Chris Lattner via llvm-dev
2016-Oct-26 05:48 UTC
[llvm-dev] RFC: Absolute or "fixed address" symbols as immediate operands
Responding to both of your emails in one, sorry for the delay:> On Oct 25, 2016, at 11:20 AM, Peter Collingbourne <peter at pcc.me.uk> wrote: > I think there are a couple of additional considerations we should make here: > What are we trying to model? To me it's clear that GlobalConstant is for modelling integers, not pointers. That alone may not necessarily be enough to motivate a representational change, but…I understand where you’re coming from, but I think we’re modeling three different things, and disagreeing about how to clump them together. The three things I see in flight are: 1) typical globals that are laid out in some unknown way in the address space. 2) globals that may be tied to a specific knowable address range due to a limited compilation model (e.g. a deeply embedded core) that fits into an immedaite range (e.g. 0…255, 0…65536, etc). 3) Immediates that are treated as symbolic for CFI’s perspective (so they can’t just be used as a literal immediate) that are resolved at link time, but are known to have limited range. There is also "4) immediates with an obvious known value”, but those are obviously ConstantInt’s and not interesting to discuss here. The design I’m arguing for is to clump #2 and #3 into the same group. This can be done one of two different ways, but both ways use the same “declaration side” reference, which has a !range metadata attached to it. The three approaches I see are: a) Introduce a new GlobalConstant definition, whose value is the concrete address that the linker should resolve. b) Use an alias as the definition, whose body is a ptrtoint constant of the same value. c) Use a zero size globalvariable with a range metadata specifying the exact address decided. I’m not very knowledgable about why approach b won’t work, but if it could, it seems preferable because it fits in with our current model. After that, approach C seems like a nice fallback because it again doesn’t require major extensions to our model. Finally, approach A seems like the most explicit model, but has the disadvantage of introducing a new IR concept that will be rarely used (and thus prone to bugs due to it not being widely tested).> If we make our representation fit the model, does that improve the quality of the code? There's clearly been a long standing assumption that GlobalValues are of pointer type. Breaking that assumption has in fact found potential bugs (see e.g. my changes to ValueTracking.cpp in D25930, as well as D25917 which was a requirement for the representational change), and seems like it may help prevent bugs in the future, so I'd say that the answer is most likely yes.I’d argue the other side of it. The quality of the code is higher if we have invariants (like all globals are pointers) because that simplifies assumptions by eliminating cases where “is a pointer” appears to be true, but isn’t actually true in all cases. I’m not an expert on CFI or how widely it will ultimately impact the compiler hacker consciousness, but I’m pretty sure that the current model for globals and functions will remain more prominent. If you choose to break this invariant, you’ll be continually swimming upstream against assumptions made throughout the compiler, both in code written today but also in code written in the future. On Oct 25, 2016, at 6:52 PM, Peter Collingbourne <peter at pcc.me.uk> wrote:> > So, to summarise the overall consensus on this thread: > - We should introduce a GlobalConstant class which supports definitions and declarationsWhy would globalconstant need to support declarations? Seems like an external global should be able to handle this case.> - It should derive from GlobalValue > - No type changes for GlobalValue (i.e. still required to be pointer type) > - To communicate the range we should use !range metadata and support it on GlobalConstant as well as GlobalVariable > > Although I am not convinced that this is the right representation I appear to be in the minority here, so if this seems reasonable to folks I will go ahead and implement it.I’m not trying to steamroll you over: what is your specific concern? -Chris -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20161025/1d590327/attachment.html>
Peter Collingbourne via llvm-dev
2016-Oct-26 08:34 UTC
[llvm-dev] RFC: Absolute or "fixed address" symbols as immediate operands
