From 0a0c2c3f06227d46b5e9542dfdd4e0fd2d67d894 Mon Sep 17 00:00:00 2001 From: Jakub Jelinek Date: Fri, 18 Mar 2022 18:49:23 +0100 Subject: [PATCH] c++: Fix up constexpr evaluation of new with zero sized types [PR104568] The new expression constant expression evaluation right now tries to deduce how many elts the array it uses for the heap or heap [] vars should have (or how many elts should its trailing array have if it has cookie at the start). As new is lowered at that point to (some_type *) ::operator new (size) or so, it computes it by subtracting cookie size if any from size, then divides the result by sizeof (some_type). This works fine for most types, except when sizeof (some_type) is 0, then we divide by zero; size is then equal to cookie_size (or if there is no cookie, to 0). The following patch special cases those cases so that we don't divide by zero and also recover the original outer_nelts from the expression by forcing the size not to be folded in that case but be explicit 0 * outer_nelts or cookie_size + 0 * outer_nelts. Note, we have further issues, we accept-invalid various cases, for both zero sized elt_type and even non-zero sized elts, we aren't able to diagnose out of bounds POINTER_PLUS_EXPR like: constexpr bool foo () { auto p = new int[2]; auto q1 = &p[0]; auto q2 = &p[1]; auto q3 = &p[2]; auto q4 = &p[3]; delete[] p; return true; } constexpr bool a = foo (); That doesn't look like a regression so I think we should resolve that for GCC 13, but there are 2 problems. Figure out why cxx_fold_pointer_plus_expression doesn't deal with the &heap [] etc. cases, and for the zero sized arrays, I think we really need to preserve whether user wrote an array ref or pointer addition, because in the &p[3] case if sizeof(p[0]) == 0 we know that if it has 2 elements it is out of bounds, while if we see p p+ 0 the information if it was p + 2 or p + 3 in the source is lost. clang++ seems to handle it fine even in the zero sized cases or with new expressions. 2022-03-18 Jakub Jelinek PR c++/104568 * init.cc (build_new_constexpr_heap_type): Remove FULL_SIZE argument and its handling, instead add ITYPE2 argument. Only support COOKIE_SIZE != NULL. (build_new_1): If size is 0, change it to 0 * outer_nelts if outer_nelts is non-NULL. Pass type rather than elt_type to maybe_wrap_new_for_constexpr. * constexpr.cc (build_new_constexpr_heap_type): New function. (cxx_eval_constant_expression) : If elt_size is zero sized type, try to recover outer_nelts from the size argument to operator new/new[] and pass that as arg_size to build_new_constexpr_heap_type. Pass ctx, non_constant_p and overflow_p to that call too. * g++.dg/cpp2a/constexpr-new22.C: New test. --- gcc/cp/constexpr.cc | 95 +++++++++++++++++++++++++++- gcc/cp/init.cc | 38 ++++------- gcc/testsuite/g++.dg/cpp2a/constexpr-new22.C | 42 ++++++++++++ 3 files changed, 149 insertions(+), 26 deletions(-) create mode 100644 gcc/testsuite/g++.dg/cpp2a/constexpr-new22.C diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc index bbb6cd9..a3136ce 100644 --- a/gcc/cp/constexpr.cc +++ b/gcc/cp/constexpr.cc @@ -6422,6 +6422,84 @@ maybe_warn_about_constant_value (location_t loc, tree decl) } } +/* For element type ELT_TYPE, return the appropriate type of the heap object + containing such element(s). COOKIE_SIZE is NULL or the size of cookie + in bytes. If COOKIE_SIZE is NULL, return array type + ELT_TYPE[FULL_SIZE / sizeof(ELT_TYPE)], otherwise