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

[Theresia Hansson]

Ah ok, thank you for that. I guess I was simply confused by the fact
that I got two different (to me they seemed randomly named) new
functions. Had I tried some more allocations I would probably had
noticed this, my bad :). Again thank you very much.

2010/10/15 John Criswell <criswell at illinois.edu>:
>  As others have mentioned, C++ mangles names (i.e., it changes the name of a
> symbol into a string that contains both the name, scope, and type of the
> variable or function), so if you know what the mangled name is of your
> allocator, you can recognize it.
>
> Additionally, I believe that functions with return values marked with the
> noalias attribute are, essentially, memory allocators because the return
> value is guaranteed to not alias with anything not based off of the return
> value.  See http://llvm.org/docs/LangRef.html#pointeraliasing for more
> details.
>
> As an aside, I've been thinking for awhile that we should have a "memory
> allocator" analysis group that identifies different allocators for different
> source-level languages (i.e., one analysis would recognize malloc, free,
> realloc, calloc while another would recognize new, new[], delete, and
> delete[]).  There are even analyses you can do to determine if a function is
> a memory allocator.  I have not yet had enough time to implement such an
> analysis group, but if others think it's a good idea, feel free to write it.
> :)
>
> -- John T.
>
> On 10/15/10 6:37 AM, Theresia Hansson wrote:
>>
>> 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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>
>