On Fri, Mar 11, 2022 at 11:28:09PM -0500, Jason Merrill wrote: > > @@ -7264,9 +7265,66 @@ cxx_eval_constant_expression (const cons > > DECL_NAME (var) > > = (DECL_NAME (var) == heap_uninit_identifier > > ? heap_identifier : heap_vec_identifier); > > + /* For zero sized elt_type, try to recover how many outer_nelts > > + it should have. */ > > + if ((cookie_size ? tree_int_cst_equal (var_size, cookie_size) > > + : integer_zerop (var_size)) > > + && !int_size_in_bytes (elt_type) > > + && TREE_CODE (oldop) == CALL_EXPR > > + && call_expr_nargs (oldop) >= 1) > > + if (tree fun = get_function_named_in_call (oldop)) > > + if (cxx_replaceable_global_alloc_fn (fun) > > + && IDENTIFIER_NEW_OP_P (DECL_NAME (fun))) > > + { > > + tree arg0 = CALL_EXPR_ARG (oldop, 0); > > How about setting var_size to arg0 at this point, and moving the > decomposition of the size expression into build_new_constexpr_heap_type?
That would be more difficult, because for the cxx_eval_constant_expression calls we need ctx, non_constant_p and overflow_p arguments, so build_new_constexpr_heap_type would need to remove that one bool arg added by this patch but instead pass around those 3 new ones. As build_new_constexpr_heap_type is called only from 2 spots where the other one passes NULL as full_size, the decomposition is only useful for this caller and not the other one. But if you strongly prefer it that way, I can do that. Note, probably not 3 new args but 4, depends on whether we could turn all those cases where the tree arg0 = CALL_EXPR_ARG (oldop, 0); is done but var_size_adjusted is false into assertion failures. I'm worried that with the zero size of element we could end up with a variable number of elements which when multiplied by 0 gives constant 0, though hopefully that would be rejected earlier during constant evaluation. > > > + STRIP_NOPS (arg0); > > + if (cookie_size) > > + { > > + if (TREE_CODE (arg0) != PLUS_EXPR) > > + arg0 = NULL_TREE; > > + else if (TREE_CODE (TREE_OPERAND (arg0, 0)) > > + == INTEGER_CST > > + && tree_int_cst_equal (cookie_size, > > + TREE_OPERAND (arg0, > > + 0))) > > + { > > + arg0 = TREE_OPERAND (arg0, 1); > > + STRIP_NOPS (arg0); > > + } > > + else if (TREE_CODE (TREE_OPERAND (arg0, 1)) > > + == INTEGER_CST > > + && tree_int_cst_equal (cookie_size, > > + TREE_OPERAND (arg0, > > + 1))) > > + { > > + arg0 = TREE_OPERAND (arg0, 0); > > + STRIP_NOPS (arg0); > > + } > > + else > > + arg0 = NULL_TREE; > > + } > > + if (arg0 && TREE_CODE (arg0) == MULT_EXPR) > > + { > > + tree op0 = TREE_OPERAND (arg0, 0); > > + tree op1 = TREE_OPERAND (arg0, 1); > > + var_size_adjusted = true; > > + if (integer_zerop (op0)) > > + var_size > > + = cxx_eval_constant_expression (ctx, op1, false, > > + non_constant_p, > > + overflow_p); > > + else if (integer_zerop (op1)) > > + var_size > > + = cxx_eval_constant_expression (ctx, op0, false, > > + non_constant_p, > > + overflow_p); > > + else > > + var_size_adjusted = false; > > + } > > + } > > TREE_TYPE (var) > > = build_new_constexpr_heap_type (elt_type, cookie_size, > > - var_size); > > + var_size, var_size_adjusted); > > TREE_TYPE (TREE_OPERAND (op, 0)) > > = build_pointer_type (TREE_TYPE (var)); > > } Jakub