John Criswell
2015-May-06 14:28 UTC
[LLVMdev] (Possibly buggy?) doFinalization method behavior of FunctionPass
On 5/6/15 10:19 AM, Kuperstein, Michael M wrote:> > Hello Cristiano, > > I don’t think doFinalization() is really meant to be used this way. >My understanding is that doInitialization() and doFinalization() are designed specifically for modifying the LLVM IR (otherwise, why would a mutable reference to the Function be provided)? If that is not the case, then there is either a bug in the code or a bug in the documentation. That said, I agree with the suggestion of writing a ModulePass. Since the PassManager does not run FunctionPasses in parallel yet, there's little benefit to using them. I have often found the limitations on FunctionPasses to not be worth the hassle. Regards, John Criswell> Its purpose is to allow clean-up of internal data-structures used by > the pass itself, not to make additional changes to the module. > > One option would be to rewrite your pass as a ModulePass instead of a > FunctionPass, then iterating over the functions manually, and doing > the final clean-up once that’s done. > > Michael > > *From:*llvmdev-bounces at cs.uiuc.edu > [mailto:llvmdev-bounces at cs.uiuc.edu] *On Behalf Of *Cristianno Martins > *Sent:* Wednesday, May 06, 2015 03:20 > *To:* Lista LLVM-dev > *Subject:* [LLVMdev] (Possibly buggy?) doFinalization method behavior > of FunctionPass > > Hello there, > > I'm writing some LLVM passes, and just ran into an interesting > situation: now, I don't know if I misunderstood the way doFinalization > is supposed to work, but I hope someone could help =) > > One of the transformations I wrote needed to replace some instructions > within the code, so I needed to clean up the code after the process > was completed. The pass basically swapped some function calls (from > the standard C library) with my own implementation of those functions. > Changing the code in this way, though, creates some dead code (like > those dead prototypes that are not being used anymore). > > I, then, implemented the "clean up" strategy overriding > doFinalization. Unfortunately, any modifications done to the module in > this method appears to be ignored by LLVM. I even dumped the module > directly from within the method, and could see that the modifications > were applied to that reference of the module, but the .bc file opt > wrote into does not retain these changes. > > Now, bear with me here: I know that other passes like DCE could be > used to clean the bytecode, but some of the code I implemented in > doFinalization actually needed to run only once, and necessarily after > the pass has finished: this is where I check to see if there is some > extra situation I need to address, optimize some of the replaced > instructions, and verify if any of the functions that I want to remove > had their addresses taken by any instruction. > > Also, doFinalization has a bool return type, but it doesn't appear to > have any different behavior if I return either value =/ (I assumed the > general idea would be "return true if the module was modified in any > way", like runOnFunction, but I couldn't find anything to support that > anywhere). > > Thus, am I wrong about how to use doFinalization? If so, is there any > way to guarantee running some code only once and only when a pass > already finished its job? > > Thanks in advance, > > Oh, and before I forget, this is the version of the opt I'm running: > > LLVM (http://llvm.org/): > > LLVM version 3.7.0svn > > DEBUG build with assertions. > > Built May 4 2015 (00:18:21). > > Default target: x86_64-apple-darwin14.3.0 > > Host CPU: sandybridge > > > -- > Cristianno Martins > PhD Student of Computer Science > University of Campinas > cmartins at ic.unicamp.br <mailto:cmartins at ic.unicamp.br> > > --------------------------------------------------------------------- > Intel Israel (74) Limited > > This e-mail and any attachments may contain confidential material for > the sole use of the intended recipient(s). Any review or distribution > by others is strictly prohibited. If you are not the intended > recipient, please contact the sender and delete all copies. > > > > _______________________________________________ > LLVM Developers mailing list > LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev-- John Criswell Assistant Professor Department of Computer Science, University of Rochester http://www.cs.rochester.edu/u/criswell -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20150506/cbd959cc/attachment.html>
Kuperstein, Michael M
2015-May-06 15:15 UTC
[LLVMdev] (Possibly buggy?) doFinalization method behavior of FunctionPass
