Clang如何实现模板实例化？
我使用Clang作为库来编译一些模板代码：
template<typename T>
T getSevenTemplated() {
return 7;
}
int getSeven() {
return getSevenTemplated<int>();
}
不幸的是，编译的LLVM IR实际上并不包含getSevenTemplated<int> ：
; ModuleID = './test.cpp'
source_filename = "./test.cpp"
target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-apple-macosx10.12.0"
; Function Attrs: ssp uwtable
define i32 @_Z8getSevenv() #0 {
entry:
%call = call i32 @_Z17getSevenTemplatedIiET_v()
ret i32 %call
}
declare i32 @_Z17getSevenTemplatedIiET_v() #1
attributes #0 = { ssp uwtable "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="penryn" "target-features"="+cx16,+fxsr,+mmx,+sse,+sse2,+sse3,+sse4.1,+ssse3,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
attributes #1 = { "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="penryn" "target-features"="+cx16,+fxsr,+mmx,+sse,+sse2,+sse3,+sse4.1,+ssse3,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
!llvm.module.flags = !{!0}
!llvm.ident = !{!1}
!0 = !{i32 1, !"PIC Level", i32 2}
!1 = !{!"clang version 5.0.0 (trunk 292778)"}
以下是我用来生成LLVM模块的代码：
auto* context = new llvm::LLVMContext(); // TODO: Fix leak
auto codeGenerator =
std::shared_ptr<clang::CodeGenerator>(
clang::CreateLLVMCodeGen(
compilerInstance.getDiagnostics(),
filePath,
compilerInstance.getHeaderSearchOpts(),
preprocessor.getPreprocessorOpts(),
compilerInstance.getCodeGenOpts(),
*context,
nullptr));
codeGenerator->Initialize(compilerInstance.getASTContext());
// declGroups are found by calling ParseAST with a special ASTConsumer earlier
for (auto declGroup : declGroups) {
codeGenerator->HandleTopLevelDecl(declGroup);
}
codeGenerator->HandleTranslationUnit(compilerInstance.getASTContext());
为了调查为什么，我查看了源代码，发现CodeGenerator具有处理模板的特定逻辑：它似乎忽略了函数模板实例化！ 我认为它处理生成的函数，但我不知道它是如何工作的。
我的问题是：
ASTConsumer进行代码生成？ 问题是我开启了增量分析。 启用此设置后， ParseAST函数不会调用clang::Sema::ActOnEndOfTranslationUnit ，它会触发模板的实例化。
诀窍是在处理你的decls后添加这个调用：
// This triggers the instantiation of templated functions
sema.ActOnEndOfTranslationUnit();