Well, you are an mclinker contributor and Google uses mclinker and now it's broken as the result of your change. I still don't see any justification to making a change in a public interface that is used by other non LLVM projects to fix some issue with clang warnings. People should be able to derive from those classes. I can't understand your reasoning as to why these classes must be final. I was kind of surprised that there are no mclinker build bots that would have picked this up right away. On 03/19/2015 09:08 AM, David Blaikie wrote:> > > On Thu, Mar 19, 2015 at 9:05 AM, Reed Kotler <reed.kotler at imgtec.com > <mailto:reed.kotler at imgtec.com>> wrote: > > On 03/19/2015 08:55 AM, David Blaikie wrote: >> >> >> On Thu, Mar 19, 2015 at 4:30 AM, Reed Kotler >> <Reed.Kotler at imgtec.com <mailto:Reed.Kotler at imgtec.com>> wrote: >> >> One could argue that mclinker is doing something good or not >> by how it's using this class >> but I don't see the need for parser<bool> to be final. That >> is a subjective opinion that mclinker needs to >> be changed. >> >> I think that "final" was added to some of these command line >> classes to avoid some kind of clang warning. >> >> That seems wrong to me that the tools are dictating something >> in an API. >> >> >> Well the warning's a pretty good one - and dictates a way to >> design an API safely to avoid the possibility of a bad delete. >> >> It's not uncommon to have a polymorphic hierarchy that doesn't >> require polymorphic ownership. To ensure that polymorphic >> ownership doesn't sneak in, we have a warning to ensure the class >> either has an interface compatible with polymorphic ownership >> (has a virtual dtor) or disallows polymorphic ownership (has a >> protected dtor in any non-final base). >> >> There is a narrower warning that only diagnoses this at the use >> of polymorphic destruction (-Wdelete-non-virtual-dtor) but we've >> not needed to fallback to that in LLVM so far & I'd mildly rather >> avoid doing so. The protected-final-or-virtual pattern seems >> fairly elegant/self-documenting to me. >> >> There may be other valid reasons to create derived classes. >> >> I think we should remove the "final" attribute on those >> classes and fix the clang warning issue in some >> better way than changing the API. >> >> If mclinker had been part of the llvm project tools tree that >> would not have been allowed even. >> >> >> Or we might've decided that the use in mclinker was bad & should >> be fixed - I haven't really looked at it to consider the details >> of its use, to be honest. > There are lots of valid reasons to want to be able to derive > classes; that's why C++ lets you do that. :) > > I don't think that LLVM judging MCLinker coding is relevant here. > > > It seems like it is to me - when refactoring code we look at the use > cases and judge what the right way to handle those use cases is. One > of those ways is to fix/change/remove the use-cases that seem > problematic/unnecessary/incorrect. > > Lots of projects use LLVM now and changing the API in this way > does not have justification other than to deal with some clang > warning issues that can be solved in other ways. > > > I think the practices that the clang warning enforces/encourages are > good ones, otherwise I would've fixed/changed/disabled the warning. > We've used these practices/this warning for a while now & it seems to > suit LLVM's use cases pretty well so far. > > I don't see any justification for deciding once and for all that > there are no valid reasons for deriving from these classes > and to use a c++ feature to enforce that. > > As I said earlier, had mclinker been in the tools subdirectory of > LLVM then the change the CommandLine.h would not have even been > allowed. > > > > >> >> ________________________________________ >> From: Simon Atanasyan [simon at atanasyan.com >> <mailto:simon at atanasyan.com>] >> Sent: Wednesday, March 18, 2015 9:35 PM >> To: Reed Kotler >> Cc: David Blaikie; Simon Atanasyan; Rich Fuhler; >> llvmdev at cs.uiuc.edu <mailto:llvmdev at cs.uiuc.edu> >> Subject: Re: [LLVMdev] Final added to parser<bool> >> >> Hi Reed, >> >> The FalseParser has a rather strange design. It's purpose to >> parse >> options like -no-to-do-something and always return false even >> if a >> user provides -no-to-do-something=no. That should be fixed on the >> MCLinker side. >> >> On Thu, Mar 19, 2015 at 5:14 AM, reed kotler >> <rkotler at mips.com <mailto:rkotler at mips.com>> wrote: >> > >> //===----------------------------------------------------------------------===// >> > // FalseParser >> > >> //===----------------------------------------------------------------------===// >> > class FalseParser : public parser<bool> { >> > public: >> > explicit FalseParser(Option &O) : parser<bool>(O) { } >> > >> > // parse - Return true on error. >> > bool parse(cl::Option& O, StringRef ArgName, StringRef >> Arg, bool& Val) { >> > if (cl::parser<bool>::parse(O, ArgName, Arg, Val)) >> > return false; >> > Val = false; >> > return false; >> > } >> > }; >> > >> > I don't know the history of this. I'm just starting to do >> some mclinker work >> > to add the new mips r6 relocations to it. >> > >> > >> > On 03/18/2015 07:00 PM, David Blaikie wrote: >> > >> > >> > >> > On Wed, Mar 18, 2015 at 6:48 PM, reed kotler >> <rkotler at mips.com <mailto:rkotler at mips.com>> wrote: >> >> >> >> Hi David, >> >> >> >> Is there a reason that we need to have "final" for >> parser<bool> ??? >> > >> > >> > Clang has a (reasonable) warning for types with virtual >> functions and a >> > non-virtual dtor. This warning is suppressed if the dtor is >> protected or the >> > class is final (since in the first case it's clear that the >> user intends not >> > to destroy objects via base pointers, only derived ones - >> and in the second >> > case there's no risk of derived classes, so public access >> to the dtor is >> > safe even without virtual dispatch. >> > >> > Since the parser hierarchy never needed polymorphic >> destruction (all >> > instances are concrete instances of derived classes owned >> and destroyed >> > directly, not via base pointers) this seemed like a fine >> way to structure >> > the API. >> >> -- >> Simon Atanasyan >> >> > >-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20150319/e04cc198/attachment.html>
On Thu, Mar 19, 2015 at 9:18 AM, Reed Kotler <reed.kotler at imgtec.com> wrote:> Well, you are an mclinker contributor >Me personally? Not that I know of.> and Google uses mclinker >So I've been told, though I hadn't even heard of mclinker until this email thread.> and now it's broken as the result of your change. >This is a pretty standard state of affairs for LLVM-using projects, LLVM's APIs change continuously.> I still don't see any justification to making a change in a public > interface that is used by other non LLVM projects > to fix some issue with clang warnings. People should be able to derive > from those classes. I can't understand > your reasoning as to why these classes must be final. >Because if they're not, it's easy to write bugs with them - especially in non-tree projects, strangely enough. (if you derive from this type, then happen to own those derived objects polymorphically, you'll invoke undefined behavior - by making the type 'final' it removes the ability to write such bugs).> I was kind of surprised that there are no mclinker build bots that would > have picked this up right away. > > > On 03/19/2015 09:08 AM, David Blaikie wrote: > > > > On Thu, Mar 19, 2015 at 9:05 AM, Reed Kotler <reed.kotler at imgtec.com> > wrote: > >> On 03/19/2015 08:55 AM, David Blaikie wrote: >> >> >> >> On Thu, Mar 19, 2015 at 4:30 AM, Reed Kotler <Reed.Kotler at imgtec.com> >> wrote: >> >>> One could argue that mclinker is doing something good or not by how it's >>> using this class >>> but I don't see the need for parser<bool> to be final. That is a >>> subjective opinion that mclinker needs to >>> be changed. >>> >>> I think that "final" was added to some of these command line classes to >>> avoid some kind of clang warning. >>> >>> That seems wrong to me that the tools are dictating something in an API. >>> >> >> Well the warning's a pretty good one - and dictates a way to design an >> API safely to avoid the possibility of a bad delete. >> >> It's not uncommon to have a polymorphic hierarchy that doesn't require >> polymorphic ownership. To ensure that polymorphic ownership doesn't sneak >> in, we have a warning to ensure the class either has an interface >> compatible with polymorphic ownership (has a virtual dtor) or disallows >> polymorphic ownership (has a protected dtor in any non-final base). >> >> There is a narrower warning that only diagnoses this at the use of >> polymorphic destruction (-Wdelete-non-virtual-dtor) but we've not needed to >> fallback to that in LLVM so far & I'd mildly rather avoid doing so. The >> protected-final-or-virtual pattern seems fairly elegant/self-documenting to >> me. >> >> >>> There may be other valid reasons to create derived classes. >>> >>> I think we should remove the "final" attribute on those classes and fix >>> the clang warning issue in some >>> better way than changing the API. >>> >>> If mclinker had been