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* [gcc r14-9950] c++: ICE with temporary of class type in array DMI [PR109966]
@ 2024-04-12 22:26 Marek Polacek
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From: Marek Polacek @ 2024-04-12 22:26 UTC (permalink / raw)
To: gcc-cvs
https://gcc.gnu.org/g:6039925631780741ba77666ef2ef743aa2a925a8
commit r14-9950-g6039925631780741ba77666ef2ef743aa2a925a8
Author: Marek Polacek <polacek@redhat.com>
Date: Mon Mar 11 17:45:55 2024 -0400
c++: ICE with temporary of class type in array DMI [PR109966]
This ICE started with the fairly complicated r13-765. We crash in
gimplify_var_or_parm_decl because a stray VAR_DECL leaked there.
The problem is ultimately that potential_prvalue_result_of wasn't
correctly handling arrays and replace_placeholders_for_class_temp_r
replaced a PLACEHOLDER_EXPR in a TARGET_EXPR which is used in the
context of copy elision. If I have
M m[2] = { M{""}, M{""} };
then we don't invoke the M(const M&) copy-ctor.
One part of the fix is to use TARGET_EXPR_ELIDING_P rather than
potential_prvalue_result_of. That unfortunately doesn't handle the
case like
struct N { N(M); };
N arr[2] = { M{""}, M{""} };
because TARGET_EXPRs that initialize a function argument are not
marked TARGET_EXPR_ELIDING_P even though gimplify_arg drops such
TARGET_EXPRs on the floor. We can use a pset to avoid replacing
placeholders in them.
I made an attempt to use set_target_expr_eliding in
convert_for_arg_passing but that regressed constexpr-diag1.C, and does
not seem like a prudent change in stage 4 anyway.
PR c++/109966
gcc/cp/ChangeLog:
* typeck2.cc (potential_prvalue_result_of): Remove.
(replace_placeholders_for_class_temp_r): Check TARGET_EXPR_ELIDING_P.
Use a pset. Don't replace_placeholders in TARGET_EXPRs that initialize
a function argument.
gcc/testsuite/ChangeLog:
* g++.dg/cpp1y/nsdmi-aggr20.C: New test.
* g++.dg/cpp1y/nsdmi-aggr21.C: New test.
Diff:
---
gcc/cp/typeck2.cc | 55 +++++++++-------------------
gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr20.C | 17 +++++++++
gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr21.C | 59 +++++++++++++++++++++++++++++++
3 files changed, 92 insertions(+), 39 deletions(-)
diff --git a/gcc/cp/typeck2.cc b/gcc/cp/typeck2.cc
index 31198b2f9f5..2985bfdf9ec 100644
--- a/gcc/cp/typeck2.cc
+++ b/gcc/cp/typeck2.cc
@@ -1399,41 +1399,6 @@ digest_init_flags (tree type, tree init, int flags, tsubst_flags_t complain)
return digest_init_r (type, init, 0, flags, complain);
}
-/* Return true if SUBOB initializes the same object as FULL_EXPR.
- For instance:
-
- A a = A{}; // initializer
- A a = (A{}); // initializer
- A a = (1, A{}); // initializer
- A a = true ? A{} : A{}; // initializer
- auto x = A{}.x; // temporary materialization
- auto x = foo(A{}); // temporary materialization
-
- FULL_EXPR is the whole expression, SUBOB is its TARGET_EXPR subobject. */
-
-static bool
-potential_prvalue_result_of (tree subob, tree full_expr)
-{
- if (subob == full_expr)
- return true;
- else if (TREE_CODE (full_expr) == TARGET_EXPR)
- {
- tree init = TARGET_EXPR_INITIAL (full_expr);
- if (TREE_CODE (init) == COND_EXPR)
- return (potential_prvalue_result_of (subob, TREE_OPERAND (init, 1))
- || potential_prvalue_result_of (subob, TREE_OPERAND (init, 2)));
- else if (TREE_CODE (init) == COMPOUND_EXPR)
- return potential_prvalue_result_of (subob, TREE_OPERAND (init, 1));
- /* ??? I don't know if this can be hit. */
- else if (TREE_CODE (init) == PAREN_EXPR)
- {
- gcc_checking_assert (false);
- return potential_prvalue_result_of (subob, TREE_OPERAND (init, 0));
