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

[Félix Cloutier]

So yes, for the record, it works with ModulePass.

Any idea why it didn't with CallGraphSCCPass?

Félix

> Le 2015-05-19 à 23:49:22, Daniel Berlin <dberlin at dberlin.org> a écrit :
> 
> 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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