part of the llvm project tools tree that would not >>> have been allowed even. >>> >> >> Or we might've decided that the use in mclinker was bad & should be fixed >> - I haven't really looked at it to consider the details of its use, to be >> honest. >> >> >> There are lots of valid reasons to want to be able to derive classes; >> that's why C++ lets you do that. :) >> >> I don't think that LLVM judging MCLinker coding is relevant here. >> > > It seems like it is to me - when refactoring code we look at the use cases > and judge what the right way to handle those use cases is. One of those > ways is to fix/change/remove the use-cases that seem > problematic/unnecessary/incorrect. > > >> Lots of projects use LLVM now and changing the API in this way >> does not have justification other than to deal with some clang warning >> issues that can be solved in other ways. >> > > I think the practices that the clang warning enforces/encourages are good > ones, otherwise I would've fixed/changed/disabled the warning. We've used > these practices/this warning for a while now & it seems to suit LLVM's use > cases pretty well so far. > > >> I don't see any justification for deciding once and for all that there >> are no valid reasons for deriving from these classes >> and to use a c++ feature to enforce that. >> >> As I said earlier, had mclinker been in the tools subdirectory of LLVM >> then the change the CommandLine.h would not have even been allowed. >> >> >> >> >> >>> ________________________________________ >>> From: Simon Atanasyan [simon at atanasyan.com] >>> Sent: Wednesday, March 18, 2015 9:35 PM >>> To: Reed Kotler >>> Cc: David Blaikie; Simon Atanasyan; Rich Fuhler; llvmdev at cs.uiuc.edu >>> Subject: Re: [LLVMdev] Final added to parser<bool> >>> >>> Hi Reed, >>> >>> The FalseParser has a rather strange design. It's purpose to parse >>> options like -no-to-do-something and always return false even if a >>> user provides -no-to-do-something=no. That should be fixed on the >>> MCLinker side. >>> >>> On Thu, Mar 19, 2015 at 5:14 AM, reed kotler <rkotler at mips.com> wrote: >>> > >>> //===----------------------------------------------------------------------===// >>> > // FalseParser >>> > >>> //===----------------------------------------------------------------------===// >>> > class FalseParser : public parser<bool> { >>> > public: >>> > explicit FalseParser(Option &O) : parser<bool>(O) { } >>> > >>> > // parse - Return true on error. >>> > bool parse(cl::Option& O, StringRef ArgName, StringRef Arg, bool& >>> Val) { >>> > if (cl::parser<bool>::parse(O, ArgName, Arg, Val)) >>> > return false; >>> > Val = false; >>> > return false; >>> > } >>> > }; >>> > >>> > I don't know the history of this. I'm just starting to do some >>> mclinker work >>> > to add the new mips r6 relocations to it. >>> > >>> > >>> > On 03/18/2015 07:00 PM, David Blaikie wrote: >>> > >>> > >>> > >>> > On Wed, Mar 18, 2015 at 6:48 PM, reed kotler <rkotler at mips.com> wrote: >>> >> >>> >> Hi David, >>> >> >>> >> Is there a reason that we need to have "final" for parser<bool> ??? >>> > >>> > >>> > Clang has a (reasonable) warning for types with virtual functions and a >>> > non-virtual dtor. This warning is suppressed if the dtor is protected >>> or the >>> > class is final (since in the first case it's clear that the user >>> intends not >>> > to destroy objects via base pointers, only derived ones - and in the >>> second >>> > case there's no risk of derived classes, so public access to the dtor >>> is >>> > safe even without virtual dispatch. >>> > >>> > Since the parser hierarchy never needed polymorphic destruction (all >>> > instances are concrete instances of derived classes owned and destroyed >>> > directly, not via base pointers) this seemed like a fine way to >>> structure >>> > the API. >>> >>> -- >>> Simon Atanasyan >>> >> >> >> > >-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20150319/2a92aac1/attachment.html>
On Thu, Mar 19, 2015 at 7:18 PM, Reed Kotler <reed.kotler at imgtec.com> wrote:> I still don't see any justification to making a change in a public interface > that is used by other non LLVM projects > to fix some issue with clang warnings. People should be able to derive from > those classes. I can't understand > your reasoning as to why these classes must be final.>From my point of view this class is a good candidate to be final. Icannot realize a real test case when somebody needs to extend parsing of boolean command line flags. If MCLinker had been part of the LLVM project the FalseParser design would not have passed review.> I was kind of surprised that there are no mclinker build bots that would > have picked this up right away.MCLinker does not use LLVM ToT. It migrates to the fresh version of LLVM from time to time. Simon Atanasyan
