https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122185
--- Comment #27 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jakub Jelinek <[email protected]>: https://gcc.gnu.org/g:fb22d7f3b665555cfb55673ca2b954f860d28b50 commit r16-5506-gfb22d7f3b665555cfb55673ca2b954f860d28b50 Author: Jakub Jelinek <[email protected]> Date: Sat Nov 22 12:24:35 2025 +0100 c++: Readd type checks for cp_fold -ffold-simple-inlines foldings [PR122185] In GCC15, cp_fold -ffold-simple-inlines code contained if (INDIRECT_TYPE_P (TREE_TYPE (x)) && INDIRECT_TYPE_P (TREE_TYPE (r))) check around the optimization, but as std::to_underlying has been added to the set, it got removed. Now, the check isn't needed when using correct libstdc++-v3 headers, because the function template types ensure the converted types are sane (so for most of them both are some kind of REFERENCE_TYPEs, for addressof one REFERENCE_TYPE and one POINTER_TYPE, for to_underlying one ENUMERAL_TYPE and one INTEGRAL_TYPE_P). But when some fuzzer or user attempts to implement one or more of those std:: functions and does it wrong (sure, such code is invalid), we can ICE because build_nop certainly doesn't handle all possible type conversions. So, the following patch readds the INDIRECT_REF_P && INDIRECT_REF_P check for everything but to_underlying, for which it checks ENUMERAL_TYPE to INTEGRAL_TYPE_P. That way we don't ICE on bogus code. Though, I wonder about 2 things, whether the CALL_EXPR_ARG in there shouldn't be also guarded just in case somebody tries to compile namespace std { int to_underlying (); }; int a = std::to_underlying (); and also whether this to_underlying folding doesn't behave differently from the libstdc++-v3 implementation if the enum is enum A : bool { B, C }; I think -fno-fold-simple-inlines will compile it as != 0, while the -ffold-simple-inlines code just as a cast. Sure, enum with underlying bool can't contain enumerators with values other than 0 and 1, but it is still 8-bit at least and so what happens with other values? 2025-11-22 Jakub Jelinek <[email protected]> PR c++/122185 * cp-gimplify.cc (cp_fold) <case CALL_EXPR>: For -ffold-simple-inlines restore check that both types are INDIRECT_TYPE_P, except for "to_underlying" check that r has ENUMERAL_TYPE and x has INTEGRAL_TYPE_P. * g++.dg/cpp1z/pr122185.C: New test.
