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| Next: <a href="Cilk-Plus-Transformation.html#Cilk-Plus-Transformation" accesskey="n" rel="next">Cilk Plus Transformation</a>, Up: <a href="Passes.html#Passes" accesskey="u" rel="up">Passes</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p> |
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| <a name="Parsing-pass-1"></a> |
| <h3 class="section">9.1 Parsing pass</h3> |
| <a name="index-GENERIC"></a> |
| <a name="index-lang_005fhooks_002eparse_005ffile"></a> |
| <p>The language front end is invoked only once, via |
| <code>lang_hooks.parse_file</code>, to parse the entire input. The language |
| front end may use any intermediate language representation deemed |
| appropriate. The C front end uses GENERIC trees (see <a href="GENERIC.html#GENERIC">GENERIC</a>), plus |
| a double handful of language specific tree codes defined in |
| <samp>c-common.def</samp>. The Fortran front end uses a completely different |
| private representation. |
| </p> |
| <a name="index-GIMPLE"></a> |
| <a name="index-gimplification"></a> |
| <a name="index-gimplifier"></a> |
| <a name="index-language_002dindependent-intermediate-representation"></a> |
| <a name="index-intermediate-representation-lowering"></a> |
| <a name="index-lowering_002c-language_002ddependent-intermediate-representation"></a> |
| <p>At some point the front end must translate the representation used in the |
| front end to a representation understood by the language-independent |
| portions of the compiler. Current practice takes one of two forms. |
| The C front end manually invokes the gimplifier (see <a href="GIMPLE.html#GIMPLE">GIMPLE</a>) on each function, |
| and uses the gimplifier callbacks to convert the language-specific tree |
| nodes directly to GIMPLE before passing the function off to be compiled. |
| The Fortran front end converts from a private representation to GENERIC, |
| which is later lowered to GIMPLE when the function is compiled. Which |
| route to choose probably depends on how well GENERIC (plus extensions) |
| can be made to match up with the source language and necessary parsing |
| data structures. |
| </p> |
| <p>BUG: Gimplification must occur before nested function lowering, |
| and nested function lowering must be done by the front end before |
| passing the data off to cgraph. |
| </p> |
| <p>TODO: Cgraph should control nested function lowering. It would |
| only be invoked when it is certain that the outer-most function |
| is used. |
| </p> |
| <p>TODO: Cgraph needs a gimplify_function callback. It should be |
| invoked when (1) it is certain that the function is used, (2) |
| warning flags specified by the user require some amount of |
| compilation in order to honor, (3) the language indicates that |
| semantic analysis is not complete until gimplification occurs. |
| Hum… this sounds overly complicated. Perhaps we should just |
| have the front end gimplify always; in most cases it’s only one |
| function call. |
| </p> |
| <p>The front end needs to pass all function definitions and top level |
| declarations off to the middle-end so that they can be compiled and |
| emitted to the object file. For a simple procedural language, it is |
| usually most convenient to do this as each top level declaration or |
| definition is seen. There is also a distinction to be made between |
| generating functional code and generating complete debug information. |
| The only thing that is absolutely required for functional code is that |
| function and data <em>definitions</em> be passed to the middle-end. For |
| complete debug information, function, data and type declarations |
| should all be passed as well. |
| </p> |
| <a name="index-rest_005fof_005fdecl_005fcompilation"></a> |
| <a name="index-rest_005fof_005ftype_005fcompilation"></a> |
| <a name="index-cgraph_005ffinalize_005ffunction"></a> |
| <p>In any case, the front end needs each complete top-level function or |
| data declaration, and each data definition should be passed to |
| <code>rest_of_decl_compilation</code>. Each complete type definition should |
| be passed to <code>rest_of_type_compilation</code>. Each function definition |
| should be passed to <code>cgraph_finalize_function</code>. |
| </p> |
| <p>TODO: I know rest_of_compilation currently has all sorts of |
| RTL generation semantics. I plan to move all code generation |
| bits (both Tree and RTL) to compile_function. Should we hide |
| cgraph from the front ends and move back to rest_of_compilation |
| as the official interface? Possibly we should rename all three |
| interfaces such that the names match in some meaningful way and |
| that is more descriptive than "rest_of". |
| </p> |
| <p>The middle-end will, at its option, emit the function and data |
| definitions immediately or queue them for later processing. |
| </p> |
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