similar to: [LLVMdev] Clang devirtualization proposal

Hi Piotr, You may be interested in a recent patch I posted: http://reviews.llvm.org/D11043 This patch addresses a de-virtualization case that I’m not sure would be handled by your current proposal, namely that of a virtual call where the ‘this’ object is a global variable. For example: struct A { A(); virtual void foo(); }; void g(A * a) { a->foo(); } A a; int main()

HI, Yep, our proposal doesn't cover it, because this load ; icmp ; assume; will land global initilizer function, and main will not see it. At least if foo would be called multiple times, then we would only have one load from vtable, but unfortunatelly we will not be able to inline, or make direct call to it with this approach. I think that this case is rare enough to solve it right now. Piotr

On Thu, Jul 23, 2015 at 11:42 AM, Piotr Padlewski <prazek at google.com> wrote: > HI, > Yep, our proposal doesn't cover it, because this load ; icmp ; assume; > will land global initilizer function, and main will not see it. > At least if foo would be called multiple times, then we would only have > one load from vtable, but unfortunatelly we will not be able to inline,

Hi Piotr, Thanks for posting this! First, a question. When you say, regarding i8* @llvm.invariant.group.barrier(i8*): "Required to handle destructors, placement new and std::launder. Call of this function will be put on the end of each of this functions" I completely understand placement new and std::launder. I don't understand destructors, could you explain? Also, am I correct

On Sat, Jul 25, 2015 at 12:39 PM, Hal Finkel <hfinkel at anl.gov> wrote: > Hi Piotr, > > Thanks for posting this! First, a question. When you say, regarding i8* > @llvm.invariant.group.barrier(i8*): > > "Required to handle destructors, placement new and std::launder. Call of > this function will be put on the end of each of this functions" > > I

Ok, replying anew now that I understand why reasoning about abstract locations for each object doesn't work. The general idea of describing a set of load and stores which belong to a particular invariant group seems reasonable. I've got some questions/comments on the specifics, but the overall direction seems entirely workable for the specific problem you're trying to solve.

Having read through the proposal, I feel like I missing some of the background to understand the problem you're trying to solve. My mental model is that construction of an object creates a new abstract location in an infinite heap with each object infinitely far apart. Destruction of the object destroys the abstract location. As a result, destructing one object and constructing another

Hi folks, here is a link to the proposal that we've been working on lately: https://docs.google.com/document/d/16GVtCpzK8sIHNc2qZz6RN8amICNBt vjWUod2SujZVEo/edit?usp=sharing But for the record, I also paste it here. Feedback will be really appreciated!

2017-04-01 15:59 GMT+02:00 Piotr Padlewski <piotr.padlewski at gmail.com>: > > > 2017-03-31 23:20 GMT+02:00 Sanjoy Das <sanjoy at playingwithpointers.com>: > >> Hi Piotr, >> >> On March 31, 2017 at 1:07:12 PM, Piotr Padlewski >> (piotr.padlewski at gmail.com) wrote: >> > [snip] >> > Do I understand it correctly, that it is legal to

> On Mar 19, 2018, at 7:27 PM, Piotr Padlewski via cfe-dev <cfe-dev at lists.llvm.org> wrote: > > Hi folks, > > here is a link to the proposal that we've been working on lately: > https://docs.google.com/document/d/16GVtCpzK8sIHNc2qZz6RN8amICNBtvjWUod2SujZVEo/edit?usp=sharing

Hi Piotr, I think makes sense. Modulo bitcasts, the invariant is identified by a particular pointer SSA value. Given that you can't sensibly have two nonequivalent invariants associated with the same pointer SSA value simultaneously, there's no need to also identify the invariant with a metadata string as well. When we need a new "identifier" for the pointed-to value, we

Hi all, I would like to propose a new way clang would decorate vtable loads in order to handle devirtualization better. I've added *llvm-dev* also, because this can start a discussion about changing invariant.group to just invariant. PDF version of this RFC can be found here: https://drive.google.com/file/d/0B72TmzNsY6Z8ZmpOUnB5dDZfSFU/view?usp=sharing Background: Initial old design:

Hi Piotr, On March 31, 2017 at 1:07:12 PM, Piotr Padlewski (piotr.padlewski at gmail.com) wrote: > [snip] > Do I understand it correctly, that it is legal to do the hoist because all > of the instructions above %vtable does not throw? Yes, I think you're right.  HeaderMayThrow is a conservative approximation, and the conservativeness is biting us here. > Are there any plans to

Hi folks, please check out our RFC: Supported Optimizations attribute https://docs.google.com/document/d/1s0n-JVaSNML1Z9SCZVg2bgisxswIJAK2Tp9DahucW10/edit?usp=sharing Pasting it here for the record: RFC: supported_optimizations attribute Piotr Padlewski - piotr.padlewski at gmail.com Krzysztof Pszeniczny - kpszeniczny at google.com December 2018 Introduction Sometimes a possible class of

Hi Piotr, On Thu, May 4, 2017 at 6:44 AM, Piotr Padlewski <piotr.padlewski at gmail.com> wrote: > Also, Sanjoy proposed to mark invariant.group features as experimental, so > we will not be afraid to break behavior of frontends that already use it. > > Right now I am pretty sure that clang is the only one that curently uses it > (and not by default). Firstly, yes, I think we

2017-01-26 3:28 GMT+01:00 Richard Smith <richard at metafoo.co.uk>: > On 25 January 2017 at 15:03, Hal Finkel via cfe-dev < > cfe-dev at lists.llvm.org> wrote: > >> Hi Piotr, >> >> I think makes sense. Modulo bitcasts, the invariant is identified by a >> particular pointer SSA value. Given that you can't sensibly have two >> nonequivalent

2017-01-26 15:41 GMT+01:00 Hal Finkel <hfinkel at anl.gov>: > > On 01/26/2017 06:44 AM, Piotr Padlewski wrote: > > > > 2017-01-26 3:28 GMT+01:00 Richard Smith <richard at metafoo.co.uk>: > >> On 25 January 2017 at 15:03, Hal Finkel via cfe-dev < >> cfe-dev at lists.llvm.org> wrote: >> >>> Hi Piotr, >>> >>> I think

Hi all, I have a question about dereferenceable metadata on load instruction. I have a patch (https://reviews.llvm.org/D31539) for LICM that hoists loads with !invariant.group. The motivation example is devirtualization: struct A { virtual void foo(); }; int bar(); void indirect(A &a) { while(bar()) a.foo(); } With -O2 -fstrict-vtable-pointers we get: define void

2018-03-29 18:01 GMT+02:00 John McCall <rjmccall at apple.com>: > On Mar 29, 2018, at 9:12 AM, Piotr Padlewski <piotr.padlewski at gmail.com> > wrote: > 2018-03-28 23:23 GMT+02:00 John McCall <rjmccall at apple.com>: >> >> On Mar 19, 2018, at 7:27 PM, Piotr Padlewski via cfe-dev < >> cfe-dev at lists.llvm.org> wrote: >> *Note that adding

Hi folks, I would like to ask for some help with handling invariant.group metadata for pointer comparison. Currently, we have a problem with devirtualization of this code: void compare() { A* a = new A; a->foo(); A* b = new(a) B; if (a == b) { b->foo(); } } Now because it is legal to replace b with an in the branch the vtable load will use old pointer operand