[LLVMdev] The problem of densemap and loop

[Hanbing Li]

Dear John, 

Thank you for your answer. 
The bad news is that I need to apply several optimizations between the store and read. So the CFG will be modified. 
Anyway, I will find another way out. 

Thank you very much! 

Sincerely, 

Hanbing 

----- Mail original -----

> De: "John Criswell" <jtcriswel at gmail.com>
> À: "Hanbing Li" <hanbing.li at inria.fr>, llvmdev at cs.uiuc.edu
> Envoyé: Vendredi 29 Août 2014 15:24:52
> Objet: Re: [LLVMdev] The problem of densemap and loop

> On 8/29/14, 8:52 AM, Hanbing Li wrote:

> > Hi,
> 

> > I tried to solve the problem by myself. And when I even got the densemap
> > with
> > 6 items, I still got 0 in another ModulePass by using the loopinfo derived
> > in the new ModulePass. So if this means that when I use a loop in LoopInfo
> > in a Function/ModulePass, I can't get the same loop object in another
> > ModulePass. In other words, the loop objects in two ModulePasses are always
> > different?
> 

> I think that the loop objects retrieved by two different ModulePasses would
> be different. The reason is that the PassManager tells the LoopInfo pass (a
> FunctionPass) to reinitialize itself every time it is run from a ModulePass.
> You therefore cannot call getAnalysis<LoopInfo>(F), grab a pointer to a Loop
> returned from the FunctionPass, and save it; the Loop object will be deleted
> (and its memory potentially reused) on the next call to getAnalysis.

> What you should do in your ModulePass is something like the following:

> for (every function F in the Module) {
> container box;
> for (every Loop L in the Function F) {
> Add L to box
> }

> for (every Loop L in box) {
> Do with loop whatever you are going to do with it
> }
> }

> If you really need to track all loops in all functions in a single data
> structure (and assuming that I'm correct that LoopInfo gets reinitialized),
> then I think there is something else you can do: instead of recording a
> pointer to the Loop object, record the basic block of the loop's header and
> the loop's nesting level. When you then need the Loop object, you run the
> LoopInfo pass on the function to which the basic block belongs and find the
> loop with the matching header basic block. As long as the CFG isn't modified
> in between the time you record the basic blocks and the time you look up the
> LoopInfo, this should work.

> Hope this helps,

> John Criswell
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20140829/615bdd03/attachment.html>