.. Copyright (C) 2014-2022 Free Software Foundation, Inc. Originally contributed by David Malcolm This is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see . .. default-domain:: c Compilation contexts ==================== .. type:: gcc_jit_context The top-level of the API is the :c:type:`gcc_jit_context` type. A :c:type:`gcc_jit_context` instance encapsulates the state of a compilation. You can set up options on it, and add types, functions and code. Invoking :c:func:`gcc_jit_context_compile` on it gives you a :c:type:`gcc_jit_result`. Lifetime-management ------------------- Contexts are the unit of lifetime-management within the API: objects have their lifetime bounded by the context they are created within, and cleanup of such objects is done for you when the context is released. .. function:: gcc_jit_context *gcc_jit_context_acquire (void) This function acquires a new :c:type:`gcc_jit_context *` instance, which is independent of any others that may be present within this process. .. function:: void gcc_jit_context_release (gcc_jit_context *ctxt) This function releases all resources associated with the given context. Both the context itself and all of its :c:type:`gcc_jit_object *` instances are cleaned up. It should be called exactly once on a given context. It is invalid to use the context or any of its "contextual" objects after calling this. .. code-block:: c gcc_jit_context_release (ctxt); .. function:: gcc_jit_context * gcc_jit_context_new_child_context (gcc_jit_context *parent_ctxt) Given an existing JIT context, create a child context. The child inherits a copy of all option-settings from the parent. The child can reference objects created within the parent, but not vice-versa. The lifetime of the child context must be bounded by that of the parent: you should release a child context before releasing the parent context. If you use a function from a parent context within a child context, you have to compile the parent context before you can compile the child context, and the gcc_jit_result of the parent context must outlive the gcc_jit_result of the child context. This allows caching of shared initializations. For example, you could create types and declarations of global functions in a parent context once within a process, and then create child contexts whenever a function or loop becomes hot. Each such child context can be used for JIT-compiling just one function or loop, but can reference types and helper functions created within the parent context. Contexts can be arbitrarily nested, provided the above rules are followed, but it's probably not worth going above 2 or 3 levels, and there will likely be a performance hit for such nesting. Thread-safety ------------- Instances of :c:type:`gcc_jit_context *` created via :c:func:`gcc_jit_context_acquire` are independent from each other: only one thread may use a given context at once, but multiple threads could each have their own contexts without needing locks. Contexts created via :c:func:`gcc_jit_context_new_child_context` are related to their parent context. They can be partitioned by their ultimate ancestor into independent "family trees". Only one thread within a process may use a given "family tree" of such contexts at once, and if you're using multiple threads you should provide your own locking around entire such context partitions. .. _error-handling: Error-handling -------------- Various kinds of errors are possible when using the API, such as mismatched types in an assignment. You can only compile and get code from a context if no errors occur. Errors are printed on stderr and can be queried using :c:func:`gcc_jit_context_get_first_error`. They typically contain the name of the API entrypoint where the error occurred, and pertinent information on the problem: .. code-block:: console ./buggy-program: error: gcc_jit_block_add_assignment: mismatching types: assignment to i (type: int) from "hello world" (type: const char *) In general, if an error occurs when using an API entrypoint, the entrypoint returns NULL. You don't have to check everywhere for NULL results, since the API handles a NULL being passed in for any argument by issuing another error. This typically leads to a cascade of followup error messages, but is safe (albeit verbose). The first error message is usually the one to pay attention to, since it is likely to be responsible for all of the rest: .. function:: const char *\ gcc_jit_context_get_first_error (gcc_jit_context *ctxt) Returns the first error message that occurred on