Add PCH for Sema Structure#1
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Extends the PCH infrastructure (already there for LLVMSupport, LLVMCore, LLVMCodeGen, clangAST) to clangSema, which was the largest remaining gap. clangSema (clang/include/clang/Sema/pch.h): - Builds on clang/AST/pch.h (inheriting ASTContext, Expr, Decl, etc.) - Adds the 8 most commonly included Sema-specific headers across the 86 .cpp files in clang/lib/Sema/: Sema.h (698KB/15690 lines, 36 TUs), Lookup.h (30 TUs), Initialization.h (31 TUs), ScopeInfo.h (26 TUs), Scope.h (20 TUs), DiagnosticSema.h (26 TUs), TargetInfo.h (34 TUs), Preprocessor.h (25 TUs)
LLVM_OPTIMIZED_TABLEGEN defaults to OFF but the docs recommend enabling it for Release builds to avoid a slow debug-mode llvm-tblgen bottlenecking the rest of the build. The X86 target alone generates 18 .inc files (X86GenDAGISel.inc, X86GenAsmMatcher.inc, etc.) which are all on the critical path — no X86 source file can start compiling until they finish. Auto-enable LLVM_OPTIMIZED_TABLEGEN when: - Not cross-compiling (host tools are already used when cross-compiling) - CMAKE_BUILD_TYPE is Release or RelWithDebInfo - The user has not explicitly set LLVM_OPTIMIZED_TABLEGEN Users who want the old behaviour can pass -DLLVM_OPTIMIZED_TABLEGEN=OFF
Split SemaExpr.cpp (877 KB, ~22K lines) at the natural section boundary of the "Clang Extensions" block (blocks, __unknown_anytype, typeof, __builtin_choose_expr, etc.) into a separate translation unit SemaExprExtensions.cpp (~5,200 lines). The RebuildUnknownAnyFunction struct and its wrapper function were relocated from the extensions section to the main file before their first call site, to preserve internal linkage semantics. This allows clangSema to compile SemaExpr.cpp and SemaExprExtensions.cpp in parallel, reducing the build bottleneck from this single large TU.
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Added support for PCH for clang Sema