On Tue, Oct 25, 2016 at 10:48 PM, Chris Lattner <clattner at apple.com> wrote:> Responding to both of your emails in one, sorry for the delay: > > On Oct 25, 2016, at 11:20 AM, Peter Collingbourne <peter at pcc.me.uk> wrote: > I think there are a couple of additional considerations we should make > here: > > - What are we trying to model? To me it's clear that GlobalConstant is > for modelling integers, not pointers. That alone may not necessarily be > enough to motivate a representational change, but… > > I understand where you’re coming from, but I think we’re modeling three > different things, and disagreeing about how to clump them together. The > three things I see in flight are: > > 1) typical globals that are laid out in some unknown way in the address > space. > 2) globals that may be tied to a specific knowable address range due to a > limited compilation model (e.g. a deeply embedded core) that fits into an > immedaite range (e.g. 0…255, 0…65536, etc). > 3) Immediates that are treated as symbolic for CFI’s perspective (so they > can’t just be used as a literal immediate) that are resolved at link time, > but are known to have limited range. > > There is also "4) immediates with an obvious known value”, but those are > obviously ConstantInt’s and not interesting to discuss here. > > The design I’m arguing for is to clump #2 and #3 into the same group. >I am not sure if this is sound if we want the no-alias assumption (see also below) to hold for #2 but not for #3.> This can be done one of two different ways, but both ways use the same > “declaration side” reference, which has a !range metadata attached to it. > The three approaches I see are: > > a) Introduce a new GlobalConstant definition, whose value is the concrete > address that the linker should resolve. > b) Use an alias as the definition, whose body is a ptrtoint constant of > the same value. > c) Use a zero size globalvariable with a range metadata specifying the > exact address decided. > > I’m not very knowledgable about why approach b won’t work, but if it > could, it seems preferable because it fits in with our current model. >b would work in that it would give us the right bits in the object file, but it would be a little odd to use a different type for declarations as for definitions. That said, I don't have a strong objection to it. After that, approach C seems like a nice fallback because it again doesn’t> require major extensions to our model. Finally, approach A seems like the > most explicit model, but has the disadvantage of introducing a new IR > concept that will be rarely used (and thus prone to bugs due to it not > being widely tested). > > > - If we make our representation fit the model, does that improve the > quality of the code? There's clearly been a long standing assumption that > GlobalValues are of pointer type. Breaking that assumption has in fact > found potential bugs (see e.g. my changes to ValueTracking.cpp in D25930, > as well as D25917 which was a requirement for the representational change), > and seems like it may help prevent bugs in the future, so I'd say that the > answer is most likely yes. > > I’d argue the other side of it. The quality of the code is higher if we > have invariants (like all globals are pointers) because that simplifies > assumptions by eliminating cases where “is a pointer” appears to be true, > but isn’t actually true in all cases. >We'd still be able to have an "is a pointer" invariant, but on a specific subset of globals. In practice I'd expect that a frontend that chooses to make that assumption can use GlobalPointer in place of GlobalValue.> I’m not an expert on CFI or how widely it will ultimately impact the > compiler hacker consciousness, but I’m pretty sure that the current model > for globals and functions will remain more prominent. If you choose to > break this invariant, you’ll be continually swimming upstream against > assumptions made throughout the compiler, both in code written today but > also in code written in the future. >I think this is as least as likely to be true in the case where we do choose to use pointer modelling, as those assumptions are going to exist no matter what representation we choose, at least until they are found and fixed. The difference is that when assumptions are broken, they will be more likely to break loudly (e.g. casting assertion failures) as opposed to subtly as could have happened with the non-null assumption in ValueTracking. CFI will have full integration testing on supported platforms, and has been deployed in Chrome on Linux since August, so at least the important known use cases should continue to work. The unimportant use cases may not, but that seems like it could be the case for any IR feature. You can see for yourself from D25930 that (relatively speaking) very few places in the entire codebase need to care about this at the type system level. I was in fact surprised at how little code I needed to change for an assumption that has apparently existed since 2001. Granted this doesn't reveal non-type-system-level assumptions, but as I mentioned those assumptions would exist anyway. On Oct 25, 2016, at 6:52 PM, Peter Collingbourne <peter at pcc.me.uk> wrote:> > > So, to summarise the overall consensus on this thread: > - We should introduce a GlobalConstant class which supports definitions > and declarations > > > Why would globalconstant need to support declarations? Seems like an > external global