the context. The returned string is valid for the rest of the lifetime of the context. If no errors occurred, this will be NULL. If you are wrapping the C API for a higher-level language that supports exception-handling, you may instead be interested in the last error that occurred on the context, so that you can embed this in an exception: .. function:: const char *\ gcc_jit_context_get_last_error (gcc_jit_context *ctxt) Returns the last error message that occurred on the context. If no errors occurred, this will be NULL. If non-NULL, the returned string is only guaranteed to be valid until the next call to libgccjit relating to this context. Debugging --------- .. function:: void\ gcc_jit_context_dump_to_file (gcc_jit_context *ctxt,\ const char *path,\ int update_locations) To help with debugging: dump a C-like representation to the given path, describing what's been set up on the context. If "update_locations" is true, then also set up :type:`gcc_jit_location` information throughout the context, pointing at the dump file as if it were a source file. This may be of use in conjunction with :macro:`GCC_JIT_BOOL_OPTION_DEBUGINFO` to allow stepping through the code in a debugger. .. function:: void\ gcc_jit_context_set_logfile (gcc_jit_context *ctxt,\ FILE *logfile,\ int flags,\ int verbosity) To help with debugging; enable ongoing logging of the context's activity to the given file. For example, the following will enable logging to stderr. .. code-block:: c gcc_jit_context_set_logfile (ctxt, stderr, 0, 0); Examples of information logged include: * API calls * the various steps involved within compilation * activity on any :c:type:`gcc_jit_result` instances created by the context * activity within any child contexts An example of a log can be seen :ref:`here `, though the precise format and kinds of information logged is subject to change. The caller remains responsible for closing `logfile`, and it must not be closed until all users are released. In particular, note that child contexts and :c:type:`gcc_jit_result` instances created by the context will use the logfile. There may a performance cost for logging. You can turn off logging on `ctxt` by passing `NULL` for `logfile`. Doing so only affects the context; it does not affect child contexts or :c:type:`gcc_jit_result` instances already created by the context. The parameters "flags" and "verbosity" are reserved for future expansion, and must be zero for now. To contrast the above: :c:func:`gcc_jit_context_dump_to_file` dumps the current state of a context to the given path, whereas :c:func:`gcc_jit_context_set_logfile` enables on-going logging of future activies on a context to the given `FILE *`. .. function:: void\ gcc_jit_context_dump_reproducer_to_file (gcc_jit_context *ctxt,\ const char *path) Write C source code into `path` that can be compiled into a self-contained executable (i.e. with libgccjit as the only dependency). The generated code will attempt to replay the API calls that have been made into the given context. This may be useful when debugging the library or client code, for reducing a complicated recipe for reproducing a bug into a simpler form. For example, consider client code that parses some source file into some internal representation, and then walks this IR, calling into libgccjit. If this encounters a bug, a call to `gcc_jit_context_dump_reproducer_to_file` will write out C code for a much simpler executable that performs the equivalent calls into libgccjit, without needing the client code and its data. Typically you need to supply :option:`-Wno-unused-variable` when compiling the generated file (since the result of each API call is assigned to a unique variable within the generated C source, and not all are necessarily then used). .. function:: void\ gcc_jit_context_enable_dump (gcc_jit_context *ctxt,\ const char *dumpname, \ char **out_ptr) Enable the dumping of a specific set of internal state from the compilation, capturing the result in-memory as a buffer. Parameter "dumpname" corresponds to the equivalent gcc command-line option, without the "-fdump-" prefix. For example, to get the equivalent of :option:`-fdump-tree-vrp1`, supply ``"tree-vrp1"``: .. code-block:: c static char *dump_vrp1; void create_code (gcc_jit_context *ctxt) { gcc_jit_context_enable_dump (ctxt, "tree-vrp1", &dump_vrp1); /* (other API calls omitted for brevity) */ } The context directly stores the dumpname as a ``(const char *)``, so the passed string must outlive the context. :func:`gcc_jit_context_compile` will