On 03/19/2015 09:24 AM, David Blaikie wrote:> > > On Thu, Mar 19, 2015 at 9:18 AM, Reed Kotler <reed.kotler at imgtec.com > <mailto:reed.kotler at imgtec.com>> wrote: > > Well, you are an mclinker contributor > > > Me personally? Not that I know of.Sorry. I thought i had seen your name in an mclinker commit.> > and Google uses mclinker > > > So I've been told, though I hadn't even heard of mclinker until this > email thread.It's another linker (we don't have enough of them :) ) . It's used to run on mobile devices and has been designed with that criteria in mind. (At least that is my understanding).> and now it's broken as the result of your change. > > > This is a pretty standard state of affairs for LLVM-using projects, > LLVM's APIs change continuously.Probably then this is a configuration issue I need to take up with mclinker folks. Their build instructions have you just download tip of tree from svn and that clearly is not guaranteed to work. Probably their wiki should list the version from LLVM to download.> I still don't see any justification to making a change in a public > interface that is used by other non LLVM projects > to fix some issue with clang warnings. People should be able to > derive from those classes. I can't understand > your reasoning as to why these classes must be final. > > > Because if they're not, it's easy to write bugs with them - especially > in non-tree projects, strangely enough. (if you derive from this type, > then happen to own those derived objects polymorphically, you'll > invoke undefined behavior - by making the type 'final' it removes the > ability to write such bugs).Isn't that a problem with the design of this class? (or these classes)?> I was kind of surprised that there are no mclinker build bots that > would have picked this up right away. > > > On 03/19/2015 09:08 AM, David Blaikie wrote: >> >> >> On Thu, Mar 19, 2015 at 9:05 AM, Reed Kotler >> <reed.kotler at imgtec.com <mailto:reed.kotler at imgtec.com>> wrote: >> >> On 03/19/2015 08:55 AM, David Blaikie wrote: >>> >>> >>> On Thu, Mar 19, 2015 at 4:30 AM, Reed Kotler >>> <Reed.Kotler at imgtec.com <mailto:Reed.Kotler at imgtec.com>> wrote: >>> >>> One could argue that mclinker is doing something good or >>> not by how it's using this class >>> but I don't see the need for parser<bool> to be final. >>> That is a subjective opinion that mclinker needs to >>> be changed. >>> >>> I think that "final" was added to some of these command >>> line classes to avoid some kind of clang warning. >>> >>> That seems wrong to me that the tools are dictating >>> something in an API. >>> >>> >>> Well the warning's a pretty good one - and dictates a way to >>> design an API safely to avoid the possibility of a bad delete. >>> >>> It's not uncommon to have a polymorphic hierarchy that >>> doesn't require polymorphic ownership. To ensure that >>> polymorphic ownership doesn't sneak in, we have a warning to >>> ensure the class either has an interface compatible with >>> polymorphic ownership (has a virtual dtor) or disallows >>> polymorphic ownership (has a protected dtor in any non-final >>> base). >>> >>> There is a narrower warning that only diagnoses this at the >>> use of polymorphic destruction (-Wdelete-non-virtual-dtor) >>> but we've not needed to fallback to that in LLVM so far & >>> I'd mildly rather avoid doing so. The >>> protected-final-or-virtual pattern seems fairly >>> elegant/self-documenting to me. >>> >>> There may be other valid reasons to create derived classes. >>> >>> I think we should remove the "final" attribute on those >>> classes and fix the clang warning issue in some >>> better way than changing the API. >>> >>> If mclinker had been part of the llvm project tools tree >>> that would not have been allowed even. >>> >>> >>> Or we might've decided that the use in mclinker was bad & >>> should be fixed - I haven't really looked at it to consider >>> the details of its use, to be honest. >> There are lots of valid reasons to want to be able to derive >> classes; that's why C++ lets you do that. :) >> >> I don't think that LLVM judging MCLinker coding is relevant >> here. >> >> >> It seems like it is to me - when refactoring code we look at the >> use cases and judge what the right way to handle those use cases >> is. One of those ways is to fix/change/remove the use-cases that >> seem problematic/unnecessary/incorrect. >> >> Lots of projects use