should be able to handle this case. >An external globalvariable? I am not sure how to reconcile this with your comment on D25878:> LLVM IR global variables should always be assumable that they don't alias.I'm thinking of the case where we have two globalconstants which happen to have the same value. - It should derive from GlobalValue> - No type changes for GlobalValue (i.e. still required to be pointer type) > - To communicate the range we should use !range metadata and support it on > GlobalConstant as well as GlobalVariable > > Although I am not convinced that this is the right representation I appear > to be in the minority here, so if this seems reasonable to folks I will go > ahead and implement it. > > > I’m not trying to steamroll you over: what is your specific concern? >My specific concern is pointer modeling. I think Chandler put it well in his most recent mail. Thanks, -- -- Peter -------------- next part -------------- An HTML attachment was scrubbed... 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Chandler Carruth via llvm-dev
2016-Oct-26 17:10 UTC
[llvm-dev] RFC: Absolute or "fixed address" symbols as immediate operands
To what Reid said, I'm not really worried about impact on the middle end of any of this. We can handle the code changes, etc. I agree with Chris about what we're trading off here: On Tue, Oct 25, 2016 at 10:48 PM Chris Lattner via llvm-dev < llvm-dev at lists.llvm.org> wrote:> I’d argue the other side of it. The quality of the code is higher if we > have invariants (like all globals are pointers) because that simplifies > assumptions by eliminating cases where “is a pointer” appears to be true, > but isn’t actually true in all cases. I’m not an expert on CFI or how > widely it will ultimately impact the compiler hacker consciousness, but I’m > pretty sure that the current model for globals and functions will remain > more prominent. If you choose to break this invariant, you’ll be > continually swimming upstream against assumptions made throughout the > compiler, both in code written today but also in code written in the future. >I agree that mental assumptions the developers on the middle end hold are the primary challenge here. But I think we are going to run into challenges either way. If the type of these entities is an integer, we will have a non-pointer global, yes. But as Peter points out, this is caught effectively by asserts in the cast infrastructure and other programming aids. Essentially, the checking of LLVM's type system helps protect the random middle end developer from getting this wrong. On the other hand, if the type of these entities remains consistently pointers, we will still break assumptions that middle end developers routinely make about pointers to globals: - They aren't dereferencable - They aren't aligned - They may be null - The difference between them might not be representable in a pointer-sized-integer In essence, their *values* won't behave like pointers even if we make the LLVM IR type a pointer. So the wrong assumption will shift from an IR type system error to a value error. I would generally much prefer the LLVM IR's type system catch this kind of error. Even if these wrong assumptions about the values are much less common, I would prefer the more common but easily caught type system error. To Rafael's point, while I agree that at the object file level these are indeed addresses, I personally am much more interested in the IR modeling things in ways convenient to the middle end optimizer than to the linker. And there, the above seems like the dominant tradeoff. Anyways, if Reid, Chris, and Rafael all strongly feel like keeping the types consistent is actually the right tradeoff, I don't want to stand in the way. So far, I just find the arguments for why this is the right tradeoff unconvincing. -Chandler PS: In case it isn't clear, I'm totally fine with having the range metadata available for the case where globals are mapped into very specific regions for bare metal / embedded architectures, but *should* be treated as actual addresses of objects that can be loaded and stored through. And those seem unambiguously like they should be pointers. But that seems like a separate use case and discussion... -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20161026/f22db89c/attachment.html>
Philip Reames via llvm-dev
2016-Oct-26 22:48 UTC
[llvm-dev] RFC: Absolute or "fixed address" symbols as immediate operands
