[clang] 6a6f10f - [Docs] [HLSL] Add note about PCH support

[Xiang Li via cfe-commits]

Author: Xiang Li
Date: 2022-10-07T10:49:21-07:00
New Revision: 6a6f10fd23b2730e2c01051541c5a83f5df9131b

URL: https://github.com/llvm/llvm-project/commit/6a6f10fd23b2730e2c01051541c5a83f5df9131b
DIFF: https://github.com/llvm/llvm-project/commit/6a6f10fd23b2730e2c01051541c5a83f5df9131b.diff

LOG: [Docs] [HLSL] Add note about PCH support

PCH supported for HLSL is added when compile in -cc1 mode using -include-pch for test AST.
This change add some notes about the support of PCH for HLSL.

Reviewed By: beanz

Differential Revision: https://reviews.llvm.org/D134330

Added: 
    

Modified: 
    clang/docs/HLSL/HLSLSupport.rst

Removed: 
    


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diff  --git a/clang/docs/HLSL/HLSLSupport.rst b/clang/docs/HLSL/HLSLSupport.rst
index a8c9c09b2e9f8..b091c17fd2a76 100644
--- a/clang/docs/HLSL/HLSLSupport.rst
+++ b/clang/docs/HLSL/HLSLSupport.rst
@@ -89,6 +89,15 @@ types and built-in templates. Clang is already designed to allow an attached
 ``ExternalSemaSource`` to lazily complete data types, which is a **huge**
 performance win for HLSL.
 
+If precompiled headers are used when compiling HLSL, the ``ExternalSemaSource``
+will be a ``MultiplexExternalSemaSource`` which includes both the ``ASTReader``
+and ``HLSLExternalSemaSource``. For Built-in declarations that are already
+completed in the serialized AST, the ``HLSLExternalSemaSource`` will reuse the
+existing declarations and not introduce new declarations. If the built-in types
+are not completed in the serialized AST, the ``HLSLExternalSemaSource`` will
+create new declarations and connect the de-serialized decls as the previous
+declaration.
+
 CodeGen
 -------