I've always thought that the only guarantee is that doFinalization(Module &M) runs after runOnFunction() was executed for all functions in M, and there's no guarantee it runs *immediately* after. That is, a PM may run a bunch of function passes over each function, and only then call doFinazliation() for each pass. That means that, even though you get a mutable reference to the module, the module you'll see is quite different from what you may expect. People more familiar with the pass managers - please correct me if I'm wrong. Michael From: John Criswell [mailto:jtcriswel at gmail.com] Sent: Wednesday, May 06, 2015 17:29 To: Kuperstein, Michael M; Cristianno Martins; Lista LLVM-dev Subject: Re: [LLVMdev] (Possibly buggy?) doFinalization method behavior of FunctionPass On 5/6/15 10:19 AM, Kuperstein, Michael M wrote: Hello Cristiano, I don't think doFinalization() is really meant to be used this way. My understanding is that doInitialization() and doFinalization() are designed specifically for modifying the LLVM IR (otherwise, why would a mutable reference to the Function be provided)? If that is not the case, then there is either a bug in the code or a bug in the documentation. That said, I agree with the suggestion of writing a ModulePass. Since the PassManager does not run FunctionPasses in parallel yet, there's little benefit to using them. I have often found the limitations on FunctionPasses to not be worth the hassle. Regards, John Criswell Its purpose is to allow clean-up of internal data-structures used by the pass itself, not to make additional changes to the module. One option would be to rewrite your pass as a ModulePass instead of a FunctionPass, then iterating over the functions manually, and doing the final clean-up once that's done. Michael From: llvmdev-bounces at cs.uiuc.edu<mailto:llvmdev-bounces at cs.uiuc.edu> [mailto:llvmdev-bounces at cs.uiuc.edu] On Behalf Of Cristianno Martins Sent: Wednesday, May 06, 2015 03:20 To: Lista LLVM-dev Subject: [LLVMdev] (Possibly buggy?) doFinalization method behavior of FunctionPass Hello there, I'm writing some LLVM passes, and just ran into an interesting situation: now, I don't know if I misunderstood the way doFinalization is supposed to work, but I hope someone could help =) One of the transformations I wrote needed to replace some instructions within the code, so I needed to clean up the code after the process was completed. The pass basically swapped some function calls (from the standard C library) with my own implementation of those functions. Changing the code in this way, though, creates some dead code (like those dead prototypes that are not being used anymore). I, then, implemented the "clean up" strategy overriding doFinalization. Unfortunately, any modifications done to the module in this method appears to be ignored by LLVM. I even dumped the module directly from within the method, and could see that the modifications were applied to that reference of the module, but the .bc file opt wrote into does not retain these changes. Now, bear with me here: I know that other passes like DCE could be used to clean the bytecode, but some of the code I implemented in doFinalization actually needed to run only once, and necessarily after the pass has finished: this is where I check to see if there is some extra situation I need to address, optimize some of the replaced instructions, and verify if any of the functions that I want to remove had their addresses taken by any instruction. Also, doFinalization has a bool return type, but it doesn't appear to have any different behavior if I return either value =/ (I assumed the general idea would be "return true if the module was modified in any way", like runOnFunction, but I couldn't find anything to support that anywhere). Thus, am I wrong about how to use doFinalization? If so, is there any way to guarantee running some code only once and only when a pass already finished its job? Thanks in advance, Oh, and before I forget, this is the version of the opt I'm running: LLVM (http://llvm.org/): LLVM version 3.7.0svn DEBUG build with assertions. Built May 4 2015 (00:18:21). Default target: x86_64-apple-darwin14.3.0 Host CPU: sandybridge -- Cristianno Martins PhD Student of Computer Science University of Campinas cmartins at ic.unicamp.br<mailto:cmartins at ic.unicamp.br> --------------------------------------------------------------------- Intel Israel (74) Limited This e-mail and any attachments may contain confidential material for the sole use of the intended recipient(s). Any review or distribution by others is strictly prohibited. If you are