On 10/26/2016 10:10 AM, Chandler Carruth via llvm-dev wrote:> To what Reid said, I'm not really worried about impact on the middle > end of any of this. We can handle the code changes, etc. > > I agree with Chris about what we're trading off here: > > On Tue, Oct 25, 2016 at 10:48 PM Chris Lattner via llvm-dev > <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote: > > I’d argue the other side of it. The quality of the code is higher > if we have invariants (like all globals are pointers) because that > simplifies assumptions by eliminating cases where “is a pointer” > appears to be true, but isn’t actually true in all cases. I’m not > an expert on CFI or how widely it will ultimately impact the > compiler hacker consciousness, but I’m pretty sure that the > current model for globals and functions will remain more > prominent. If you choose to break this invariant, you’ll be > continually swimming upstream against assumptions made throughout > the compiler, both in code written today but also in code written > in the future. > > > I agree that mental assumptions the developers on the middle end hold > are the primary challenge here. But I think we are going to run into > challenges either way. > > If the type of these entities is an integer, we will have a > non-pointer global, yes. But as Peter points out, this is caught > effectively by asserts in the cast infrastructure and other > programming aids. Essentially, the checking of LLVM's type system > helps protect the random middle end developer from getting this wrong. > > On the other hand, if the type of these entities remains consistently > pointers, we will still break assumptions that middle end developers > routinely make about pointers to globals: > - They aren't dereferencable > - They aren't aligned > - They may be null > - The difference between them might not be representable in a > pointer-sized-integer > > In essence, their *values* won't behave like pointers even if we make > the LLVM IR type a pointer. So the wrong assumption will shift from an > IR type system error to a value error. I would generally much prefer > the LLVM IR's type system catch this kind of error. Even if these > wrong assumptions about the values are much less common, I would > prefer the more common but easily caught type system error. > > > To Rafael's point, while I agree that at the object file level these > are indeed addresses, I personally am much more interested in the IR > modeling things in ways convenient to the middle end optimizer than to > the linker. And there, the above seems like the dominant tradeoff. > > > Anyways, if Reid, Chris, and Rafael all strongly feel like keeping the > types consistent is actually the right tradeoff, I don't want to stand > in the way. So far, I just find the arguments for why this is the > right tradeoff unconvincing.I agree with Chandler here on pretty much all of this (including the willingness to be ignored if consensus goes the other way.)> > -Chandler > > > PS: In case it isn't clear, I'm totally fine with having the range > metadata available for the case where globals are mapped into very > specific regions for bare metal / embedded architectures, but *should* > be treated as actual addresses of objects that can be loaded and > stored through. And those seem unambiguously like they should be > pointers. But that seems like a separate use case and discussion... > > > _______________________________________________ > LLVM Developers mailing list > llvm-dev at lists.llvm.org > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20161026/7b14d16e/attachment.html>
Chris Lattner via llvm-dev
2016-Oct-27 04:43 UTC
[llvm-dev] RFC: Absolute or "fixed address" symbols as immediate operands
On Oct 26, 2016, at 10:10 AM, Chandler Carruth <chandlerc at google.com> wrote:> > To what Reid said, I'm not really worried about impact on the middle end of any of this. We can handle the code changes, etc. > > I agree with Chris about what we're trading off here: > > On Tue, Oct 25, 2016 at 10:48 PM Chris Lattner via llvm-dev <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote: > I’d argue the other side of it. The quality of the code is higher if we have invariants (like all globals are pointers) because that simplifies assumptions by eliminating cases where “is a pointer” appears to be true, but isn’t actually true in all cases. I’m not an expert on CFI or how widely it will ultimately impact the compiler hacker consciousness, but I’m pretty sure that the current model for globals and functions will remain more prominent. If you choose to break this invariant, you’ll be continually swimming upstream against assumptions made throughout the compiler, both in code written today but also in code written in the future. > > I agree that mental assumptions the developers on the middle end hold are the primary challenge here. But I think we are going to run into challenges either way. > > If the type of these entities is an integer, we will have a non-pointer global, yes. But as Peter points out, this is caught effectively by asserts in the cast infrastructure and other programming aids. Essentially, the checking of LLVM's type system helps protect the random middle end developer from getting this wrong. > > On the other hand, if the type of these entities remains consistently pointers, we will still break assumptions that middle end developers routinely make about pointers to globals: > - They aren't dereferencable > - They aren't aligned > - They may be null > - The difference between them might not be representable in a pointer-sized-integerAren’t all these true of “inttoptr’d” integer constants already? This is already part of the model for things that are PointerType’s, so I don’t see how either resolution would change that. -Chris -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20161026/958018e8/attachment.html>
