Hi All,
Recently I am using clang++ (3.8.0) to compile some c++ programs and find that some type names will be changed after linking different modules. Here is a simple example:
I have two files: main.cpp and b.cpp
main.cpp
#include
using namespace std;
class A {
public:
virtual void f() {
cout << “A:\tf\n”;
}
};
int main ()
{
A *p = new A;
p->f();
return 0;
}
b.cpp
#include
using namespace std;
class X {
public:
virtual int g();
};
int X::g()
{
cout << “X:\tg\n”;
return 0;
}
I use the following commands to compile these two files separately and then link them tegother:
clang++ -c -emit-llvm -o b.bc b.cpp
clang++ -c -emit-llvm -o main.bc main.cpp
llvm-link -o whole.bc b.bc main.bc
opt -mem2reg -o whole.mem2reg.bc whole.bc
llvm-dis -o whole.mem2reg.ll whole.mem2reg.bc
In the file whole.mem2reg.ll, type “class.A” has been replaced by “class.X” in function main, the constructor of class A and the virtual member function f of class A:
; Function Attrs: norecurse uwtable
define i32 @main() #3 {
%1 = call noalias i8* @_Znwm(i64 8) #6
%2 = bitcast i8* %1 to %class.X*
call void @_ZN1AC2Ev(%class.X* %2) #2
%3 = bitcast %class.X* %2 to void (%class.X*)***
%4 = load void (%class.X*), void (%class.X*)* %3, align 8
%5 = getelementptr inbounds void (%class.X*), void (%class.X)** %4, i64 0
%6 = load void (%class.X*), void (%class.X)** %5, align 8
call void %6(%class.X* %2)
ret i32 0
}
; Function Attrs: inlinehint nounwind uwtable
define linkonce_odr void @_ZN1AC2Ev(%class.X* %this) unnamed_addr #5 comdat align 2 {
%1 = bitcast %class.X* %this to i32 (…)***
store i32 (…)** bitcast (i8** getelementptr inbounds ([3 x i8*], [3 x i8*]* @_ZTV1A, i64 0, i64 2) to i32 (…)), i32 (…)* %1, align 8
ret void
}
; Function Attrs: uwtable
define linkonce_odr void @_ZN1A1fEv(%class.X* %this) unnamed_addr #0 comdat align 2 {
%1 = call dereferenceable(272) %“class.std::basic_ostream”* @_ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_PKc(%“class.std::basic_ostream”* dereferenceable(272) @_ZSt4cout, i8* getelementptr inbounds ([6 x i8], [6 x i8]* @.str.4, i32 0, i32 0))
ret void
}
Does anyone know why llvm replace the type name and how to stop llvm from doing this?
Thanks