not the intended recipient, please contact the sender and delete all copies. _______________________________________________ LLVM Developers mailing list LLVMdev at cs.uiuc.edu<mailto:LLVMdev at cs.uiuc.edu> http://llvm.cs.uiuc.edu http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev -- John Criswell Assistant Professor Department of Computer Science, University of Rochester http://www.cs.rochester.edu/u/criswell --------------------------------------------------------------------- Intel Israel (74) Limited This e-mail and any attachments may contain confidential material for the sole use of the intended recipient(s). Any review or distribution by others is strictly prohibited. If you are not the intended recipient, please contact the sender and delete all copies. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20150506/1891a8da/attachment.html>
John Criswell
2015-May-06 16:01 UTC
[LLVMdev] (Possibly buggy?) doFinalization method behavior of FunctionPass
On 5/6/15 11:15 AM, Kuperstein, Michael M wrote:> > I’ve always thought that the only guarantee is that > doFinalization(Module &M) runs after runOnFunction() was executed for > all functions in M, and there’s no guarantee it runs *immediately* after. > > That is, a PM may run a bunch of function passes over each function, > and only then call doFinazliation() for each pass. That means that, > even though you get a mutable reference to the module, the module > you’ll see is quite different from what you may expect. >Correct. You're guaranteed that doFinalization() is run after your pass has been executed over all the functions. There's no guarantees about what other passes are going to do either before or after doFinalization() is called. Therefore, it's fine for doFinalization() to modify the Module. You just have to be aware that other passes may change the Module later. That's why I asked whether there are any other passes executed after Cristianno's pass: they can (theoretically) add the function declarations back into the Module. Regards, John Criswell> People more familiar with the pass managers – please correct me if I’m > wrong. > > Michael > > *From:*John Criswell [mailto:jtcriswel at gmail.com] > *Sent:* Wednesday, May 06, 2015 17:29 > *To:* Kuperstein, Michael M; Cristianno Martins; Lista LLVM-dev > *Subject:* Re: [LLVMdev] (Possibly buggy?) doFinalization method > behavior of FunctionPass > > On 5/6/15 10:19 AM, Kuperstein, Michael M wrote: > > Hello Cristiano, > > I don’t think doFinalization() is really meant to be used this way. > > > My understanding is that doInitialization() and doFinalization() are > designed specifically for modifying the LLVM IR (otherwise, why would > a mutable reference to the Function be provided)? > > If that is not the case, then there is either a bug in the code or a > bug in the documentation. > > That said, I agree with the suggestion of writing a ModulePass. Since > the PassManager does not run FunctionPasses in parallel yet, there's > little benefit to using them. I have often found the limitations on > FunctionPasses to not be worth the hassle. > > Regards, > > John Criswell > > > Its purpose is to allow clean-up of internal data-structures used by > the pass itself, not to make additional changes to the module. > > One option would be to rewrite your pass as a ModulePass instead of a > FunctionPass, then iterating over the functions manually, and doing > the final clean-up once that’s done. > > Michael > > *From:* llvmdev-bounces at cs.uiuc.edu > <mailto:llvmdev-bounces at cs.uiuc.edu> > [mailto:llvmdev-bounces at cs.uiuc.edu] *On Behalf Of *Cristianno Martins > *Sent:* Wednesday, May 06, 2015 03:20 > *To:* Lista LLVM-dev > *Subject:* [LLVMdev] (Possibly buggy?) doFinalization method behavior > of FunctionPass > > Hello there, > > I'm writing some LLVM passes, and just ran into an interesting > situation: now, I don't know if I misunderstood the way doFinalization > is supposed to work, but I hope someone could help =) > > One of the transformations I wrote needed to replace some instructions > within the code, so I needed to clean up the code after the process > was completed. The pass basically swapped some function calls (from > the standard C library) with my own implementation of those functions. > Changing the code in this way, though, creates some dead code (like > those dead prototypes that are not being used anymore). > > I, then, implemented the "clean up" strategy overriding > doFinalization. Unfortunately, any modifications done to the module in > this method appears to be ignored by LLVM. I even dumped the module > directly from within the