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[flang] Document preprocessing more. 

Original-commit: flang-compiler/f18@93f7a0b011
Reviewed-on: https://github.com/flang-compiler/f18/pull/87
Tree-same-pre-rewrite: false
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peter klausler 2018-05-11 13:29:22 -07:00
parent f651e74244
commit 484a852cff
1 changed files with 19 additions and 5 deletions
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flang/documentation/preprocessing.md
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@ -85,13 +85,27 @@ In short, a Fortran preprocessor should work as if:
--------------------------------------------------- ---------------------------------------------------
1. Fixed form lines are padded up to column 72 (or 132) and clipped thereafter. 1. Fixed form lines are padded up to column 72 (or 132) and clipped thereafter.
2. Fortran comments are removed. 2. Fortran comments are removed.
3. Fortran line continuations are processed (outside directives). 3. C-style line continuations are processed in preprocessing directives.
4. C-style line continuations are processed in directives. 4. C old-style comments are removed from directives.
5. C old-style comments are removed from directives. 5. Fortran line continuations are processed (outside preprocessing directives).
6. Directives are processed and macros expanded. Line continuation rules depend on source form.
Comment lines that are enabled compiler directives have their line
continuations processed.
Conditional compilation preprocessing directives (e.g., `#if`) may be
appear among continuation lines, and have their usual effects upon them.
6. Other preprocessing directives are processed and macros expanded.
Along the way, Fortran `INCLUDE` lines and preprocessor `#include` directives Along the way, Fortran `INCLUDE` lines and preprocessor `#include` directives
are expanded, and all these steps applied recursively to the introduced text. are expanded, and all these steps applied recursively to the introduced text.
7. Newly visible Fortran comments are removed. 7. Any newly-created Fortran comments are removed.
Steps 5 and 6 are interleaved with respect to the preprocessing state.
Conditional compilation preprocessing directives always reflect only the macro
definition state produced by the active `#define` and `#undef` preprocessing directives
that precede them.
If the source form is changed by means of a compiler directive (i.e.,
`!DIR$ FIXED` or `FREE`) in an included source file, its effects cease
at the end of that file.
Last, if the preprocessor is not integrated into the Fortran compiler, Last, if the preprocessor is not integrated into the Fortran compiler,
new Fortran continuation line markers should be introduced into the final new Fortran continuation line markers should be introduced into the final