[英]How do template instantiations get compiled by Clang?
I am using Clang as a library to compile some templated code: 我使用Clang作为库来编译一些模板化代码:
template<typename T>
T getSevenTemplated() {
return 7;
}
int getSeven() {
return getSevenTemplated<int>();
}
Unfortunately, the compiled LLVM IR does not actually contain the implementation of 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)"}
Here is the code I am using to generate the LLVM module: 这是我用来生成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());
To investigate why, I looked through the source-code and I found that the CodeGenerator
has specific logic for handling templates: it seems to skip function template instantiations! 为了研究原因,我查看了源代码 ,发现
CodeGenerator
具有处理模板的特定逻辑:它似乎跳过了函数模板实例化! I presume that it handles the generated functions instead, but I don't know how it really works. 我认为它处理生成的函数,但我不知道它是如何工作的。
My questions are: 我的问题是:
ASTConsumer
for code generation? ASTConsumer
以生成代码? The problem was that I had incremental parsing turned on. 问题是我打开了增量解析。 With this setting enabled, the
ParseAST
function does not call clang::Sema::ActOnEndOfTranslationUnit
, which triggers the instantiation of templates. 启用此设置后,
ParseAST
函数不会调用clang::Sema::ActOnEndOfTranslationUnit
,这会触发模板的实例化。
The trick is to add this call after processing your decls: 诀窍是在处理你的decl后添加这个调用:
// This triggers the instantiation of templated functions
sema.ActOnEndOfTranslationUnit();
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