In gcc-11, -Wnonnull considers the implicit this argument of every C++ nonstatic member function to have been implicitly declared with attribute nonnull and triggers warnings for calls where the pointer is null. [1] Should clang also do this? This change helped webkit identify and fix some issues. [2][3][4][5] Building clang trunk with gcc-11 produces 13 new warnings related to this enhancement. They are in MachineModuleInfo.cpp and RangeAdapterTest.cpp.[6] Do these look like valid issues? -Luke [1] https://gcc.gnu.org/gcc-11/changes.html\ [2] https://bugs.webkit.org/show_bug.cgi?id=224838 [3] https://bugs.webkit.org/show_bug.cgi?id=224826 [4] https://trac.webkit.org/changeset/276343/webkit [5] https://bugs.webkit.org/show_bug.cgi?id=224452 [6] https://pastebin.com/EJTZphGm
Sure, those things seem legit - I think we have some sanitizer mode (& some optimizations, when the sanitizer checks aren't enabled) for checking non-null-ness in various cases, which probably would hit these cases (though given that I think various sanitizer self host builds are checked regularly, I wonder if there's an interesting explanation for why the cases in [6] were not found already by runtime analysis like that) - probably makes sense to catch them at compile time where we can. Though clang's warnings aren't interprocedural like it looks like some of these warnings in [6] are, so clang might still not catch all of them. On Wed, Sep 1, 2021 at 11:44 AM Luke Benes via llvm-dev < llvm-dev at lists.llvm.org> wrote:> > > In gcc-11, -Wnonnull considers the implicit this argument of every C++ > nonstatic member function to have been implicitly declared with attribute > nonnull and triggers warnings for calls where the pointer is null. [1] > > Should clang also do this? This change helped webkit identify and fix some > issues. [2][3][4][5] > > Building clang trunk with gcc-11 produces 13 new warnings related to this > enhancement. They are in MachineModuleInfo.cpp and RangeAdapterTest.cpp.[6] > Do these look like valid issues? > > -Luke > > > [1] https://gcc.gnu.org/gcc-11/changes.html\ > [2] https://bugs.webkit.org/show_bug.cgi?id=224838 > [3] https://bugs.webkit.org/show_bug.cgi?id=224826 > [4] https://trac.webkit.org/changeset/276343/webkit > [5] https://bugs.webkit.org/show_bug.cgi?id=224452 > [6] https://pastebin.com/EJTZphGm > > > _______________________________________________ > LLVM Developers mailing list > llvm-dev at lists.llvm.org > https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev >-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20210901/7419b605/attachment.html>
James Y Knight via llvm-dev
2021-Sep-01 19:57 UTC
[llvm-dev] Change in -Wnonnull in gcc-11
The first warning looks valid, although it doesn't happen at runtime.
1. In constructor ‘llvm::MachineModuleInfo::MachineModuleInfo(const
llvm::LLVMTargetMachine*)’,
2. inlined from
‘llvm::MachineModuleInfoWrapperPass::MachineModuleInfoWrapperPass(const
llvm::LLVMTargetMachine*)’ at
/llvm/lib/CodeGen/MachineModuleInfo.cpp:357:26,
3. inlined from ‘llvm::Pass* llvm::callDefaultCtor() [with PassName
llvm::MachineModuleInfoWrapperPass]’ at
/llvm/include/llvm/PassSupport.h:80:76:
4. /llvm/lib/CodeGen/MachineModuleInfo.cpp:240:51: warning: ‘this’
pointer is null [-Wnonnull]
5. 240 | Context.setObjectFileInfo(TM->getObjFileLowering());
6.
I believe it should be a simple matter of deleting the zero-arg
constructor. I'll try that and push it.
I note that the GCC warning points to an odd place, though -- it probably
should be pointing to the construction TM(*TM), which initializes a
reference with null, which is already UB.
MachineModuleInfo::MachineModuleInfo(const LLVMTargetMachine *TM)
: TM(*TM), ....
However, the rest of the warnings come from:
decltype(static_cast<const TypeParam
*>(nullptr)->rbegin())>::value
which I think is a false-positive in GCC's warning.
TTBOMK, calling a method on nullptr in an unevaluated context (e.g.
decltype, non-vla-sizeof, etc) is not UB, and therefore should not emit a
warning.
On Wed, Sep 1, 2021, 2:44 PM Luke Benes via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
>
>
> In gcc-11, -Wnonnull considers the implicit this argument of every C++
> nonstatic member function to have been implicitly declared with attribute
> nonnull and triggers warnings for calls where the pointer is null. [1]
>
> Should clang also do this? This change helped webkit identify and fix some
> issues. [2][3][4][5]
>
> Building clang trunk with gcc-11 produces 13 new warnings related to this
> enhancement. They are in MachineModuleInfo.cpp and RangeAdapterTest.cpp.[6]
> Do these look like valid issues?
>
> -Luke
>
>
> [1] https://gcc.gnu.org/gcc-11/changes.html\
> [2] https://bugs.webkit.org/show_bug.cgi?id=224838
> [3] https://bugs.webkit.org/show_bug.cgi?id=224826
> [4] https://trac.webkit.org/changeset/276343/webkit
> [5] https://bugs.webkit.org/show_bug.cgi?id=224452
> [6] https://pastebin.com/EJTZphGm
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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