forked from OSchip/llvm-project
7d23857a07
Stat'ing all the headers from the PCH to make sure they are up-to-date takes significant time.
In a particular source file (whose PCH file included Cocoa.h) from total -fsyntax-only time
12% was just stat calls. Change pre-validation to only check non-system headers.
There are some notable disadvantages:
-If a system header, that is not include-guarded, changes after the PCH was created, we will not
find it in the header info table and we will #import it, effectively #importing it twice, thus
we will emit some error due to a multiple definition and after that the "header was modified" error will likely
be emitted, for example something like:
NSDictionary.h:12:1: error: duplicate interface definition for class 'NSDictionary'
@interface NSDictionary : NSObject <NSCopying, NSMutableCopying, NSSecureCoding, NSFastEnumeration>
^
NSDictionary.h:12:12: note: previous definition is here
@interface NSDictionary : NSObject <NSCopying, NSMutableCopying, NSSecureCoding, NSFastEnumeration>
^
fatal error: file 'NSDictionary.h' has been modified since the precompiled header was built
Though we get the "header was modified" error, this is a bit confusing.
-Theoretically it is possible that such a system header will cause no errors but it will just cause an
unfortunate semantic change, though I find this rather unlikely.
The advantages:
-Reduces compilation time when using a huge PCH like the Cocoa ones
-System headers change very infrequent and when they do, users/build systems should be able to know that
re-building from scratch is needed.
Addresses rdar://13056262
llvm-svn: 176567
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| .. | ||
| ASTCommon.cpp | ||
| ASTCommon.h | ||
| ASTReader.cpp | ||
| ASTReaderDecl.cpp | ||
| ASTReaderInternals.h | ||
| ASTReaderStmt.cpp | ||
| ASTWriter.cpp | ||
| ASTWriterDecl.cpp | ||
| ASTWriterStmt.cpp | ||
| CMakeLists.txt | ||
| GeneratePCH.cpp | ||
| GlobalModuleIndex.cpp | ||
| Makefile | ||
| Module.cpp | ||
| ModuleManager.cpp | ||