method, and could see that the modifications > were applied to that reference of the module, but the .bc file opt > wrote into does not retain these changes. > > Now, bear with me here: I know that other passes like DCE could be > used to clean the bytecode, but some of the code I implemented in > doFinalization actually needed to run only once, and necessarily after > the pass has finished: this is where I check to see if there is some > extra situation I need to address, optimize some of the replaced > instructions, and verify if any of the functions that I want to remove > had their addresses taken by any instruction. > > Also, doFinalization has a bool return type, but it doesn't appear to > have any different behavior if I return either value =/ (I assumed the > general idea would be "return true if the module was modified in any > way", like runOnFunction, but I couldn't find anything to support that > anywhere). > > Thus, am I wrong about how to use doFinalization? If so, is there any > way to guarantee running some code only once and only when a pass > already finished its job? > > Thanks in advance, > > Oh, and before I forget, this is the version of the opt I'm running: > > LLVM (http://llvm.org/): > > LLVM version 3.7.0svn > > DEBUG build with assertions. > > Built May 4 2015 (00:18:21). > > Default target: x86_64-apple-darwin14.3.0 > > Host CPU: sandybridge > > > -- > Cristianno Martins > PhD Student of Computer Science > University of Campinas > cmartins at ic.unicamp.br <mailto:cmartins at ic.unicamp.br> > > --------------------------------------------------------------------- > Intel Israel (74) Limited > > This e-mail and any attachments may contain confidential material for > the sole use of the intended recipient(s). Any review or distribution > by others is strictly prohibited. If you are not the intended > recipient, please contact the sender and delete all copies. > > > > > _______________________________________________ > LLVM Developers mailing list > LLVMdev at cs.uiuc.edu <mailto:LLVMdev at cs.uiuc.edu> http://llvm.cs.uiuc.edu > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev > > > > > -- > John Criswell > Assistant Professor > Department of Computer Science, University of Rochester > http://www.cs.rochester.edu/u/criswell > > --------------------------------------------------------------------- > Intel Israel (74) Limited > > This e-mail and any attachments may contain confidential material for > the sole use of the intended recipient(s). Any review or distribution > by others is strictly prohibited. If you are not the intended > recipient, please contact the sender and delete all copies. >-- John Criswell Assistant Professor Department of Computer Science, University of Rochester http://www.cs.rochester.edu/u/criswell -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20150506/07829056/attachment.html>
Cristianno Martins
2015-May-06 16:11 UTC
[LLVMdev] (Possibly buggy?) doFinalization method behavior of FunctionPass
Hello again, First of all, thanks for all the answers =) they really helped a lot =D *Have you verified that some other pass is not adding the function declarations back in after your pass is executed (e.g., by using the -debug-pass=Executions argument to see what passes run after your pass)?* I considered that for a moment, but I realized that wouldn't be possible for two reasons: I specifically ran my pass with opt level zero; and one of the tasks I was doing was removing unused prototypes from the Module -- so, why would any other doFinalization pass reintroduce those prototypes if those functions were not being invoked anywhere? (PS: since this clean-up happened inside my doFinalization, I'm assuming only other doFinalization would be able to change the module after this point) *Also, does your doFinalization() method make other changes that are persistent?* The main reason why I chose to use doFinalization was to check if any of the functions I'm replacing still had any uses: since my pass replaced every function call with my respective function calls, if any uses could still be listed, that meant that some instruction must be taking the address of that function, and I should treat those instructions at this point. At the end, since I was already checking for uses, I ended up removing the extra prototypes at this point, if they were still there. I don’t think doFinalization() is really meant to be used this way. Its purpose is to allow clean-up of internal data-structures used by the pass itself, not to make additional changes to the module. Then, I have a question: why should doFinalization need a Module& as argument? I mean, since I shouldn't be able to modify it, and all data structures I created to work my pass are known and (mostly) directly accessible from within doFinalization, its argument would never be useful, right? One option would be to rewrite your pass as a ModulePass instead of a FunctionPass, then iterating over the functions manually, and doing the final clean-up once that’s done. *That said, I agree with the suggestion of writing a ModulePass. Since the PassManager does not run FunctionPasses in parallel yet, there's little benefit to using them. I have often found the limitations on FunctionPasses to not be worth the hassle.