capture the dump as a dynamically-allocated buffer, writing it to ``*out_ptr``. The caller becomes responsible for calling: .. code-block:: c free (*out_ptr) each time that :func:`gcc_jit_context_compile` is called. ``*out_ptr`` will be written to, either with the address of a buffer, or with ``NULL`` if an error occurred. .. warning:: This API entrypoint is likely to be less stable than the others. In particular, both the precise dumpnames, and the format and content of the dumps are subject to change. It exists primarily for writing the library's own test suite. Options ------- Options present in the initial release of libgccjit were handled using enums, whereas those added subsequently have their own per-option API entrypoints. Adding entrypoints for each new option means that client code that use the new options can be identified directly from binary metadata, which would not be possible if we instead extended the various ``enum gcc_jit_*_option``. String Options ************** .. function:: void gcc_jit_context_set_str_option(gcc_jit_context *ctxt, \ enum gcc_jit_str_option opt, \ const char *value) Set a string option of the context. .. type:: enum gcc_jit_str_option The parameter ``value`` can be NULL. If non-NULL, the call takes a copy of the underlying string, so it is valid to pass in a pointer to an on-stack buffer. There is just one string option specified this way: .. macro:: GCC_JIT_STR_OPTION_PROGNAME The name of the program, for use as a prefix when printing error messages to stderr. If `NULL`, or default, "libgccjit.so" is used. Boolean options *************** .. function:: void gcc_jit_context_set_bool_option(gcc_jit_context *ctxt, \ enum gcc_jit_bool_option opt, \ int value) Set a boolean option of the context. Zero is "false" (the default), non-zero is "true". .. type:: enum gcc_jit_bool_option .. macro:: GCC_JIT_BOOL_OPTION_DEBUGINFO If true, :func:`gcc_jit_context_compile` will attempt to do the right thing so that if you attach a debugger to the process, it will be able to inspect variables and step through your code. Note that you can't step through code unless you set up source location information for the code (by creating and passing in :type:`gcc_jit_location` instances). .. macro:: GCC_JIT_BOOL_OPTION_DUMP_INITIAL_TREE If true, :func:`gcc_jit_context_compile` will dump its initial "tree" representation of your code to stderr (before any optimizations). Here's some sample output (from the `square` example):: > side-effects head 0x7f4875a761e0 tail 0x7f4875a761f8 stmts 0x7f4875a62d20 0x7f4875a62d00 stmt side-effects arg 0 VOID file (null) line 0 col 0 align 1 context >> stmt unit size align 32 symtab 0 alias set -1 canonical type 0x7f4875a645e8 precision 32 min max pointer_to_this > side-effects arg 0 side-effects arg 0 arg 1 arg 0 arg 1 >>>> .. macro:: GCC_JIT_BOOL_OPTION_DUMP_INITIAL_GIMPLE If true, :func:`gcc_jit_context_compile` will dump the "gimple" representation of your code to stderr, before any optimizations are performed. The dump resembles C code: .. code-block:: c square (signed int i) { signed int D.56; entry: D.56 = i * i; return D.56; } .. macro:: GCC_JIT_BOOL_OPTION_DUMP_GENERATED_CODE If true, :func:`gcc_jit_context_compile` will dump the final generated code to stderr, in the form of assembly language: .. code-block:: gas .file "fake.c" .text .globl square .type square, @function square: .LFB0: .cfi_startproc pushq %rbp .cfi_def_cfa_offset 16 .cfi_offset 6, -16 movq %rsp, %rbp .cfi_def_cfa_register 6 movl %edi, -4(%rbp) .L2: movl -4(%rbp), %eax imull -4(%rbp), %eax popq %rbp .cfi_def_cfa 7, 8 ret .cfi_endproc .LFE0: .size square, .-square .ident "GCC: (GNU) 4.9.0 20131023 (Red Hat 0.1-%{gcc_release})" .section .note.GNU-stack,"",@progbits .. macro:: GCC_JIT_BOOL_OPTION_DUMP_SUMMARY If true, :func:`gcc_jit_context_compile` will print information to stderr on the actions it is performing. .. macro:: GCC_JIT_BOOL_OPTION_DUMP_EVERYTHING If true, :func:`gcc_jit_context_compile` will dump copious amount of information on what it's doing to various files within a temporary directory. Use :macro:`GCC_JIT_BOOL_OPTION_KEEP_INTERMEDIATES` (see below) to see the results. The files are intended to be human-readable, but the exact files and their formats are subject to change. .. macro:: GCC_JIT_BOOL_OPTION_SELFCHECK_GC If true, libgccjit will aggressively run its garbage collector, to shake out bugs (greatly slowing down the compile). This is likely to only be of interest to developers *of* the library. It is used when running the