search for: devirtualizations

Please send any comments. As mentioned at the end I will follow up with some patches as soon as they are cleaned up and I create some test cases. RFC: Safe Whole Program Devirtualization Enablement =================================================== High Level Summary ------------------ The goal of the changes described in this RFC is to support aggressive Whole Program Devirtualization without

On Wed, Oct 13, 2010 at 12:45 AM, Nick Lewycky <nicholas at mxc.ca> wrote: > Kenneth Uildriks wrote: >>> >>> You're right, I hadn't thought this through. The whole point of making >>> them >>> local is to say that "I'm sure these callees won't modify that memory" >>> regardless of what functions actually get called,

Vitor Luis Menezes wrote: > Hello all, > > Our compilers class has been using LLVM, and a partner and I decided to > implement devirtualization of virtual C++ calls in LLVM as a class > project. We quickly realized that existing debug metadata generated by > Clang didn't give us enough info to (precisely) implement this, and as > such have already begun modifying Clang to

Chandler et al, I have been playing with the new PM pipeline, being particularly interested in how it can handle devirtualization. Now, I discovered what I believe is a "regression" vs old PM on a rather simple one-translation-unit testcase. clang is able to devirtualize it with -O3 and fails to do so with -fexperimental-new-pass-manager added. It looks like a pipeline issue,

Kenneth Uildriks wrote: > On Wed, Oct 13, 2010 at 12:45 AM, Nick Lewycky<nicholas at mxc.ca> wrote: >> Kenneth Uildriks wrote: >>>> >>>> You're right, I hadn't thought this through. The whole point of making >>>> them >>>> local is to say that "I'm sure these callees won't modify that memory" >>>>

Yes, this looks broken in the new PM. The DevirtSCCRepeatedPass::run method first scans the functions in the SCC to collect value handles for indirect calls, runs the CGSCC pass pipeline and then checks if any of the call value handles now point to a direct call, in which case it runs the pipeline again (which should inline the devirtualized call) . The problem is scanning the initial SCC for

Hi! I have a question about whole program devirtualization pass. According to my understanding devirtualization is performed only for the classes that have hidden LTO visibility and this visibility is controlled by attributes in the source level or command line options. So visibility analysis is currently performed only in the front-end. But LLVM has LTO internalization pass that uses

On Oct 13, 2010, at 4:35 AM, Kenneth Uildriks wrote: > On Wed, Oct 13, 2010 at 12:45 AM, Nick Lewycky <nicholas at mxc.ca> wrote: >> Kenneth Uildriks wrote: >>>> >>>> You're right, I hadn't thought this through. The whole point of making >>>> them >>>> local is to say that "I'm sure these callees won't modify

Hello all, Our compilers class has been using LLVM, and a partner and I decided to implement devirtualization of virtual C++ calls in LLVM as a class project. We quickly realized that existing debug metadata generated by Clang didn't give us enough info to (precisely) implement this, and as such have already begun modifying Clang to insert such metadata. However, for devirtualization we also

Kenneth Uildriks wrote: >> You're right, I hadn't thought this through. The whole point of making them >> local is to say that "I'm sure these callees won't modify that memory" >> regardless of what functions actually get called, even indirectly. We can't >> know that they won't modify the vptr in advance, so invariant doesn't work

On Wed, Oct 13, 2010 at 11:16 PM, Nick Lewycky <nicholas at mxc.ca> wrote: > Kenneth Uildriks wrote: >> >> On Wed, Oct 13, 2010 at 12:45 AM, Nick Lewycky<nicholas at mxc.ca>  wrote: >>> >>> Kenneth Uildriks wrote: >>>>> >>>>> You're right, I hadn't thought this through. The whole point of making >>>>>

On Oct 11, 2010, at 9:12 AM, Kenneth Uildriks wrote: > 3. The front-end, recognizing that scribbling on an instance's vtbl > pointer has undefined results, eliminated the loads of the vtbl > pointer and replaced them with @classvtbl.TestVirtual. This would > allow devirtualization within a function at least, but (I think) would > do less to allow analysis to spot

On Tue, Feb 03, 2015 at 04:03:45PM -0800, Sean Silva wrote: > One other thing: if this can be used for control-flow integrity, I assume > it has to have good knowledge of the available indirect call targets. Could > we also use this information for devirtualization? I would expect so. If a bitset contains only one element, we should be able to teach the lowering pass to simply test that

Hi Peter, Thanks for the reply. I agree that the base class vtable may be not referenced by a derived class. However, the vtable of a derived class has to reference its parent type_info, and so having type_info internalized means that the class is final, doesn’t it? Thanks, Nikolai From: Peter Collingbourne [mailto:peter at pcc.me.uk] Sent: Wednesday, December 6, 2017 4:36 AM To: Gainullin,

Sounds like it works! Basically, adding these extra strip.invariant.group calls before pointer comparisons breaks the transform that was problematic. Presumably, clang would only strip invariant groups from pointers to dynamic types before casting them or using them in a comparison, so that the value equivalence optimization still works in the general case. The proposal trades value equivalence

Hello, I've stumbled upon the following behavior in branches/release_35 (as of 218689) under ubuntu 14.04 LTS amd64: whenever I include the (system-wise) gnu iostream header, clang++ stops devirtualizing the following code: #if BREAKAGE_ENSUES #include <iostream> #endif struct Base { virtual int foo() const = 0; }; struct A : Base { int a; A(const int a) : a(a) { } int foo() const

> You're right, I hadn't thought this through. The whole point of making them > local is to say that "I'm sure these callees won't modify that memory" > regardless of what functions actually get called, even indirectly. We can't > know that they won't modify the vptr in advance, so invariant doesn't work > here. Making it non-local just means

On Sun, Jun 19, 2016 at 12:01 AM, Sanjoy Das <sanjoy at playingwithpointers.com > wrote: > Hi David, > > Xinliang David Li wrote: > >> I believe it is primarily used for ordering the visitation of > CallSCC's (i.e. SCC's in the "call graph"). > > This is what it can do -- but what benefit does it provide? > > One benefit is that once you

I took the output of clang, simplified it, and used it as a testbase. Essentially, there is one class with one virtual function; I create an instance and call the virtual method all in one function: ; The TestVirtual class vtbl @classvtbl.TestVirtual = constant %classvtbltype.TestVirtual { ; Pointers to the virtual methods for the TestVirtual class ... } ; ... define i32 @main() nounwind { ;

On Oct 14, 2010, at 5:08 AM, Kenneth Uildriks wrote: > On Wed, Oct 13, 2010 at 11:16 PM, Nick Lewycky <nicholas at mxc.ca> wrote: >> Kenneth Uildriks wrote: >>> >>> On Wed, Oct 13, 2010 at 12:45 AM, Nick Lewycky<nicholas at mxc.ca> wrote: >>>> >>>> Kenneth Uildriks wrote: >>>>>> >>>>>> You're