LLVM新建全局变量

在LLVM中,有原生的AST Clone,却没有一个比较好的Stmt copy功能,基于Scout在LLVM上进行的修改,我们实现了自己的Stmt Clone功能。

要进行Stmt Clone,肯定需要新建新的AST节点,首先用一个立即介绍如何进行AST节点的构建,以新建一个全局的variable为例。

首先分析下需求,新建variable,自然的有几个问题:

1.变量如何新建

2.新建的变量应该处于程序的哪个部分

以如下的代码为例子:

int main()
{
  return 0;
}

我们有两个地方可以插入新建的variable,一个是将其作为全局变量进行插入,一个是作为main函数的局部变量进行插入,这里选择作为全局变量进行插入。那么插入后,示例代码会变成:

int main()
{
  return 0;
}
int a;

(想要有个比较系统的了解的,建议看下tools/clang/lib/StaticAnalyzer,StaticAnalyzer是一个良好的例子)

std::string keyName = "a";
int value = 0;

IdentifierTable& idTable = Context->Idents;
IdentifierInfo&  idInfo =idTable.get(keyName);
const SourceLocation nopos;
    VarDecl *tmpVar = VarDecl::Create(*Context, Context->getTranslationUnitDecl(), nopos, nopos, &idInfo, Context->IntTy, Context->CreateTypeSourceInfo(Context->IntTy), SC_None);
Context->getTranslationUnitDecl()->addDeclInternal (tmpVar);
IntegerLiteral *init = IntegerLiteral::Create(*Context,llvm::APInt(Context->getIntWidth(Context->IntTy),value,true),
        Context->IntTy,nopos);
 if (init != 0)
 {
    tmpVar->setInit(init);
 }

如果想新建一个int *a;这种的,稍微比较麻烦,因为需要自己新建类型。在context中只提供了基础类型的:

  // Builtin Types.
  CanQualType VoidTy;
  CanQualType BoolTy;
  CanQualType CharTy;
  CanQualType WCharTy;  // [C++ 3.9.1p5].
  CanQualType WideCharTy; // Same as WCharTy in C++, integer type in C99.
  CanQualType WIntTy;   // [C99 7.24.1], integer type unchanged by default promotions.
  CanQualType Char16Ty; // [C++0x 3.9.1p5], integer type in C99.
  CanQualType Char32Ty; // [C++0x 3.9.1p5], integer type in C99.
  CanQualType SignedCharTy, ShortTy, IntTy, LongTy, LongLongTy, Int128Ty;
  CanQualType UnsignedCharTy, UnsignedShortTy, UnsignedIntTy, UnsignedLongTy;
  CanQualType UnsignedLongLongTy, UnsignedInt128Ty;
  CanQualType FloatTy, DoubleTy, LongDoubleTy, Float128Ty;
  CanQualType HalfTy; // [OpenCL 6.1.1.1], ARM NEON
  CanQualType FloatComplexTy, DoubleComplexTy, LongDoubleComplexTy;
  CanQualType Float128ComplexTy;
  CanQualType VoidPtrTy, NullPtrTy;
  CanQualType DependentTy, OverloadTy, BoundMemberTy, UnknownAnyTy;
  CanQualType BuiltinFnTy;
  CanQualType PseudoObjectTy, ARCUnbridgedCastTy;
  CanQualType ObjCBuiltinIdTy, ObjCBuiltinClassTy, ObjCBuiltinSelTy;
  CanQualType ObjCBuiltinBoolTy;
#define IMAGE_TYPE(ImgType, Id, SingletonId, Access, Suffix) \
  CanQualType SingletonId;
#include "clang/Basic/OpenCLImageTypes.def"
  CanQualType OCLSamplerTy, OCLEventTy, OCLClkEventTy;
  CanQualType OCLQueueTy, OCLNDRangeTy, OCLReserveIDTy;
  CanQualType OMPArraySectionTy;

  // Types for deductions in C++0x [stmt.ranged]'s desugaring. Built on demand.
  mutable QualType AutoDeductTy;     // Deduction against 'auto'.
  mutable QualType AutoRRefDeductTy; // Deduction against 'auto &&'.

  // Decl used to help define __builtin_va_list for some targets.
  // The decl is built when constructing 'BuiltinVaListDecl'.
  mutable Decl *VaListTagDecl;

新建int *a;第一步自然是在源码中手动插入这样的代码,使用clang -fsyntax-only -Xclang -ast-dump test.cpp来查看这个新建的AST节点是如何表达的,再寻找对应的新建方式。

VarDecl 0xccec418 <test.cpp:2:1, col:6> col:6 a 'int *'

经过查找,我们发现,假如我们在遍历AST树根节点的子节点的时候,添加如下的处理代码:

else if(isa<VarDecl>(*D))
    {
        VarDecl *var = dyn_cast<VarDecl>(*D);
        var->dump();
        QualType varTp = var->getType();
        
        while (true) {
            varTp.dump();
            const PointerType *pointTp = varTp->getAs<PointerType>();
            if(pointTp==NULL)
            {
                const Type* ET = varTp->getArrayElementTypeNoTypeQual();
                ET->dump();
                break;
            }
            varTp = pointTp ->getPointeeType();
            
        }
        std::cout <<"********"<<std::endl;
    }

输出的代码如下:

VarDecl 0xde9dcf0 <test.cpp:2:1, col:6> col:6 a 'int *'
PointerType 0xd732d00 'int *'
`-BuiltinType 0xd6a8140 'int' 
BuiltinType 0xd6a8140 'int' 
<<<NULL>>>
********

这里就比较明显了,这个VarDecl的QUALType是 PointerType,而PointerType对应的Pointee是int。

这样模仿上边的代码,如果新建一个int **aaaa;的节点,可以使用:

std::string keyName = "aaaa";
IdentifierTable& idTable = Context->Idents;
IdentifierInfo&  idInfo =idTable.get(keyName);
const SourceLocation nopos;
QualType PointerTy_1 = Context->getPointerType(Context->getIntTypeForBitwidth(32, 1));
QualType PointerTy_2 = Context->getPointerType(PointerTy_1);
VarDecl *tmpVar = VarDecl::Create(*Context, Context->getTranslationUnitDecl(), nopos, nopos, &idInfo, PointerTy_2, Context->CreateTypeSourceInfo(PointerTy_2), SC_None);
Context->getTranslationUnitDecl()->addDecl (tmpVar);

 

本来想写Stmt Clone的,太多了,不好讲,先鸽。

posted @ 2019-05-05 16:42  转换无极限  阅读(1338)  评论(0编辑  收藏  举报