[LLVMdev] Inter-procedural program flow analysis

[Scott Moore]

I think you're looking for an inter-procedural post dominator analysis. I
don't think there is one in LLVM already, but it should be relatively
straightforward.

This gives a sound approximation (i.e. no false positives) of something
sort-of equivalent to the halting problem: if the program terminates, then
block Y was executed.

Cheers,
Scott


On Tue, Oct 2, 2012 at 7:43 PM, Jim Grosbach <grosbach at apple.com> wrote:

> Isn't this effectively the halting problem? Consider the case where block
> Y is the exit block of main() and block X is the entry block of main().
>
> Jim
>
>
> On Oct 2, 2012, at 4:29 PM, Stephen Schiffli <sschiffli at gmail.com> wrote:
>
> Is there any inter-procedural analysis that could tell me if some
> BasicBlock Y is guaranteed to execute based on my knowledge that BasicBlock
> X will execute?  For example:
>
>
> extern int x;
>
> void foo() { }
>
> int main() {
>
>             if (x) {
>
>                         foo();
>
>             } else {
>
>                         foo();
>
> }
>
> }
>
>
> I want to be told that the entry block of foo is guaranteed to be executed
> since I know the entry block of main is guaranteed to be executed.
>  Basically that all paths from X to program termination go through Y at
> some point.  Please ignore the folding of identical branches and
> function in-lining, I want to use this type of analysis in the general case.
>
>
> Thanks,
>
> -Stephen
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