Chris Lattner via llvm-dev
2016-Oct-27 04:48 UTC
[llvm-dev] RFC: Absolute or "fixed address" symbols as immediate operands
On Oct 26, 2016, at 1:34 AM, Peter Collingbourne <peter at pcc.me.uk> wrote:> On Tue, Oct 25, 2016 at 10:48 PM, Chris Lattner <clattner at apple.com <mailto:clattner at apple.com>> wrote: > Responding to both of your emails in one, sorry for the delay: > >> On Oct 25, 2016, at 11:20 AM, Peter Collingbourne <peter at pcc.me.uk <mailto:peter at pcc.me.uk>> wrote: >> I think there are a couple of additional considerations we should make here: >> What are we trying to model? To me it's clear that GlobalConstant is for modelling integers, not pointers. That alone may not necessarily be enough to motivate a representational change, but… > I understand where you’re coming from, but I think we’re modeling three different things, and disagreeing about how to clump them together. The three things I see in flight are: > > 1) typical globals that are laid out in some unknown way in the address space. > 2) globals that may be tied to a specific knowable address range due to a limited compilation model (e.g. a deeply embedded core) that fits into an immedaite range (e.g. 0…255, 0…65536, etc). > 3) Immediates that are treated as symbolic for CFI’s perspective (so they can’t just be used as a literal immediate) that are resolved at link time, but are known to have limited range. > > There is also "4) immediates with an obvious known value”, but those are obviously ConstantInt’s and not interesting to discuss here. > > The design I’m arguing for is to clump #2 and #3 into the same group. > > I am not sure if this is sound if we want the no-alias assumption (see also below) to hold for #2 but not for #3. > > This can be done one of two different ways, but both ways use the same “declaration side” reference, which has a !range metadata attached to it. The three approaches I see are: > > a) Introduce a new GlobalConstant definition, whose value is the concrete address that the linker should resolve. > b) Use an alias as the definition, whose body is a ptrtoint constant of the same value. > c) Use a zero size globalvariable with a range metadata specifying the exact address decided. > > I’m not very knowledgable about why approach b won’t work, but if it could, it seems preferable because it fits in with our current model. > > b would work in that it would give us the right bits in the object file, but it would be a little odd to use a different type for declarations as for definitions. That said, I don't have a strong objection to it.I can understand what you’re saying here, but this is already the case for aliases. You can never have a “declaration side” for an alias that is an alias (you have to use an external global variable or a function with no body). From the discussion over the last day it sounds to me that “b” is the best approach, except for the (significant) annoyance that these things can be possibly aliased. However, I don’t understand how this works in practice today for aliases. By their very name, they are *all about* introducing aliases, so how is AA allowed to assume that two external global variable references are unaliased anyway? One may be resolved as an alias to the other afterall, completely independent of your proposal. -Chris -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20161026/8fc5b1d0/attachment.html>
Peter Collingbourne via llvm-dev
2016-Oct-27 05:39 UTC
[llvm-dev] RFC: Absolute or "fixed address" symbols as immediate operands
Re-adding list. On Wed, Oct 26, 2016 at 10:38 PM, Peter Collingbourne <peter at pcc.me.uk> wrote:> > > On Wed, Oct 26, 2016 at 9:43 PM, Chris Lattner <clattner at apple.com> wrote: > >> On Oct 26, 2016, at 10:10 AM, Chandler Carruth <chandlerc at google.com> >> wrote: >> >> >> To what Reid said, I'm not really worried about impact on the middle end >> of any of this. We can handle the code changes, etc. >> >> I agree with Chris about what we're trading off here: >> >> On Tue, Oct 25, 2016 at 10:48 PM Chris Lattner via llvm-dev < >> llvm-dev at lists.llvm.org> wrote: >> >>> I’d argue the other side of it. The quality of the code is higher if we >>> have invariants (like all globals are pointers) because that simplifies >>> assumptions by eliminating cases where “is a pointer” appears to be true, >>> but isn’t actually true in all cases. I’m not an expert on CFI or how >>> widely it will ultimately impact the compiler hacker consciousness, but I’m >>> pretty sure that the current model for globals and