* Well, I actually wouldn't mind using a ModulePass to begin with, but unfortunately I had to rewrite my pass as a FunctionPass because part of the job it does involve accessing the DominatorTree -- and, unfortunately, I couldn't find a way to access it from inside a ModulePass. Even when I try to force a dependence between my module pass and DominatorTree, I can't get it to work because (if I'm not mistaken) module passes are hard-coded to run before function passes =/ *My understanding is that doInitialization() and doFinalization() are designed specifically for modifying the LLVM IR (otherwise, why would a mutable reference to the Function be provided)?* *If that is not the case, then there is either a bug in the code or a bug in the documentation.* Exactly like I thought =) I’ve always thought that the only guarantee is that doFinalization(Module &M) runs after runOnFunction() was executed for all functions in M, and there’s no guarantee it runs *immediately* after. That is, a PM may run a bunch of function passes over each function, and only then call doFinazliation() for each pass. That means that, even though you get a mutable reference to the module, the module you’ll see is quite different from what you may expect. People more familiar with the pass managers – please correct me if I’m wrong. I don't really mind at all if other passes run or even had their doFinalization passes running in any order in relation to mine: the point here is doFinalization is running (I know that because module.dump() is being called from inside that function, and I can see the module containing the modifications I do during the execution of that method), but the final bc file (written by opt) does have the exactly same code that I get if I dumped module at the beginning of my doFinalization (and they have differences between them btw =)). -- Cristianno Martins PhD Student of Computer Science University of Campinas cmartins at ic.unicamp.br <cristiannomartins at hotmail.com> -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20150506/2cb31db5/attachment.html>
Owen Anderson
2015-May-06 16:45 UTC
[LLVMdev] (Possibly buggy?) doFinalization method behavior of FunctionPass
> On May 6, 2015, at 7:28 AM, John Criswell <jtcriswel at gmail.com> wrote: > > My understanding is that doInitialization() and doFinalization() are designed specifically for modifying the LLVM IR (otherwise, why would a mutable reference to the Function be provided)?As the person whose use case motivated added them, we definitely didn’t intend them to be used for modifying IR. —Owen -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20150506/7fb97418/attachment.html>
John Criswell
2015-May-06 16:55 UTC
[LLVMdev] (Possibly buggy?) doFinalization method behavior of FunctionPass
Dear Owen, First, to be sure we're on the same page, are we talking about doFinalization() in a FunctionPass or the doFinalization() method of another type of pass? I've been assuming that we're talking about FunctionPasses. Second, according to the documentation, FunctionPass::doInitialization() is allowed to modify the IR. The documentation on doFinalization() does not say anything either way on the matter. It sounds like there's a bug in the documentation. Would you like me to file a bug report? Regards, John Criswell On 5/6/15 12:45 PM, Owen Anderson wrote:> >> On May 6, 2015, at 7:28 AM, John Criswell <jtcriswel at gmail.com >> <mailto:jtcriswel at gmail.com>> wrote: >> >> My understanding is that doInitialization() and doFinalization() are >> designed specifically for modifying the LLVM IR (otherwise, why would >> a mutable reference to the Function be provided)? > > As the person whose use case motivated added them, we definitely > didn’t intend them to be used for modifying IR. > > —Owen-- John Criswell Assistant Professor Department of Computer Science, University of Rochester http://www.cs.rochester.edu/u/criswell -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20150506/5e593678/attachment.html>