[LLVMdev] Processing functions in call graph SCC "order" with function-level analyses

[Daniel Berlin]

On Tue, May 19, 2015 at 8:38 PM, Félix Cloutier <felixcca at yahoo.ca> wrote:
> So I got very mixed results.
>
> With the CallGraphSCCPass, both `addRequired<DominatorTreeWrapperPass>` and
> `addRequired<MemoryDependenceAnalysis>` fail at runtime. The LLVM core has
> just two CallGraphSCCPasses and neither uses neither analyses, so it's hard
> to find a valid example.
>

Have you tried INITIALIZE_PASS_BEGIN and INITIALIZE_PASS_DEPENDENCY?


> I transformed the pass into a ModulePass, using scc_iterator as shown in
> CGPassManager to process functions in order, and the situation isn't a whole
> lot better.
>
> Interestingly, `addRequired<CallGraphWrapperPass>()` failed on me, even
> though at first glance, CGPassManager doesn't seem to be doing anything that
> I'm not doing. This is relatively easily bypassed by creating the CallGraph
> from runOnModule.
>
> `addRequired<MemoryDependenceAnalysis>()` fails with this error message:
>
> Pass 'My Pass' is not initialized.

You haven't used INTIIALIZE_PASS_*

> Verify if there is a pass dependency cycle.
> Required Passes:
> Dominator Tree Construction
> Assertion failed: (PI && "Expected required passes to be initialized"),
> function schedulePass, file LegacyPassManager.cpp, line 641.
>
>
> "Dominator Tree Construction" disappears from the error message (leaving an
> empty list of required passes) if I move its `addRequired` *after* MemDep's.
>
> `addRequired<DominatorTreeWrapperPass>()` worked instantly, so there's that,
> I suppose.
>
> This all looks like rather basic things to do with the pass architecture,
> and I can't seem to find documentation explaining which analyses can be used
> in which types of passes. As I can only find examples of MemDep in
> FunctionPasses, I'll probably switch over to that, but this is going to be
> frustrating when I'll need call graph SCC information. Anyone has a better
> idea?
>
> I should note that I'm not using the INITIALIZE_PASS macros because I have
> no idea how they mesh with RegisterPass. I'm seeing that the passes that use
> these have INITIALIZE_PASS_DEPENDENCY macros and it makes me a little
> nervous, but the resulting function for my pass is seemingly never called.
>
> Félix
>
> Le 2015-05-19 à 12:47:32, John Criswell <jtcriswel at gmail.com> a écrit :
>
> On 5/19/15 10:04 AM, Félix Cloutier wrote:
>
> Thanks John.
>
> Does this solve the problem of analysis availability though? If I still have
> to run the function analyses manually, I might as well keep rolling with the
> CallGraphSCCPass. (I probably should have mentioned that this is what I’m
> using right now.)
>
>
> I'm not sure what you mean by "manually."  If you use a ModulePass, you can
> use the getAnalysis<FunctionPassName>(F) method to get a reference to a
> function pass.  The ModulePass's getAnalysisUsage() method will need to use
> addRequired<FunctionPass>() to require each FunctionPass, but I think the
> PassManager will run the passes automatically as needed.
>
> Note that you cannot use the PassManager to ensure that certain optimization
> passes are run before your pass is run.  If you need to run an optimization
> pass before your pass (e.g., UnifyExitNodes), then you need to tell the
> PassManager to run it before your pass explicitly.
>
> Regards,
>
> John Criswell
>
>
> Félix
>
> Le 2015-05-19 à 10:12:32, John Criswell <jtcriswel at gmail.com> a écrit :
>
> On 5/18/15 10:45 PM, Félix Cloutier wrote:
>
> Hi all,
>
> I have one analysis pass that I want to perform on call graph SCCs. However,
> for each function in the SCC, I need function-level analyses, like the
> dominator tree and the memory dependency analysis.
>
> I’ve been told before that these were not available from a CallGraphSCCPass.
> What would be the best approach for me to access this information? Should I
> run the passes manually, or is there another, more pass-scheduler-friendly
> approach?
>
>
> I would write a ModulePass that simply iterates over the call graph.  LLVM
> provides a CallGraph analysis which one can use to find SCCs; DSA has an
> analysis called CallTargets which does "real" CallGraph analysis (which
> means that it tries to reason about function pointers, though I cannot
> guarantee that its reasoning will be as accurate as you want).
>
> If you use a ModulePass, can you analyze any part of the program you like,
> and you can use FunctionPasses.
>
> Regards,
>
> John Criswell
>
>
> Félix
>
>
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>
> --
> John Criswell
> Assistant Professor
> Department of Computer Science, University of Rochester
> http://www.cs.rochester.edu/u/criswell
>
>
>
>
> --
> John Criswell
> Assistant Professor
> Department of Computer Science, University of Rochester
> http://www.cs.rochester.edu/u/criswell
>
>
>
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