- }
- }
- return false;
-}
-
/* Callback to replace PLACEHOLDER_EXPRs in a TARGET_EXPR (which isn't used
in the context of guaranteed copy elision). */
@@ -1441,11 +1406,13 @@ static tree
replace_placeholders_for_class_temp_r (tree *tp, int *, void *data)
{
tree t = *tp;
- tree full_expr = *static_cast<tree *>(data);
+ auto pset = static_cast<hash_set<tree> *>(data);
/* We're looking for a TARGET_EXPR nested in the whole expression. */
if (TREE_CODE (t) == TARGET_EXPR
- && !potential_prvalue_result_of (t, full_expr))
+ /* That serves as temporary materialization, not an initializer. */
+ && !TARGET_EXPR_ELIDING_P (t)
+ && !pset->add (t))
{
tree init = TARGET_EXPR_INITIAL (t);
while (TREE_CODE (init) == COMPOUND_EXPR)
@@ -1460,6 +1427,16 @@ replace_placeholders_for_class_temp_r (tree *tp, int *, void *data)
gcc_checking_assert (!find_placeholders (init));
}
}
+ /* TARGET_EXPRs initializing function arguments are not marked as eliding,
+ even though gimplify_arg drops them on the floor. Don't go replacing
+ placeholders in them. */
+ else if (TREE_CODE (t) == CALL_EXPR || TREE_CODE (t) == AGGR_INIT_EXPR)
+ for (int i = 0; i < call_expr_nargs (t); ++i)
+ {
+ tree arg = get_nth_callarg (t, i);
+ if (TREE_CODE (arg) == TARGET_EXPR && !TARGET_EXPR_ELIDING_P (arg))
+ pset->add (arg);
+ }
return NULL_TREE;
}
@@ -1507,8 +1484,8 @@ digest_nsdmi_init (tree decl, tree init, tsubst_flags_t complain)
temporary materialization does not occur when initializing an object
from a prvalue of the same type, therefore we must not replace the
placeholder with a temporary object so that it can be elided. */
- cp_walk_tree (&init, replace_placeholders_for_class_temp_r, &init,
- nullptr);
+ hash_set<tree> pset;
+ cp_walk_tree (&init, replace_placeholders_for_class_temp_r, &pset, nullptr);
return init;
}
diff --git a/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr20.C b/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr20.C
new file mode 100644
index 00000000000..4796d861e83
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr20.C
@@ -0,0 +1,17 @@
+// PR c++/109966
+// { dg-do compile { target c++14 } }
+
+#define SA(X) static_assert ((X),#X)
+
+struct A {
+ int a;
+ int b = a;
+};
+
+struct B {
+ int x = 0;
+ int y[1]{A{x}.b};
+};
+
+constexpr B b = { };
+SA(b.y[0] == 0);
diff --git a/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr21.C b/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr21.C
new file mode 100644
index 00000000000..efec45bc1a8
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr21.C
@@ -0,0 +1,59 @@
+// PR c++/109966
+// { dg-do compile { target c++14 } }
+
+struct k {
+ k(const char *);
+};
+struct M {
+ k name;
+ int j = 42;
+ int i = j;
+};
+
+M m = M{""};
+
+struct S {
+ M arr1[1]{M{""}};
+ M a1[1] = { (M{""}) };
+ M a2[1] = { (true, M{""}) };
+ M a3[1] = { true ? M{""} : M{""} };
+ M arr2[2]{M{""}, M{""}};
+ M arr3[3]{M{""}, M{""}, M{""}};
+
+ M arr1e[1] = {M{""}};
+ M arr2e[2] = {M{""}, M{""}};
+ M arr3e[3] = {M{""}, M{""}, M{""}};
+
+ M arr1l[1] = { m };
+ M arr2l[2] = { m, m };
+ M arr3l[3] = { m, m, m };
+
+ M m1 = M{""};
+ M m2 = m;
+ M m3{M{""}};
+ M m4 = {M{""}};
+} o;
+
+struct N {
+ N(M);
+};
+
+struct Z {
+ N arr1[1]{ M{""} };
+ N arr2[2]{ M{""}, M{""} };
+ N arr1e[1] = { M{""} };
+ N arr2e[2] = { M{""}, M{""} };
+} z;
+
+struct Y {
+ k name;
+ int j = 42;
+ int i = j;
+ operator M();
+};
+
+struct W {
+ M arr1[1]{ Y{""} };
+ M arr2[2]{ Y{""}, Y{""} };
+ M arr3[3]{ Y{""}, Y{""}, Y{""} };
+} w;
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