functions will remain >>> more prominent. If you choose to break this invariant, you’ll be >>> continually swimming upstream against assumptions made throughout the >>> compiler, both in code written today but also in code written in the future. >>> >> >> I agree that mental assumptions the developers on the middle end hold are >> the primary challenge here. But I think we are going to run into challenges >> either way. >> >> If the type of these entities is an integer, we will have a non-pointer >> global, yes. But as Peter points out, this is caught effectively by asserts >> in the cast infrastructure and other programming aids. Essentially, the >> checking of LLVM's type system helps protect the random middle end >> developer from getting this wrong. >> >> On the other hand, if the type of these entities remains consistently >> pointers, we will still break assumptions that middle end developers >> routinely make about pointers to globals: >> - They aren't dereferencable >> - They aren't aligned >> - They may be null >> - The difference between them might not be representable in a >> pointer-sized-integer >> >> >> Aren’t all these true of “inttoptr’d” integer constants already? This is >> already part of the model for things that are PointerType’s, so I don’t see >> how either resolution would change that. >> > > For at least assumptions 1 and 3 this may be true right now for most > values of type PointerType, but not necessarily for GlobalVariables of type > PointerType. > > Thanks, > -- > -- > Peter >-- -- Peter -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20161026/20c06e4c/attachment.html>
Peter Collingbourne via llvm-dev
2016-Oct-29 02:01 UTC
[llvm-dev] RFC: Absolute or "fixed address" symbols as immediate operands
On Wed, Oct 26, 2016 at 10:39 PM, Peter Collingbourne <peter at pcc.me.uk> wrote:> Re-adding list. > > On Wed, Oct 26, 2016 at 10:38 PM, Peter Collingbourne <peter at pcc.me.uk> > wrote: > >> >> >> On Wed, Oct 26, 2016 at 9:43 PM, Chris Lattner <clattner at apple.com> >> wrote: >> >>> On Oct 26, 2016, at 10:10 AM, Chandler Carruth <chandlerc at google.com> >>> wrote: >>> >>> >>> To what Reid said, I'm not really worried about impact on the middle end >>> of any of this. We can handle the code changes, etc. >>> >>> I agree with Chris about what we're trading off here: >>> >>> On Tue, Oct 25, 2016 at 10:48 PM Chris Lattner via llvm-dev < >>> llvm-dev at lists.llvm.org> wrote: >>> >>>> I’d argue the other side of it. The quality of the code is higher if >>>> we have invariants (like all globals are pointers) because that simplifies >>>> assumptions by eliminating cases where “is a pointer” appears to be true, >>>> but isn’t actually true in all cases. I’m not an expert on CFI or how >>>> widely it will ultimately impact the compiler hacker consciousness, but I’m >>>> pretty sure that the current model for globals and functions will remain >>>> more prominent. If you choose to break this invariant, you’ll be >>>> continually swimming upstream against assumptions made throughout the >>>> compiler, both in code written today but also in code written in the future. >>>> >>> >>> I agree that mental assumptions the developers on the middle end hold >>> are the primary challenge here. But I think we are going to run into >>> challenges either way. >>> >>> If the type of these entities is an integer, we will have a non-pointer >>> global, yes. But as Peter points out, this is caught effectively by asserts >>> in the cast infrastructure and other programming aids. Essentially, the >>> checking of LLVM's type system helps protect the random middle end >>> developer from getting this wrong. >>> >>> On the other hand, if the type of these entities remains consistently >>> pointers, we will still break assumptions that middle end developers >>> routinely make about pointers to globals: >>> - They aren't dereferencable >>> - They aren't aligned >>> - They may be null >>> - The difference between them might not be representable in a >>> pointer-sized-integer >>> >>> >>> Aren’t all these true of “inttoptr’d” integer constants already? This >>> is already part of the model for things that are PointerType’s, so I don’t >>> see how either resolution would change that. >>> >> >> For at least assumptions 1 and 3 this may be true right now for most >> values of type PointerType, but not necessarily for GlobalVariables of type >> PointerType. >> >I think that before conceding my point I would like to see a response to this. Thanks, -- -- Peter -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20161028/c680352f/attachment.html>
Apparently Analagous Threads
- RFC: Absolute or "fixed address" symbols as immediate operands
- RFC: Absolute or "fixed address" symbols as immediate operands
- RFC: Absolute or "fixed address" symbols as immediate operands
- RFC: Absolute or "fixed address" symbols as immediate operands
- RFC: Absolute or "fixed address" symbols as immediate operands