[LLVMdev] How do I find all memory allocations in an llvm ir codefile?

[James Molloy]

Hi,

_Znwj and friends are the C++-name-mangled versions of operator new. Because operator new is so common, the IA64 C++ ABI provided a shorthand for it.

It can be parsed as follows:

_Z: Prefix to all c++ mangled names.
nw: operator new(). The other version is "na": operator new[](). ("na"->new array).
j: unsigned int.

All of these can be found in the C++ ABI: http://www.codesourcery.com/public/cxx-abi/abi.html#mangling

You can run an identifier through the g++ tool "c++filt" to get a human-readable representation:

$ c++filt _Znwj
operator new(unsigned int)

Cheers,

James

> -----Original Message-----
> From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu]
> On Behalf Of Theresia Hansson
> Sent: 15 October 2010 12:38
> To: llvmdev at cs.uiuc.edu
> Subject: [LLVMdev] How do I find all memory allocations in an llvm ir
> codefile?
> 
> I tried to compile this snippet of C++ code:
> 
> void FuncTest() {
>     int* a = new int;
>     int* b = new int[2];
> }
> 
> using:
> 
> clang test.cpp -S -emit-llvm -o - > test.llvm
> 
> and obtained this:
> 
> define void @_Z8FuncTestv() {
> entry:
>   %a = alloca i32*, align 4
>   %b = alloca i32*, align 4
>   %call = call noalias i8* @_Znwj(i32 4)
>   %0 = bitcast i8* %call to i32*
>   store i32* %0, i32** %a, align 4
>   %call1 = call noalias i8* @_Znaj(i32 8)
>   %1 = bitcast i8* %call1 to i32*
>   store i32* %1, i32** %b, align 4
>   ret void
> }
> 
> declare noalias i8* @_Znwj(i32)
> declare noalias i8* @_Znaj(i32)
> 
> What I am wondering now is: where do the _Znwj and _Znaj symbols come
> from? Are they just randomly assigned or is there a system to it? I
> would like to be able to tell that the lines
> 
> %call = call noalias i8* @_Znwj(i32 4)
> 
> and
> 
> %call1 = call noalias i8* @_Znaj(i32 8)
> 
> perform memory allocations. But it does not look that promising...
> Some llvm expert here who has an idea?
> 
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