Implement LLVM IR Virtual Function Elimination for Swift classes. #39128
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lib/IRGen/GenMeta.cpp
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| var->addTypeMetadata(offset, typeIdForMethod(*this, method)); | ||
| } | ||
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| switch (getOptions().VCallVisibility) { |
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Why not deriving the VCall visibility from the method visibility?
Setting the visibility for all calls sounds dangerous, e.g. if a public method gets a "File" visibility.
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That's right, it is dangerous -- incorrectly set visibility will cause miscompiles. I've added this to be used in tests, where I need to make sure the method isn't going to eliminated by the SIL optimizer, so it's public, but I want the LLVM IR optimizer to eliminate it, therefore the vcall visibility set to "file".
Open to any better suggestions?
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You can call a private/internal method from a function, annotated with @_optimize(none). That will keep the virtual call alive
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Changed the PR to infer the vtable visibility from the class decl's access scope visibility.
lib/IRGen/GenMeta.cpp
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| @@ -334,6 +334,33 @@ void IRGenModule::emitNonoverriddenMethodDescriptor(const SILVTable *VTable, | |||
| getAddrOfLLVMVariable(entity, init, DebugTypeInfo()); | |||
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| void IRGenModule::addVTableTypeMetadata(llvm::GlobalVariable *var, | |||
| SmallVector<std::pair<Size, SILDeclRef>, 8> vtableEntries) { | |||
| if (!getOptions().VirtualFunctionElimination) | |||
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This is already checked at the call site
kubamracek
changed the title
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LGTM.
It would be good if @aschwaighofer takes a look, too.
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@swift-ci please test |
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@swift-ci please test |
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@swift-ci please test |
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@swift-ci please test |
- Virtual calls are done via a @llvm.type.checked.load instrinsic call with a type identifier - Type identifier of a vfunc is the base method's mangling - Type descriptors and class metadata get !type markers that list offsets and type identifiers of all vfuncs - The -enable-llvm-vfe frontend flag enables VFE - Two added tests verify the behavior on IR and by executing a program
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@swift-ci please test |
Depends on changes in LLVM (some unmerged yet): https://reviews.llvm.org/D107645, https://reviews.llvm.org/D108741, https://reviews.llvm.org/D109114, https://reviews.llvm.org/D109169.