[llvm-dev] False Negatives Wunused-function in clang found by gcc

[David Blaikie via llvm-dev]

Any reason it shouldn't be a subgroup of -Wunused-function? I guess maybe
because people already had codebases that were -Wunused-function clean, and
we wouldn't want to regress that/start warning on new things/force them to
have to add -Wno-unused-member-function to unbreak their builds?

(I guess there's some history here? Like perhaps -Wunused-function was
initially implemented without member function support, and it was added
later & so added under a separate flag to make rollout easier? But I think
it'd probably still be OK for it to be under a subgroup - people could opt
out of it initially without losing all their existing
-Wunused-function-cleanliness, and opt in if they ever decided to do the
extra cleanup)

On Tue, Mar 2, 2021 at 6:05 AM Aaron Ballman <aaron at aaronballman.com> wrote:

> On Mon, Mar 1, 2021 at 8:22 PM David Blaikie <dblaikie at gmail.com> wrote:
> >
> > Not sure where the regression might've leaked in. But does seem to be
> something to do with anonymous namespace support and member functions:
> https://godbolt.org/z/zz8WP1
>
> I don't think there's a regression here, unless I'm missing something.
> -Wunused-member-function is what diagnoses this
> (https://godbolt.org/z/MxP4h6) but it is not a subgroup of either
> -Wunused-function or -Wunused
> (
> https://github.com/llvm/llvm-project/blob/main/clang/include/clang/Basic/DiagnosticGroups.td#L839
> ).
> Perhaps we should explicitly enable it?
>
> ~Aaron
>
> >
> >
> >
> > On Mon, Mar 1, 2021 at 5:12 PM Luke Benes via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
> >>
> >>
> >> By building llvm-project with gcc 7 and 10, I found multiple
> Wunused-function warnings that clang 11/12 missed.
> >>
> >> All of these warnings were recently introduced, and the authors fixed
> many of them.   Any ideas why clang misses so many of this category? And
> why the ones missed are recent changes to the llvm codebase?
> >>
> >> -Luke
> >>
> >>
> >> ==========
> >>
> >>  After dab953c8e44a2 with gcc 10.2.1, I see the following new warnings:
> >>
> >> [ 65%] Building CXX object
> lib/Linker/CMakeFiles/LLVMLinker.dir/IRMover.cpp.o
> >> /llvm/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp:1600:1:
> warning: ‘std::pair<llvm::Value*, llvm::Value*>
> {anonymous}::DataFlowSanitizer::getShadowOriginAddress(llvm::Value*,
> llvm::Align, llvm::Instruction*)’ defined but not used [-Wunused-function]
> >>  1600 | DataFlowSanitizer::getShadowOriginAddress(Value *Addr, Align
> InstAlignment,
> >>       | ^~~~~~~~~~~~~~~~~
> >> /llvm/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp:1510:6:
> warning: ‘void {anonymous}::DFSanFunction::setOrigin(llvm::Instruction*,
> llvm::Value*)’ defined but not used [-Wunused-function]
> >>  1510 | void DFSanFunction::setOrigin(Instruction *I, Value *Origin) {
> >>       |      ^~~~~~~~~~~~~
> >> /llvm/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp:1476:8:
> warning: ‘llvm::Value* {anonymous}::DFSanFunction::getOrigin(llvm::Value*)’
> defined but not used [-Wunused-function]
> >>  1476 | Value *DFSanFunction::getOrigin(Value *V) {
> >>       |        ^~~~~~~~~~~~~
> >> /llvm/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp:1469:8:
> warning: ‘llvm::Value* {anonymous}::DFSanFunction::getRetvalOriginTLS()’
> defined but not used [-Wunused-function]
> >>  1469 | Value *DFSanFunction::getRetvalOriginTLS() { return
> DFS.RetvalOriginTLS; }
> >>       |        ^~~~~~~~~~~~~
> >>
> >> FIX:
> https://github.com/llvm/llvm-project/commit/9524632fa2bf8c894e4aac27f03631a1915d84d3
> >>
> >> ==========
> >>
> >> After bc8e262afe83, with gcc 10.1 but not clang 11, I'm seeing:
> >>
> >> [ 21%] Building CXX object
> lib/MC/MCParser/CMakeFiles/LLVMMCParser.dir/MasmParser.cpp.o
> >> /llvm/lib/MC/MCParser/MasmParser.cpp:3836:6: warning: ‘bool
> {anonymous}::MasmParser::emitStructValue(const {anonymous}::StructInfo&)’
> defined but not used [-Wunused-function]
> >>  3836 | bool MasmParser::emitStructValue(const StructInfo &Structure) {
> >>       |      ^~~~~~~~~~
> >>
> >> FIX: https://reviews.llvm.org/D83898
> >>
> >> ==========
> >>
> >> In 931a68f26b9a3, I'm seeing the following warning with gcc7 and gcc10:
> >> [ 70%] Building CXX object
> lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/RegAllocPBQP.cpp.o
> >> /llvm/lib/CodeGen/RegAllocFast.cpp:384:6: warning: ‘bool
> {anonymous}::RegAllocFast::verifyRegStateMapping(const
> {anonymous}::RegAllocFast::LiveReg&) const’ defined but not used
> [-Wunused-function]
> >>  bool RegAllocFast::verifyRegStateMapping(const LiveReg &LR) const {
> >>       ^~~~~~~~~~~~
> >>
> >> FIX: 0671a4c5087d40450603d9d26cf239f1a8b1367e
> >>
> >> _______________________________________________
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> >> llvm-dev at lists.llvm.org
> >> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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