Re: [PATCH] libgccjit: Add support for `restrict` attribute on function parameters

[David Malcolm <dmalcolm@redhat.com>]

On Wed, 2023-08-16 at 22:06 +0200, Guillaume Gomez via Jit wrote:
> My apologies, forgot to run the commit checkers. Here's the commit
> with the errors fixed.
> 
> Le mer. 16 août 2023 à 18:32, Guillaume Gomez
> <guillaume1.gomez@gmail.com> a écrit :
> > 
> > Hi,

Hi Guillaume, thanks for the patch.

> > 
> > This patch adds the possibility to specify the __restrict__
> > attribute
> > for function parameters. It is used by the Rust GCC backend.

What kind of testing has the patch had? (e.g. did you run "make check-
jit" ?  Has this been in use on real Rust code?)

Overall, this patch looks close to being ready, but some nits below...

[...]

> diff --git a/gcc/jit/libgccjit.h b/gcc/jit/libgccjit.h
> index 60eaf39bff6..2e0d08a06d8 100644
> --- a/gcc/jit/libgccjit.h
> +++ b/gcc/jit/libgccjit.h
> @@ -635,6 +635,10 @@ gcc_jit_type_get_const (gcc_jit_type *type);
>  extern gcc_jit_type *
>  gcc_jit_type_get_volatile (gcc_jit_type *type);
>  
> +/* Given type "T", get type "restrict T".  */
> +extern gcc_jit_type *
> +gcc_jit_type_get_restrict (gcc_jit_type *type);
> +
>  #define LIBGCCJIT_HAVE_SIZED_INTEGERS
>  
>  /* Given types LTYPE and RTYPE, return non-zero if they are
compatible.

Please add a feature macro:
#define LIBGCCJIT_HAVE_gcc_jit_type_get_restrict
(see the similar ones in the header).

> diff --git a/gcc/jit/libgccjit.map b/gcc/jit/libgccjit.map
> index e52de0057a5..b7289b13845 100644
> --- a/gcc/jit/libgccjit.map
> +++ b/gcc/jit/libgccjit.map
> @@ -104,6 +104,7 @@ LIBGCCJIT_ABI_0
>      gcc_jit_type_as_object;
>      gcc_jit_type_get_const;
>      gcc_jit_type_get_pointer;
> +    gcc_jit_type_get_restrict;
>      gcc_jit_type_get_volatile;

Please add a new ABI tag (LIBGCCJIT_ABI_25 ?), rather than adding this
to ABI_0.

> diff --git a/gcc/testsuite/jit.dg/test-restrict.c
b/gcc/testsuite/jit.dg/test-restrict.c
> new file mode 100644
> index 00000000000..4c8c4407f91
> --- /dev/null
> +++ b/gcc/testsuite/jit.dg/test-restrict.c
> @@ -0,0 +1,77 @@
> +/* { dg-do compile { target x86_64-*-* } } */
> +
> +#include <stdlib.h>
> +#include <stdio.h>
> +
> +#include "libgccjit.h"
> +
> +/* We don't want set_options() in harness.h to set -O3 to see that
the cold
> +	 attribute affects the optimizations. */

This refers to a "cold attribute"; is this a vestige of a copy-and-
paste from a different test case?

I see that the test scans the generated assembler.  Does the test
actually verify that restrict has an effect, or was that another
vestige from a different test case?

> +#define TEST_ESCHEWS_SET_OPTIONS
> +static void set_options (gcc_jit_context *ctxt, const char *argv0)
> +{
> +	// Set "-O3".
> +	gcc_jit_context_set_int_option(ctxt,
GCC_JIT_INT_OPTION_OPTIMIZATION_LEVEL, 3);
> +}
> +
> +#define TEST_COMPILING_TO_FILE
> +#define OUTPUT_KIND      GCC_JIT_OUTPUT_KIND_ASSEMBLER
> +#define OUTPUT_FILENAME  "output-of-test-restrict.c.s"
> +#include "harness.h"
> +
> +void
> +create_code (gcc_jit_context *ctxt, void *user_data)
> +{
> +	/* Let's try to inject the equivalent of:
> +void t(int *__restrict__ a, int *__restrict__ b, char *__restrict__
c) {
> +	*a += *c;
> +	*b += *c;
> +}
> +	*/
> +	gcc_jit_type *int_type =
> +		gcc_jit_context_get_type (ctxt, GCC_JIT_TYPE_INT);
> +	gcc_jit_type *pint_type = gcc_jit_type_get_pointer(int_type);
> +	gcc_jit_type *pint_restrict_type =
gcc_jit_type_get_restrict(pint_type);
> +
> +	gcc_jit_type *void_type =
> +		gcc_jit_context_get_type (ctxt, GCC_JIT_TYPE_VOID);
> +
> +	gcc_jit_param *a =
> +		gcc_jit_context_new_param (ctxt, NULL,
pint_restrict_type, "a");
> +	gcc_jit_param *b =
> +		gcc_jit_context_new_param (ctxt, NULL,
pint_restrict_type, "b");
> +	gcc_jit_param *c =
> +		gcc_jit_context_new_param (ctxt, NULL,
pint_restrict_type, "c");
> +	gcc_jit_param *params[3] = {a, b, c};
> +
> +	gcc_jit_function *func_t =
> +		gcc_jit_context_new_function (ctxt, NULL,
> +					GCC_JIT_FUNCTION_EXPORTED,
> +					void_type,
> +					"t",
> +					3, params,
> +					0);
> +
> +	gcc_jit_block *block = gcc_jit_function_new_block (func_t,
NULL);
> +
> +	/* *a += *c; */
> +	gcc_jit_block_add_assignment_op (
> +		block, NULL,
> +		gcc_jit_rvalue_dereference (gcc_jit_param_as_rvalue
(a), NULL),
> +		GCC_JIT_BINARY_OP_PLUS,
> +		gcc_jit_lvalue_as_rvalue (
> +			gcc_jit_rvalue_dereference
(gcc_jit_param_as_rvalue (c), NULL)));
> +	/* *b += *c; */
> +	gcc_jit_block_add_assignment_op (
> +		block, NULL,
> +		gcc_jit_rvalue_dereference (gcc_jit_param_as_rvalue
(b), NULL),
> +		GCC_JIT_BINARY_OP_PLUS,
> +		gcc_jit_lvalue_as_rvalue (
> +			gcc_jit_rvalue_dereference
(gcc_jit_param_as_rvalue (c), NULL)));
> +
> +	gcc_jit_block_end_with_void_return (block, NULL);
> +}
> +
> +/* { dg-final { jit-verify-output-file-was-created "" } } */
> +/* { dg-final { jit-verify-assembler-output "addl	%eax, (%rdi)
> +	addl	%eax, (%rsi)" } } */
> -- 
> 2.34.1
> 

If this test is meant to run at -O3 and thus can't be part of test-
combination.c, please add a comment about it to
gcc/testsuite/jit.dg/all-non-failing-tests.h (in the alphabetical
place).

The patch also needs to add documentation for the new entrypoint (in 
topics/types.rst), and for the new ABI tag (in
topics/compatibility.rst).


Thanks again for the patch; hope the above is constructive
Dave