search for: devirtualize

...given pointer is associated with the given type identifier (https://llvm.org/docs/LangRef.html#llvm-type-test-intrinsic). It is currently inserted only for classes with hidden LTO visibility as the implication of this sequence is that we have full visibility of that type’s class hierarchy, and may devirtualize the call based on that knowledge. This assumption is not valid if the class does not have hidden LTO visibility. In order to drive later devirtualization, we still need the type compatibility information provided by the llvm.type.test, but want to delay a decision on whether it is valid to assume...

...>>> can't >>> know that they won't modify the vptr in advance, so invariant doesn't >>> work >>> here. Making it non-local just means that we would need to know the >>> static >>> call graph, which we don't because we haven't devirtualized yet so all >>> the >>> calls are indirect. >>> Nick >> >> So that means you're now saying that llvm.invariant.end ought to be >> left the way it is, right? > > I have no idea how to make use of llvm.invariant to help devirtualization. > If...

...a and successfully reconstruct the class > hierarchy. Can anyone help with this? > > We're also open to alternative approaches, but we'd like to stay in LLVM > IR as much as possible. Implement field-sensitive interprocedural sparse conditional constant propagation and it will devirtualize. The reason I don't like having an explicit devirtualization pass is that it requires a large amount of analysis (interprocedural, no less!) and is strictly single-purpose. The way that LLVM does devirtualization now is through a series of tons of tiny steps: * the very last stage in dev...

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, though I did not dig deeper as I'm not sure if this kind of behavior is expected at current stage of New PM life or not? If it is not expected then I'ld be happy to file a bug and...

...;t >>>> know that they won't modify the vptr in advance, so invariant doesn't >>>> work >>>> here. Making it non-local just means that we would need to know the >>>> static >>>> call graph, which we don't because we haven't devirtualized yet so all >>>> the >>>> calls are indirect. >>>> Nick >>> >>> So that means you're now saying that llvm.invariant.end ought to be >>> left the way it is, right? >> >> I have no idea how to make use of llvm.invariant to...

...ew 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 indirect calls is not enough since inlining can produce indirect calls (which could then get devirtualized by later passes). One (ugly) fix is to pass the value handles to the inliner through CGSCCUpdateResult and let the inliner augment it as t...

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

...;t >>>> know that they won't modify the vptr in advance, so invariant doesn't >>>> work >>>> here. Making it non-local just means that we would need to know the >>>> static >>>> call graph, which we don't because we haven't devirtualized yet so all >>>> the >>>> calls are indirect. >>>> Nick >>> >>> So that means you're now saying that llvm.invariant.end ought to be >>> left the way it is, right? >> >> I have no idea how to make use of llvm.invariant...

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

...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 that we would need to know the static >> call graph, which we don't because we haven't devirtualized yet so all the >> calls are indirect. >> Nick > > So that means you're now saying that llvm.invariant.end ought to be > left the way it is, right? I have no idea how to make use of llvm.invariant to help devirtualization. If no use or other use case for them can be found...

...gt; know that they won't modify the vptr in advance, so invariant doesn't >>>>> work >>>>> here. Making it non-local just means that we would need to know the >>>>> static >>>>> call graph, which we don't because we haven't devirtualized yet so all >>>>> the >>>>> calls are indirect. >>>>> Nick >>>> >>>> So that means you're now saying that llvm.invariant.end ought to be >>>> left the way it is, right? >>> >>> I have no idea how...

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

...ess 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 that we would need to know the static > call graph, which we don't because we haven't devirtualized yet so all the > calls are indirect. > Nick So that means you're now saying that llvm.invariant.end ought to be left the way it is, right? I've been thinking about how to better take the invariant regions into account, and it quickly became clear that it would be easier to handle i...

...nd then calls a virtual > function on the instance, then the virtual function being called and > the constructor will have been maximally simplified (F refs the > constructor, and the constructor refs all the virtual functions), and > you're more likely to inline the constructor and devirtualize the > call. I don't have any real data to back up that this will materially > help, though. Sanjoy, this is a good example. The code pattern is basically like this: Worker(Base *B) { B->vCall(); } Factory::create(Kind K) { if (K == ..) return new D1(); else ... } Calle...

...ntptr %class.TestVirtual* %pinstance, i64 0, i32 0 ; Populate the instance's vtbl pointer. After this, the instance is constructed. store %classvtbltype.TestVirtual* @classvtbl.TestVirtual, %classvtbltype.TestVirtual** %ppVtbl ; If this next call is commented out, the virtual method call is devirtualized by -std-compile-opts %puts = call i32 @puts(i8* getelementptr inbounds ([2 x i8]* @str, i32 0, i32 0)) ; Call the virtual function. ; load the instance's vtbl pointer. %pVtbl1 = load %classvtbltype.TestVirtual** %ppVtbl ; load the function pointer from the vtbl %ppVfn1 = getelementptr %cla...

...ey won't modify the vptr in advance, so invariant doesn't >>>>>> work >>>>>> here. Making it non-local just means that we would need to know the >>>>>> static >>>>>> call graph, which we don't because we haven't devirtualized yet so all >>>>>> the >>>>>> calls are indirect. >>>>>> Nick >>>>> >>>>> So that means you're now saying that llvm.invariant.end ought to be >>>>> left the way it is, right? >>>> &g...