selftest suite. .. macro:: GCC_JIT_BOOL_OPTION_KEEP_INTERMEDIATES If true, the :type:`gcc_jit_context` will not clean up intermediate files written to the filesystem, and will display their location on stderr. .. function:: void \ gcc_jit_context_set_bool_allow_unreachable_blocks (gcc_jit_context *ctxt, \ int bool_value) By default, libgccjit will issue an error about unreachable blocks within a function. This entrypoint can be used to disable that error. This entrypoint was added in :ref:`LIBGCCJIT_ABI_2`; you can test for its presence using .. code-block:: c #ifdef LIBGCCJIT_HAVE_gcc_jit_context_set_bool_allow_unreachable_blocks .. function:: void \ gcc_jit_context_set_bool_use_external_driver (gcc_jit_context *ctxt, \ int bool_value) libgccjit internally generates assembler, and uses "driver" code for converting it to other formats (e.g. shared libraries). By default, libgccjit will use an embedded copy of the driver code. This option can be used to instead invoke an external driver executable as a subprocess. This entrypoint was added in :ref:`LIBGCCJIT_ABI_5`; you can test for its presence using .. code-block:: c #ifdef LIBGCCJIT_HAVE_gcc_jit_context_set_bool_use_external_driver .. function:: void \ gcc_jit_context_set_bool_print_errors_to_stderr (gcc_jit_context *ctxt, \ int enabled) By default, libgccjit will print errors to stderr. This entrypoint can be used to disable the printing. This entrypoint was added in :ref:`LIBGCCJIT_ABI_23`; you can test for its presence using .. code-block:: c #ifdef LIBGCCJIT_HAVE_gcc_jit_context_set_bool_print_errors_to_stderr Integer options *************** .. function:: void gcc_jit_context_set_int_option (gcc_jit_context *ctxt, \ enum gcc_jit_int_option opt, \ int value) Set an integer option of the context. .. type:: enum gcc_jit_int_option There is just one integer option specified this way: .. macro:: GCC_JIT_INT_OPTION_OPTIMIZATION_LEVEL How much to optimize the code. Valid values are 0-3, corresponding to GCC's command-line options -O0 through -O3. The default value is 0 (unoptimized). Additional command-line options ******************************* .. function:: void gcc_jit_context_add_command_line_option (gcc_jit_context *ctxt,\ const char *optname) Add an arbitrary gcc command-line option to the context, for use by :func:`gcc_jit_context_compile` and :func:`gcc_jit_context_compile_to_file`. The parameter ``optname`` must be non-NULL. The underlying buffer is copied, so that it does not need to outlive the call. Extra options added by `gcc_jit_context_add_command_line_option` are applied *after* the regular options above, potentially overriding them. Options from parent contexts are inherited by child contexts; options from the parent are applied *before* those from the child. For example: .. code-block:: c gcc_jit_context_add_command_line_option (ctxt, "-ffast-math"); gcc_jit_context_add_command_line_option (ctxt, "-fverbose-asm"); Note that only some options are likely to be meaningful; there is no "frontend" within libgccjit, so typically only those affecting optimization and code-generation are likely to be useful. This entrypoint was added in :ref:`LIBGCCJIT_ABI_1`; you can test for its presence using .. code-block:: c #ifdef LIBGCCJIT_HAVE_gcc_jit_context_add_command_line_option .. function:: void gcc_jit_context_add_driver_option (gcc_jit_context *ctxt,\ const char *optname) Add an arbitrary gcc driver option to the context, for use by :func:`gcc_jit_context_compile` and :func:`gcc_jit_context_compile_to_file`. The parameter ``optname`` must be non-NULL. The underlying buffer is copied, so that it does not need to outlive the call. Extra options added by `gcc_jit_context_add_driver_option` are applied *after* all other options potentially overriding them. Options from parent contexts are inherited by child contexts; options from the parent are applied *before* those from the child. For example: .. code-block:: c gcc_jit_context_add_driver_option (ctxt, "-lm"); gcc_jit_context_add_driver_option (ctxt, "-fuse-linker-plugin"); gcc_jit_context_add_driver_option (ctxt, "obj.o"); gcc_jit_context_add_driver_option (ctxt, "-L."); gcc_jit_context_add_driver_option (ctxt, "-lwhatever"); Note that only some options are likely to be meaningful; there is no "frontend" within libgccjit, so typically only those affecting assembler and linker are likely to be useful. This entrypoint was added in :ref:`LIBGCCJIT_ABI_11`; you can test for its presence using .. code-block:: c #ifdef LIBGCCJIT_HAVE_gcc_jit_context_add_driver_option