LLVM now and changing the API in this way >> does not have justification other than to deal with some >> clang warning issues that can be solved in other ways. >> >> >> I think the practices that the clang warning enforces/encourages >> are good ones, otherwise I would've fixed/changed/disabled the >> warning. We've used these practices/this warning for a while now >> & it seems to suit LLVM's use cases pretty well so far. >> >> I don't see any justification for deciding once and for all >> that there are no valid reasons for deriving from these classes >> and to use a c++ feature to enforce that. >> >> As I said earlier, had mclinker been in the tools >> subdirectory of LLVM then the change the CommandLine.h would >> not have even been allowed. >> >> >> >> >>> >>> ________________________________________ >>> From: Simon Atanasyan [simon at atanasyan.com >>> <mailto:simon at atanasyan.com>] >>> Sent: Wednesday, March 18, 2015 9:35 PM >>> To: Reed Kotler >>> Cc: David Blaikie; Simon Atanasyan; Rich Fuhler; >>> llvmdev at cs.uiuc.edu <mailto:llvmdev at cs.uiuc.edu> >>> Subject: Re: [LLVMdev] Final added to parser<bool> >>> >>> Hi Reed, >>> >>> The FalseParser has a rather strange design. It's >>> purpose to parse >>> options like -no-to-do-something and always return false >>> even if a >>> user provides -no-to-do-something=no. That should be >>> fixed on the >>> MCLinker side. >>> >>> On Thu, Mar 19, 2015 at 5:14 AM, reed kotler >>> <rkotler at mips.com <mailto:rkotler at mips.com>> wrote: >>> > >>> //===----------------------------------------------------------------------===// >>> > // FalseParser >>> > >>> //===----------------------------------------------------------------------===// >>> > class FalseParser : public parser<bool> { >>> > public: >>> > explicit FalseParser(Option &O) : parser<bool>(O) { } >>> > >>> > // parse - Return true on error. >>> > bool parse(cl::Option& O, StringRef ArgName, >>> StringRef Arg, bool& Val) { >>> > if (cl::parser<bool>::parse(O, ArgName, Arg, Val)) >>> > return false; >>> > Val = false; >>> > return false; >>> > } >>> > }; >>> > >>> > I don't know the history of this. I'm just starting to >>> do some mclinker work >>> > to add the new mips r6 relocations to it. >>> > >>> > >>> > On 03/18/2015 07:00 PM, David Blaikie wrote: >>> > >>> > >>> > >>> > On Wed, Mar 18, 2015 at 6:48 PM, reed kotler >>> <rkotler at mips.com <mailto:rkotler at mips.com>> wrote: >>> >> >>> >> Hi David, >>> >> >>> >> Is there a reason that we need to have "final" for >>> parser<bool> ??? >>> > >>> > >>> > Clang has a (reasonable) warning for types with >>> virtual functions and a >>> > non-virtual dtor. This warning is suppressed if the >>> dtor is protected or the >>> > class is final (since in the first case it's clear >>> that the user intends not >>> > to destroy objects via base pointers, only derived >>> ones - and in the second >>> > case there's no risk of derived classes, so public >>> access to the dtor is >>> > safe even without virtual dispatch. >>> > >>> > Since the parser hierarchy never needed polymorphic >>> destruction (all >>> > instances are concrete instances of derived classes >>> owned and destroyed >>> > directly, not via base pointers) this seemed like a >>> fine way to structure >>> > the API. >>> >>> -- >>> Simon Atanasyan >>> >>> >> >> > >-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20150319/1bc60015/attachment.html>
On 03/19/2015 09:27 AM, Simon Atanasyan wrote:> On Thu, Mar 19, 2015 at 7:18 PM, Reed Kotler <reed.kotler at imgtec.com> wrote: >> I still don't see any justification to making a change in a public interface >> that is used by other non LLVM projects >> to fix some issue with clang warnings. People should be able to derive from >> those classes. I can't understand >> your reasoning as to why these classes must be final. > From my point of view this class is a good candidate to be final. I > cannot realize a real test case when somebody needs to extend parsing > of boolean command line flags. If MCLinker had been part of the LLVM > project the FalseParser design would not have passed review. >Isn't this a problem without how these classes were designed as opposed to a problem with someone wanting to derive from ?>> I was kind of surprised that there are no mclinker build bots that would >> have picked this up right away. > MCLinker does not use LLVM ToT. It migrates to the fresh version of > LLVM from time to time.Seems like we need to fix the mclinker wiki so that people know which version to use. The mclinker instructions just have one checking out from tip of tree.> Simon Atanasyan