llvm dev - Oct 2015 - strdup vs __strdup?

Hello,

For background, I'm writing a pass and would like to find all 
instructions that could allocate memory, but this question mainly 
concerns strdup.

I'm seeing that calls to strdup are getting replaced by calls to 
__strdup when I compile with -O2.  Can anyone tell me why and what the 
difference is?

The replacement is a minor issue for me because isAllocationFn doesn't 
return true for calls to __strdup (but it does for strdup). My current 
workaround is to check the name of every called function.

Also, if there are any other functions that are replaced (like strdup is 
with __strdup), that'd be useful information to me.

My test case is [1].  I'm getting the bitcode using Module.print inside 
my pass. [2] is without -O2 and [3] is with -O2.  My pass is in CodeGen 
in case that is relevant.

Thanks,
Scott

[1] http://pastebin.com/LedrcAE3
[2] http://pastebin.com/3hkgNu60
[3] http://pastebin.com/uS0uD0Lk

Maybe this has been asked before but it's difficult to Google :)

Hi Scott,

On Wed, Oct 14, 2015 at 3:04 PM, carr27 via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> For background, I'm writing a pass and would like to find all
instructions
> that could allocate memory, but this question mainly concerns strdup.
>
> I'm seeing that calls to strdup are getting replaced by calls to
__strdup
> when I compile with -O2.  Can anyone tell me why and what the difference
is?
>
> The replacement is a minor issue for me because isAllocationFn doesn't
> return true for calls to __strdup (but it does for strdup). My current
> workaround is to check the name of every called function.
>
> Also, if there are any other functions that are replaced (like strdup is
> with __strdup), that'd be useful information to me.
>
> My test case is [1].  I'm getting the bitcode using Module.print inside
my
> pass. [2] is without -O2 and [3] is with -O2.  My pass is in CodeGen in
case
> that is relevant.
I don't think it's LLVM that's replacing the strdup call with
__strdup, but the header files in your standard library.

On my machine, /usr/include/string.h includes
/usr/include/x86_64-linux-gnu/bits/string2.h when __OPTIMIZE__ is
defined (which would happen at -O2 but not -O0). string2.h then
defines strdup(s) to __strdup(s) (line 1278 on my machine). string.h
says this can be inhibited by defining __NO_STRING_INLINES.

 - Hans