_function_abi;
> diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
> index 2135dfde9c8..bc8126d2840 100644
> --- a/gcc/doc/extend.texi
> +++ b/gcc/doc/extend.texi
> @@ -6314,6 +6314,16 @@ Permissible values for this parameter are @code{user}, @code{supervisor},
>  and @code{machine}.  If there is no parameter, then it defaults to
>  @code{machine}.
>
> +@cindex @code{riscv_vector_cc} function attribute, RISC-V
> +@item riscv_vector_cc
> +Use this attribute to force the function to use the vector calling
> +convention variant.
> +
> +@smallexample
> +void foo() __attribute__((riscv_vector_cc));
> +[[riscv::vector_cc]] void foo(); // For C++11 and C23
> +@end smallexample
> +
>  @end table
>
>  The following target-specific function attributes are available for the
> diff --git a/gcc/testsuite/g++.target/riscv/rvv/base/attribute-riscv_vector_cc-error.C b/gcc/testsuite/g++.target/riscv/rvv/base/attribute-riscv_vector_cc-error.C
> new file mode 100644
> index 00000000000..63a353bebd0
> --- /dev/null
> +++ b/gcc/testsuite/g++.target/riscv/rvv/base/attribute-riscv_vector_cc-error.C
> @@ -0,0 +1,21 @@
> +/* { dg-do compile } */
> +/* { dg-options "-march=rv64gcv -mabi=lp64d -O1" } */
> +
> +[[riscv::vector_cc]] void foo();// For C++11 and C23
> +
> +[[riscv::vector_cc]] int var; /* { dg-warning "'vector_cc' attribute only applies to function types" } */
> +
> +void __attribute__((riscv_vector_cc)) func();
> +void __attribute__((riscv_vector_cc(1))) func_invalid(); /* { dg-error "wrong number of arguments specified for 'riscv_vector_cc' attribute" } */
> +
> +void test_no_attribute(int);
> +void  __attribute__((riscv_vector_cc)) test_no_attribute(int x) { }
> +
> +class test_cc {
> +   __attribute__((riscv_vector_cc)) void member_func();
> +};
> +
> +void test_lambda() {
> +   __attribute__((riscv_vector_cc)) auto lambda = []() { /* { dg-warning "'riscv_vector_cc' attribute only applies to function types" } */
> +  };
> +}
> diff --git a/gcc/testsuite/gcc.target/riscv/rvv/base/attribute-riscv_vector_cc-callee-saved.c b/gcc/testsuite/gcc.target/riscv/rvv/base/attribute-riscv_vector_cc-callee-saved.c
> new file mode 100644
> index 00000000000..b47ecb3b828
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/riscv/rvv/base/attribute-riscv_vector_cc-callee-saved.c
> @@ -0,0 +1,30 @@
> +/* { dg-do compile } */
> +/* { dg-options "-march=rv64gcv -mabi=lp64d" } */
> +
> +void __attribute__((riscv_vector_cc)) bar1 (int a);
> +void bar2 ();
> +
> +void __attribute__((riscv_vector_cc))
> +foo1 (int a)
> +{
> +  bar1 (a);
> +}
> +
> +void __attribute__((riscv_vector_cc))
> +foo2 (int a)
> +{
> +  char data[1024];
> +  bar2 ();
> +}
> +
> +void
> +foo3 (int *a)
> +{
> +  bar1 (*a);
> +}
> +
> +/* { dg-final { scan-assembler-not {\.variant_cc\tbar2} } } */
> +/* { dg-final { scan-assembler-not {\.variant_cc\tfoo3} } } */
> +/* { dg-final { scan-assembler-times {\.variant_cc\tbar1} 1 } } */
> +/* { dg-final { scan-assembler-times {\.variant_cc\tfoo1} 1 } } */
> +/* { dg-final { scan-assembler-times {\.variant_cc\tfoo2} 1 } } */
> diff --git a/gcc/testsuite/gcc.target/riscv/rvv/base/attribute-riscv_vector_cc-error.c b/gcc/testsuite/gcc.target/riscv/rvv/base/attribute-riscv_vector_cc-error.c
> new file mode 100644
> index 00000000000..ceb5e5bf6dd
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/riscv/rvv/base/attribute-riscv_vector_cc-error.c
> @@ -0,0 +1,11 @@
> +/* { dg-do compile } */
> +/* { dg-options "-march=rv64gcv -mabi=lp64d -O1" } */
> +
> +__attribute__((riscv_vector_cc)) int var; /* { dg-warning "'riscv_vector_cc' attribute only applies to function types" } */
> +[[riscv::vector_cc]] int var1; /* { dg-warning "'vector_cc' attribute only applies to function types" } */
> +
> +void __attribute__((riscv_vector_cc)) func();
> +void __attribute__((riscv_vector_cc(1))) func_invalid(); /* { dg-error "wrong number of arguments specified for 'riscv_vector_cc' attribute" } */
> +
> +void test_no_attribute(int);
> +void __attribute__((riscv_vector_cc)) test_no_attribute(int x) { }
> --
> 2.17.1
>