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| author | Sebastian Redl <sebastian.redl@getdesigned.at> | 2010-07-08 22:01:51 +0000 |
|---|---|---|
| committer | Sebastian Redl <sebastian.redl@getdesigned.at> | 2010-07-08 22:01:51 +0000 |
| commit | a93e3b5bde9f0a7b59215f19f176f7d69881b81c (patch) | |
| tree | 8370d623fa21547d38f09c84df7b6559531f8f91 /docs/PCHInternals.html | |
| parent | 80db8cbff5afc047a23dbfe11f7ef787d891feec (diff) | |
Some preparatory work for chained PCH. No functionality change.
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@107915 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'docs/PCHInternals.html')
| -rw-r--r-- | docs/PCHInternals.html | 30 |
1 files changed, 30 insertions, 0 deletions
diff --git a/docs/PCHInternals.html b/docs/PCHInternals.html index e21ec5e90d..109d5ed025 100644 --- a/docs/PCHInternals.html +++ b/docs/PCHInternals.html @@ -144,6 +144,15 @@ deserialized from the precompiled header. These statistics can be useful to determine whether the precompiled header implementation can be improved by making more of the implementation lazy.</p> +<p>Precompiled headers can be chained. When you create a PCH while +including an existing PCH, Clang can create the new PCH by referencing +the original file and only writing the new data to the new file. For +example, you could create a PCH out of all the headers that are very +commonly used throughout your project, and then create a PCH for every +single source file in the project that includes the code that is +specific to that file, so that recompiling the file itself is very fast, +without duplicating the data from the common headers for every file.</p> + <h2 id="contents">Precompiled Header Contents</h2> <img src="PCHLayout.png" align="right" alt="Precompiled header layout"> @@ -209,6 +218,27 @@ contents are verified along with the rest of the metadata.</dd> </dl> +<p>A chained PCH file (that is, one that references another PCH) has +a slightly different metadata block, which contains the following +information:</p> + +<dl> + <dt>Referenced file</dt> + <dd>The name of the referenced PCH file. It is looked up like a file +specified using -include-pch.</dd> + + <dt>PCH version</dt> + <dd>This is the same as in normal PCH files.</dd> + + <dt>Original file name</dt> + <dd>The full path of the header that was used to generate this +precompiled header.</dd> + +</dl> + +<p>The language options, target architecture and predefines buffer data +is taken from the end of the chain, since they have to match anyway.</p> + <h3 id="sourcemgr">Source Manager Block</h3> <p>The source manager block contains the serialized representation of |