On 3/16/22 12:55, Jakub Jelinek wrote:
On Tue, Mar 15, 2022 at 04:19:05PM -0400, Jason Merrill wrote:
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.
Or we could move all the adjustment into a separate function and only ever
pass the number of elements to build_new_constexpr_heap_type?
So like this?
2022-03-16 Jakub Jelinek <ja...@redhat.com>
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) <case CONVERT_EXPR>:
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.jj 2022-03-16 15:25:26.294551244 +0100
+++ gcc/cp/constexpr.cc 2022-03-16 17:27:08.202184961 +0100
@@ -6422,6 +6422,84 @@ maybe_warn_about_constant_value (locatio
}
}
+/* 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. */
+
+tree
Let's make this static.
+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);
+ unsigned HOST_WIDE_INT esz = int_size_in_bytes (elt_type);
esz could move inside the if.
OK with those changes, thanks.
+ if (!arg_size)
+ {
+ 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 cons
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 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)))
+ 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));
}
--- gcc/cp/init.cc.jj 2022-03-16 15:25:26.431549398 +0100
+++ gcc/cp/init.cc 2022-03-16 17:23:03.922500101 +0100
@@ -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<tree, va_gc> **placemen
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<tree, va_gc> **placemen
}
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. */
--- gcc/testsuite/g++.dg/cpp2a/constexpr-new22.C.jj 2022-03-16
16:45:04.011372629 +0100
+++ gcc/testsuite/g++.dg/cpp2a/constexpr-new22.C 2022-03-16
16:45:04.011372629 +0100
@@ -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 ();
Jakub
