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最近我用LLVM API来测试C++程序。现在我想找出不同功能之间的共享变量,有没有办法做到这一点?看起来AliasAnalysis不起作用!如何使用LLVM API在函数中找出共享变量?
我写一个函数传递如下:
bool EscapeAnalysis::runOnFunction(Function& F) {
EscapePoints.clear();
TargetData& TD = getAnalysis<TargetData>();
AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
Module* M = F.getParent();
// errs() << *M << "\n";
// Walk through all instructions in the function, identifying those that
// may allow their inputs to escape.
for(inst_iterator II = inst_begin(F), IE = inst_end(F); II != IE; ++II) {
Instruction* I = &*II;
// The most obvious case is stores. Any store that may write to global
// memory or to a function argument potentially allows its input to escape.
if (StoreInst* S = dyn_cast<StoreInst>(I)) {
Type* StoreType = S->getOperand(0)->getType();
unsigned StoreSize = TD.getTypeStoreSize(StoreType);
Value* Pointer = S->getPointerOperand();
bool inserted = false;
for (Function::arg_iterator AI = F.arg_begin(), AE = F.arg_end();
AI != AE; ++AI) {
if (!isa<PointerType>(AI->getType())) continue;
AliasAnalysis::AliasResult R = AA.alias(Pointer, StoreSize, AI, ~0UL);
if (R != AliasAnalysis::NoAlias) {
EscapePoints.insert(S);
inserted = true;
break;
}
}
if (inserted)
continue;
for (Module::global_iterator GI = M->global_begin(), GE = M->global_end();
GI != GE; ++GI) {
errs() << *GI << "\n";
AliasAnalysis::AliasResult R = AA.alias(Pointer, StoreSize, GI, ~0UL);
errs() << "R: " << R << " , NoAlias: " << AliasAnalysis::NoAlias << "\n";
if (R != AliasAnalysis::NoAlias) {
EscapePoints.insert(S);
break;
}
}
// Calls and invokes potentially allow their parameters to escape.
// FIXME: This can and should be refined. Intrinsics have known escape
// behavior, and alias analysis may be able to tell us more about callees.
} else if (isa<CallInst>(I) || isa<InvokeInst>(I)) {
EscapePoints.insert(I);
// Returns allow the return value to escape. This is mostly important
// for malloc to alloca promotion.
} else if (isa<ReturnInst>(I)) {
EscapePoints.insert(I);
// Branching on the value of a pointer may allow the value to escape through
// methods not discoverable via def-use chaining.
} else if(isa<BranchInst>(I) || isa<SwitchInst>(I)) {
EscapePoints.insert(I);
}
// FIXME: Are there any other possible escape points?
}
return false;
}
测试的main.cpp如下: 的#include
using namespace std;
int X = 0;
int foo() {
X = 1;
int b = 1;
return 0;
}
int bar(int param) {
int y = X;
int z = 9;
int a = z;
++a;
return 0;
}
int main(int argc, char *argv[])
{
cout << "Hello world!" << endl;
return 0;
}
全局变量X共享功能栏和功能foo之间的变量。 但是,当我使用命令如下运行通:
opt -load ./EscapeAnalysis.so -escape-analysis main.o | llc > main.ss
我得到的结果是:
R: 1 , NoAlias: 0
所有的结果都是一样的。 我打印出escapePoint中的变量,在函数栏中找到变量a,z,y在escapePoint中。这是不对的!
注:我写了一个选择通过测试程序。
你能准确地展示你如何使用别名分析吗?另外,你是否在寻找一种方法来查找共享*变量*(不需要别名分析)或共享*内存*(它确实)? – Oak
我已经向您展示了我如何使用别名分析,您可以检查它。哦,是的!你是否认为没有必要使用别名分析来查找共享变量?我想找出函数之间的共享变量。例如上面的函数栏和函数foo之间的变量X!但现在我不熟悉LLVM API,不知道该怎么做。 – ZZB