llvm dev - Jan 2014 - [LLVMdev] "Function" file name

Folks, 


I am newbie to llvm! 


I am writing a simple pass that inherits from ModulePass. I override the
runOnModule method. In the method, i am attempting to print all the function in
the module and the source-file they appear in. I could print the name of the
function using the Module::iterator. I am, however, not able to figure-out the
way to identify the source-file for a given "Function". Any help in
this regards is appreciated.


Thanks and with best regards, 
Nizam 

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Hi Nizam,
> I am writing a simple pass that inherits from ModulePass. I override the
> runOnModule method. In the method, i am attempting to print all the
function
> in the module and the source-file they appear in. I could print the name of
> the function using the Module::iterator. I am, however, not able to
> figure-out the way to identify the source-file for a given
"Function".
That information is generally only present if the file was compiled
with debug info ("clang -g"), and even then I believe it's only
attached to the instructions in a function rather than the function
itself. Inlining can complicate things further, so you need to pick
the *right* instruction (some may come from a different file
entirely).

Some grubbing around the class hierarchy suggests this procedure:
1. Find a "ret" instruction in the function (actually, a function can
rarely exist with "unreachable" instead of "ret" so be
careful).
2. Call Instruction::getDebugLoc on it
3. Call DebugLoc::getAsMDNode to convert it into an MDNode
4. Create a DILocation from that MDNode and query it for your info.

There may be a simpler way, but hopefully that will do the job.

Cheers.

Tim.

This should work, but I think a more standard approach (though arguably slower)
is to use DebugInfoFinder (from DebugInfo.h).

So create a DebugInfoFinder, process the module with it, and then iterate over
all the subprograms to find the one matching your function. Roughly something
like:

DebugInfoFinder Finder;
Finder.processModule(F->getParent());
for (DebugInfoFinder::iterator Iter = Finder.subprogram_begin(),
    End = Finder.subprogram_end(); Iter != End; ++Iter) {
  const MDNode* node = *Iter;
  DISubprogram SP(node);
  if (SP.describes(F)) return SP.getFilename();
}

-----Original Message-----
From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu] On
Behalf Of Tim Northover
Sent: Thursday, January 30, 2014 10:07
To: nizam at cse.iitm.ac.in
Cc: LLVM Developers Mailing List
Subject: Re: [LLVMdev] "Function" file name

Hi Nizam,
> I am writing a simple pass that inherits from ModulePass. I override 
> the runOnModule method. In the method, i am attempting to print all 
> the function in the module and the source-file they appear in. I could 
> print the name of the function using the Module::iterator. I am, 
> however, not able to figure-out the way to identify the source-file for a
given "Function".
That information is generally only present if the file was compiled with debug
info ("clang -g"), and even then I believe it's only attached to
the instructions in a function rather than the function itself. Inlining can
complicate things further, so you need to pick the *right* instruction (some may
come from a different file entirely).

Some grubbing around the class hierarchy suggests this procedure:
1. Find a "ret" instruction in the function (actually, a function can
rarely exist with "unreachable" instead of "ret" so be
careful).
2. Call Instruction::getDebugLoc on it
3. Call DebugLoc::getAsMDNode to convert it into an MDNode 4. Create a
DILocation from that MDNode and query it for your info.

There may be a simpler way, but hopefully that will do the job.

Cheers.

Tim.
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