Would it be possible to keep get() unchanged, with a default behaviour, plus a warning? Otherwise everybody (assuming everybody gets type void*) will have to update their LLVM passes, and either maintain two versions of the passes or require their clients to use a certain LLVM version. Then passes could be "address-space-safe" or not. If the default parameter value for get() could be a unique ID for "not specified" instead of "the default address space", then one should even be able to continue to use get() isntead of sth like getQual(...). Torvald On Monday 17 December 2007, Christopher Lamb wrote:> On Dec 16, 2007, at 10:22 PM, Anton Korobeynikov wrote: > > Christopher, > > > >> The API for getting PointerType objects has just changed to make > >> Embedded C address space information explicit. The old semantics of > >> PointerType::get() now apply to PointerType::getUnqual(), which > >> returns a pointer in the generic address space. PointerType::get() > >> now > >> requires both a type and an address space. > > > > What is the reason of such change? > > Sorry for not providing that. Here's the conversation with Chris: > > On Dec 12, 2007, at 1:32 AM, Christopher Lamb wrote: > >> On Dec 11, 2007, at 4:12 PM, Chris Lattner wrote: > >>> Making the address space default to zero is convenient, but > >>> dangerous. This means that xforms that play with pointers need > >>> to be > >>> very careful to propagate this info in some cases. Do you think > >>> this > >>> is the best way to go? Do many clients of PointerType::get need to > >>> be aware of addr spaces? > >> > >> I'm going to add a new method for getting a pointer type > >> 'PointerType::getUnqual()' that only takes an element type, the > >> standard 'PointerType::get()' will take both an element type and > >> address space with no default values. This should at least make it > >> explicit in the code which clients do not pass in an address space. > >> There are currently many clients, so this should help make the work > >> incremental. > > > > Excellent idea, > > > > -Chris > > -- > Christopher Lamb
On Dec 17, 2007, at 1:22 AM, Torvald Riegel wrote:> Would it be possible to keep get() unchanged, with a default > behaviour, plus > a warning? Otherwise everybody (assuming everybody gets type void*) > will > have to update their LLVM passes, and either maintain two versions > of the > passes or require their clients to use a certain LLVM version.AFAIK API compatibility is not guaranteed across LLVM point releases, so I believe clients are tied to a specific version of LLVM in any case.> Then passes > could be "address-space-safe" or not. If the default parameter > value for > get() could be a unique ID for "not specified" instead of "the default > address space", then one should even be able to continue to use get() > isntead of sth like getQual(...).The reason for the change was to make it absolutely clear in the source where address space qualifiers are preserved/added or stripped from the pointer type. Allowing clients to use get() and then dynamically track "undefined" address spaces under the hood is counter to this goal.> On Monday 17 December 2007, Christopher Lamb wrote: >> On Dec 16, 2007, at 10:22 PM, Anton Korobeynikov wrote: >>> Christopher, >>> >>>> The API for getting PointerType objects has just changed to make >>>> Embedded C address space information explicit. The old semantics of >>>> PointerType::get() now apply to PointerType::getUnqual(), which >>>> returns a pointer in the generic address space. PointerType::get() >>>> now >>>> requires both a type and an address space. >>> >>> What is the reason of such change? >> >> Sorry for not providing that. Here's the conversation with Chris: >>> On Dec 12, 2007, at 1:32 AM, Christopher Lamb wrote: >>>> On Dec 11, 2007, at 4:12 PM, Chris Lattner wrote: >>>>> Making the address space default to zero is convenient, but >>>>> dangerous. This means that xforms that play with pointers need >>>>> to be >>>>> very careful to propagate this info in some cases. Do you think >>>>> this >>>>> is the best way to go? Do many clients of PointerType::get >>>>> need to >>>>> be aware of addr spaces? >>>> >>>> I'm going to add a new method for getting a pointer type >>>> 'PointerType::getUnqual()' that only takes an element type, the >>>> standard 'PointerType::get()' will take both an element type and >>>> address space with no default values. This should at least make it >>>> explicit in the code which clients do not pass in an address space. >>>> There are currently many clients, so this should help make the work >>>> incremental. >>> >>> Excellent idea, >>> >>> -Chris >> >> -- >> Christopher Lamb >-- Christopher Lamb -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20071217/8105dc8a/attachment.html>
On Monday 17 December 2007, Christopher Lamb wrote:> On Dec 17, 2007, at 1:22 AM, Torvald Riegel wrote: > > Would it be possible to keep get() unchanged, with a default > > behaviour, plus > > a warning? Otherwise everybody (assuming everybody gets type void*) > > will > > have to update their LLVM passes, and either maintain two versions > > of the > > passes or require their clients to use a certain LLVM version. > > AFAIK API compatibility is not guaranteed across LLVM point releases, > so I believe clients are tied to a specific version of LLVM in any case. > > > Then passes > > could be "address-space-safe" or not. If the default parameter > > value for > > get() could be a unique ID for "not specified" instead of "the default > > address space", then one should even be able to continue to use get() > > isntead of sth like getQual(...). > > The reason for the change was to make it absolutely clear in the > source where address space qualifiers are preserved/added or stripped > from the pointer type. Allowing clients to use get() and then > dynamically track "undefined" address spaces under the hood is > counter to this goal.Informally, what I'd like to have is getUnqual() semantics as default for get(), thus giving you the same safety properties but without having to change all occurrences. If clients do handle address spaces, they could use getQual(...) and getUnqual(). I don't see how this would be counter to your goals. If a module with address spaces comes along, the pass could still abort and thell the user that it doesn't know how to handle this, which would give users a complete incremental upgrade path. I know that this approach might not really encourage developers to consider address space issues. Are they important and widespread enough that everybody should (or is proper address space handling trivial enough)? Torvald