nickdesaulniers added inline comments.
================ Comment at: clang/lib/CodeGen/CGExprConstant.cpp:1131-1132 + case CK_NullToPointer: { + if (llvm::Constant *C = Visit(subExpr, destType)) + if (C->isNullValue()) + return CGM.EmitNullConstant(destType); ---------------- efriedma wrote: > nickdesaulniers wrote: > > FWIW, I would have thought these might be unnecessary, but we do trip 2 > > tests without these guards IIRC. > The fact that the Visit can fail doesn't surprise me; you can write arbitrary > expressions of type nullptr_t (for example, `nullptr_t f(); void* g = f();`. > I can't think of any reason you'd need to check C->isNullValue(), though; do > you have a testcase for that? Failed Tests (2): Clang :: CodeGenCXX/const-init-cxx11.cpp Clang :: CodeGenCXX/cxx11-thread-local-instantiated.cpp Looking at the first: ``` decltype(nullptr) null(); int *p = null(); ``` and the corresponding AST: ``` |-FunctionDecl 0x5650ebbb44a8 <x.cpp:2:3, col:26> col:21 used null 'decltype(nullptr) ()' `-VarDecl 0x5650ebbb45e0 <line:3:3, col:17> col:8 p 'int *' cinit `-ImplicitCastExpr 0x5650ebbb4740 <col:12, col:17> 'int *' <NullToPointer> `-CallExpr 0x5650ebbb4720 <col:12, col:17> 'decltype(nullptr)':'std::nullptr_t' `-ImplicitCastExpr 0x5650ebbb4708 <col:12> 'decltype(nullptr) (*)()' <FunctionToPointerDecay> `-DeclRefExpr 0x5650ebbb4690 <col:12> 'decltype(nullptr) ()' lvalue Function 0x5650ebbb44a8 'null' 'decltype(nullptr) ()' ``` we change the existing test case from having a `__cxx_global_var_init` routine, i.e.: ``` @p = dso_local global ptr null, align 8 @llvm.global_ctors = appending global [1 x { i32, ptr, ptr }] [{ i32, ptr, ptr } { i32 65535, ptr @_GLOBAL__sub_I_x.cpp, ptr null }] ; Function Attrs: noinline uwtable define internal void @__cxx_global_var_init() #0 section ".text.startup" { entry: %call = call ptr @_Z4nullv() store ptr null, ptr @p, align 8 ret void } declare ptr @_Z4nullv() #1 ; Function Attrs: noinline uwtable define internal void @_GLOBAL__sub_I_x.cpp() #0 section ".text.startup" { entry: call void @__cxx_global_var_init() ret void } ``` to simply: ``` @p = dso_local global ptr null, align 8 ``` So it seems nice to skip having the static constructors, but then `@_Z4nullv` is never invoked. That seems problematic? (I expect the fast path to fail once it recurses down to the DeclRefExpr, but that requires the subexpr of the ImplicitCastExpr be visited). --- So I think the code as written is good to go. WDYT? Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D156175/new/ https://reviews.llvm.org/D156175 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits