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Diffstat (limited to 'clang')
| -rw-r--r-- | clang/docs/PTHInternals.html | 27 |
1 files changed, 17 insertions, 10 deletions
diff --git a/clang/docs/PTHInternals.html b/clang/docs/PTHInternals.html index 955699d9d42..3f0927338f9 100644 --- a/clang/docs/PTHInternals.html +++ b/clang/docs/PTHInternals.html @@ -131,11 +131,12 @@ of header files. The current implementation of PCH in Clang as pretokenized header files was motivated by the following factors:<p> <ul> -<li><p><em>Language independence</em>: PTH files are (roughly) language -independent. They work with any language that Clang's lexer can handle, -including C, Objective-C, and (in the early stages) C++. This means development -on language features at the parsing level or above (which is basically almost -all interesting pieces) does not require PTH to be modified.</p></li> + +<li><p><em>Language independence</em>: PTH files work with any language that +Clang's lexer can handle, including C, Objective-C, and (in the early stages) +C++. This means development on language features at the parsing level or above +(which is basically almost all interesting pieces) does not require PTH to be +modified.</p></li> <li><em>Simple design</em>: Relatively speaking, PTH has a simple design and implementation, making it easy to test. Further, because the machinery for PTH @@ -172,6 +173,12 @@ also modifies those pages in memory, incurring the copy-on-write costs. The read-only nature of PTH can greatly reduce memory pressure for builds involving multiple cores, thus improving overall scalability.</p></li> +<li><p><em>Fast generation<em>: PTH files can be generated in a small fraction +of the time needed to generate GCC's PCH files. Since PTH/PCH generation is a +serial operation that typically blocks progress during a build, faster +generation time leads to improved processor utilization with parallel builds on +multicore machines.</p></li> + </ul> <p>Despite these strengths, PTH's simple design suffers some algorithmic @@ -188,11 +195,11 @@ strengths via the use of copy-on-write pages, the approach itself can fundamentally dominate at an algorithmic level, especially when one considers header files of arbitrary size.</p> -<p>Consequently, as alluded earlier, there are plans to potentially implement an -alternative PCH implementation for Clang based on the lazy deserialization of -ASTs. This approach would theoretically have the same constant-time algorithmic -advantages just mentioned but would also retain some of the strengths of PTH -such as reduced memory pressure (ideal for multi-core builds).</p> +<p>There are plans to potentially implement an complementary PCH implementation +for Clang based on the lazy deserialization of ASTs. This approach would +theoretically have the same constant-time algorithmic advantages just mentioned +but would also retain some of the strengths of PTH such as reduced memory +pressure (ideal for multi-core builds).</p> <h3>Internal PTH Optimizations</h3> |
