https://gcc.gnu.org/g:cffe5fd7c98babd85acf86f3e7f8d02b04416ec2
commit r16-7182-gcffe5fd7c98babd85acf86f3e7f8d02b04416ec2 Author: Jakub Jelinek <[email protected]> Date: Fri Jan 30 11:40:17 2026 +0100 fold-const: Fix implicit cast to nullptr_t typedef [PR123790] The following testcase is incorrectly rejected, because since r15-6744 it adds build_nop to preserve the exact typedef type and cxx_eval_constant_expression can't fold NOP_EXPR from integer_zerop of one NULLPTR_TYPE to another NULLPTR_TYPE, while cxx_eval_constant_expression relies on fold to do such folding. I see 3 options to fix that, one is deal with this in the r15-6744 spot and special case NULLPTR_TYPE there and build_zero_cst instead of build_nop (with similar condition like in the patch below), another possibility is special case this in cxx_eval_constant_expression, and another one (done in this patch) is to handle this in fold-const.cc - fold_convert_loc and also in fold_convert_const. 2026-01-30 Jakub Jelinek <[email protected]> PR c++/123790 * fold-const.cc (fold_convert_const): Handle conversion of integer_zerop to NULLPTR_TYPE. (fold_convert_loc): Likewise. * g++.dg/cpp0x/nullptr47.C: New test. Diff: --- gcc/fold-const.cc | 6 ++++++ gcc/testsuite/g++.dg/cpp0x/nullptr47.C | 10 ++++++++++ 2 files changed, 16 insertions(+) diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc index 47cd0053d31a..82d8ef5092e8 100644 --- a/gcc/fold-const.cc +++ b/gcc/fold-const.cc @@ -2566,6 +2566,8 @@ fold_convert_const (enum tree_code code, tree type, tree arg1) return v.build (); } } + else if (TREE_CODE (type) == NULLPTR_TYPE && integer_zerop (arg1)) + return build_zero_cst (type); return NULL_TREE; } @@ -2788,6 +2790,10 @@ fold_convert_loc (location_t loc, tree type, tree arg) tem = fold_ignored_result (arg); return fold_build1_loc (loc, NOP_EXPR, type, tem); + case NULLPTR_TYPE: + if (integer_zerop (arg)) + return build_zero_cst (type); + /* FALLTHRU */ default: if (TYPE_MAIN_VARIANT (type) == TYPE_MAIN_VARIANT (orig)) return fold_build1_loc (loc, NOP_EXPR, type, arg); diff --git a/gcc/testsuite/g++.dg/cpp0x/nullptr47.C b/gcc/testsuite/g++.dg/cpp0x/nullptr47.C new file mode 100644 index 000000000000..4c4071b65248 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp0x/nullptr47.C @@ -0,0 +1,10 @@ +// PR c++/123790 +// { dg-do compile { target c++11 } } + +int +main () +{ + using nullptr_t = decltype (nullptr); + constexpr nullptr_t zero = nullptr; + constexpr nullptr_t other_zero = zero; +}