return + struct { size_t[COOKIE_SIZE/sizeof(size_t)]; ELT_TYPE[N]; } + where N is is computed such that the size of the struct fits into FULL_SIZE. + If ARG_SIZE is non-NULL, it is the first argument to the new operator. + It should be passed if ELT_TYPE is zero sized type in which case FULL_SIZE + will be also 0 and so it is not possible to determine the actual array + size. CTX, NON_CONSTANT_P and OVERFLOW_P are used during constant + expression evaluation of subexpressions of ARG_SIZE. */ + +static tree +build_new_constexpr_heap_type (const constexpr_ctx *ctx, tree elt_type, + tree cookie_size, tree full_size, tree arg_size, + bool *non_constant_p, bool *overflow_p) +{ + gcc_assert (cookie_size == NULL_TREE || tree_fits_uhwi_p (cookie_size)); + gcc_assert (tree_fits_uhwi_p (full_size)); + unsigned HOST_WIDE_INT csz = cookie_size ? tree_to_uhwi (cookie_size) : 0; + if (arg_size) + { + STRIP_NOPS (arg_size); + if (cookie_size) + { + if (TREE_CODE (arg_size) != PLUS_EXPR) + arg_size = NULL_TREE; + else if (TREE_CODE (TREE_OPERAND (arg_size, 0)) == INTEGER_CST + && tree_int_cst_equal (cookie_size, + TREE_OPERAND (arg_size, 0))) + { + arg_size = TREE_OPERAND (arg_size, 1); + STRIP_NOPS (arg_size); + } + else if (TREE_CODE (TREE_OPERAND (arg_size, 1)) == INTEGER_CST + && tree_int_cst_equal (cookie_size, + TREE_OPERAND (arg_size, 1))) + { + arg_size = TREE_OPERAND (arg_size, 0); + STRIP_NOPS (arg_size); + } + else + arg_size = NULL_TREE; + } + if (arg_size && TREE_CODE (arg_size) == MULT_EXPR) + { + tree op0 = TREE_OPERAND (arg_size, 0); + tree op1 = TREE_OPERAND (arg_size, 1); + if (integer_zerop (op0)) + arg_size + = cxx_eval_constant_expression (ctx, op1, false, non_constant_p, + overflow_p); + else if (integer_zerop (op1)) + arg_size + = cxx_eval_constant_expression (ctx, op0, false, non_constant_p, + overflow_p); + else + arg_size = NULL_TREE; + } + else + arg_size = NULL_TREE; + } + + unsigned HOST_WIDE_INT fsz = tree_to_uhwi (arg_size ? arg_size : full_size); + if (!arg_size) + { + unsigned HOST_WIDE_INT esz = int_size_in_bytes (elt_type); + gcc_assert (fsz >= csz); + fsz -= csz; + if (esz) + fsz /= esz; + } + tree itype2 = build_index_type (size_int (fsz - 1)); + if (!cookie_size) + return build_cplus_array_type (elt_type, itype2); + return build_new_constexpr_heap_type (elt_type, cookie_size, itype2); +} + /* Attempt to reduce the expression T to a constant value. On failure, issue diagnostic and return error_mark_node. */ /* FIXME unify with c_fully_fold */ @@ -7253,6 +7331,7 @@ cxx_eval_constant_expression (const constexpr_ctx *ctx, tree t, tree var_size = TYPE_SIZE_UNIT (TREE_TYPE (var)); tree elt_type = TREE_TYPE (type); tree cookie_size = NULL_TREE; + tree arg_size = NULL_TREE; if (TREE_CODE (elt_type) == RECORD_TYPE && TYPE_NAME (elt_type) == heap_identifier) { @@ -7264,9 +7343,21 @@ cxx_eval_constant_expression (const constexpr_ctx *ctx, tree t, 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))) + arg_size = CALL_EXPR_ARG (oldop, 0); TREE_TYPE (var) - = build_new_constexpr_heap_type (elt_type, cookie_size, - var_size); + = build_new_constexpr_heap_type (ctx, elt_type, cookie_size, + var_size, arg_size, + non_constant_p, overflow_p); TREE_TYPE (TREE_OPERAND (op, 0)) = build_pointer_type (TREE_TYPE (var)); } diff --git a/gcc/cp/init.cc b/gcc/cp/init.cc index cd1d6f8..7575597 100644 --- a/gcc/cp/init.cc +++ b/gcc/cp/init.cc @@ -2931,33 +2931,17 @@ std_placement_new_fn_p (tree alloc_fn) } /* For element type ELT_TYPE, return the appropriate type of the heap object - containing such element(s). COOKIE_SIZE is NULL or the size of cookie - in bytes. FULL_SIZE is NULL if it is unknown how big the heap allocation - will be, otherwise size of the heap object. If COOKIE_SIZE is NULL, - return array type ELT_TYPE[FULL_SIZE / sizeof(ELT_TYPE)], otherwise return + containing such element(s). COOKIE_SIZE is the size of cookie in bytes. + Return struct { size_t[COOKIE_SIZE/sizeof(size_t)]; ELT_TYPE[N]; } - where N is nothing (flexible array member) if FULL_SIZE is NULL, otherwise - it is computed such that the size of the struct fits into FULL_SIZE. */ + where N is nothing (flexible array member) if ITYPE2 is NULL, otherwise + the array has ITYPE2 as its TYPE_DOMAIN. */ tree -build_new_constexpr_heap_type (tree elt_type, tree cookie_size, tree full_size) +build_new_constexpr_heap_type (tree elt_type, tree cookie_size, tree itype2) { - gcc_assert (cookie_size == NULL_TREE || tree_fits_uhwi_p (cookie_size)); - gcc_assert (full_size == NULL_TREE || tree_fits_uhwi_p (full_size)); - unsigned HOST_WIDE_INT csz = cookie_size ? tree_to_uhwi (cookie_size) : 0; - tree itype2 = NULL_TREE; - if (full_size) - { - unsigned HOST_WIDE_INT fsz = tree_to_uhwi (full_size); - gcc_assert (fsz >= csz); - fsz -= csz; - fsz /= int_size_in_bytes (elt_type); - itype2 = build_index_type (size_int (fsz - 1)); - if (!cookie_size) - return build_cplus_array_type (elt_type, itype2); - } - else - gcc_assert (cookie_size); + gcc_assert (tree_fits_uhwi_p (cookie_size)); + unsigned HOST_WIDE_INT csz = tree_to_uhwi (cookie_size); csz /= int_size_in_bytes (sizetype); tree itype1 = build_index_type (size_int (csz - 1)); tree atype1 = build_cplus_array_type (sizetype, itype1); @@ -3408,6 +3392,12 @@ build_new_1 (vec **placement, tree type, tree nelts, outer_nelts_check = NULL_TREE; } + /* If size is zero e.g. due to type having zero size, try to + preserve outer_nelts for constant expression evaluation + purposes. */ + if (integer_zerop (size) && outer_nelts) + size = build2 (MULT_EXPR, TREE_TYPE (size), size, outer_nelts); + alloc_call = build_operator_new_call (fnname, placement, &size, &cookie_size, align_arg, outer_nelts_check, @@ -3484,7 +3474,7 @@ build_new_1 (vec **placement, tree type, tree nelts, } if (cookie_size) - alloc_call = maybe_wrap_new_for_constexpr (alloc_call, elt_type, + alloc_call = maybe_wrap_new_for_constexpr (alloc_call, type, cookie_size); /* In the simple case, we can stop now. */ diff --git a/gcc/testsuite/g++.dg/cpp2a/constexpr-new22.C b/gcc/testsuite/g++.dg/cpp2a/constexpr-new22.C new file mode 100644 index 0000000..9af9c9f --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp2a/constexpr-new22.C @@ -0,0 +1,42 @@ +// PR c++/104568 +// { dg-do compile { target c++20 } } +// { dg-options "" } + +struct S { int s; constexpr S () : s (0) {} constexpr ~S () {} }; +typedef int T[0]; +typedef int U[0]; + +constexpr bool +foo () +{ + auto p = new T[2]; + auto q1 = &p[0]; + auto q2 = &p[1]; + auto q3 = &p[2]; + delete[] p; + return true; +} + +constexpr bool +bar () +{ + auto p = new U[2]; + auto q1 = &p[0]; + auto q2 = &p[1]; + auto q3 = &p[2]; + delete[] p; + return true; +} + +constexpr bool +baz () +{ + auto p = new T[0]; + auto q1 = &p[0]; + delete[] p; + return true; +} + +constexpr bool a = foo (); +constexpr bool b = bar (); +constexpr bool c = baz (); -- 2.7.4