Tested x86_64-pc-linux-gnu, applying to trunk.
-- 8< --
Here, when dealing with a class with a complex subobject structure, we would
try and fail to find the relevant FIELD_DECL for an empty base before giving
up. And we would do this at each level, in a combinatorially problematic
way. Instead, we should check for an empty base first.
PR c++/109678
gcc/cp/ChangeLog:
* constexpr.cc (cxx_fold_indirect_ref_1): Handle empty base first.
gcc/testsuite/ChangeLog:
* g++.dg/cpp1z/variant1.C: New test.
---
gcc/cp/constexpr.cc | 23 +++++++------
gcc/testsuite/g++.dg/cpp1z/variant1.C | 47 +++++++++++++++++++++++++++
2 files changed, 60 insertions(+), 10 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp1z/variant1.C
diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index d1097764b10..37d1c444c9e 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -5446,6 +5446,19 @@ cxx_fold_indirect_ref_1 (const constexpr_ctx *ctx,
location_t loc, tree type,
return ret;
}
}
+
+ /* Handle conversion to an empty base class, which is represented with a
+ NOP_EXPR. Do this before spelunking into the non-empty subobjects,
+ which is likely to be a waste of time (109678). */
+ if (is_empty_class (type)
+ && CLASS_TYPE_P (optype)
+ && DERIVED_FROM_P (type, optype))
+ {
+ if (empty_base)
+ *empty_base = true;
+ return op;
+ }
+
for (tree field = TYPE_FIELDS (optype);
field; field = DECL_CHAIN (field))
if (TREE_CODE (field) == FIELD_DECL
@@ -5468,16 +5481,6 @@ cxx_fold_indirect_ref_1 (const constexpr_ctx *ctx,
location_t loc, tree type,
return ret;
}
}
- /* Also handle conversion to an empty base class, which
- is represented with a NOP_EXPR. */
- if (is_empty_class (type)
- && CLASS_TYPE_P (optype)
- && DERIVED_FROM_P (type, optype))
- {
- if (empty_base)
- *empty_base = true;
- return op;
- }
}
return NULL_TREE;
diff --git a/gcc/testsuite/g++.dg/cpp1z/variant1.C
b/gcc/testsuite/g++.dg/cpp1z/variant1.C
new file mode 100644
index 00000000000..9b18cc233ca
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/variant1.C
@@ -0,0 +1,47 @@
+// PR c++/109678
+// With the bug, compiling this testcase takes more than the typical timeout.
+// { dg-do compile { target c++17 } }
+
+#include <variant>
+
+struct A {};
+struct B {};
+struct C {};
+struct D {};
+struct E {};
+struct F {};
+struct G {};
+struct H {};
+struct I {};
+struct J {};
+struct K {};
+struct L {};
+struct M {};
+struct N {};
+struct O {};
+struct P {};
+struct Q {};
+struct R {};
+struct S {};
+struct T {};
+struct U {};
+struct V {};
+struct W {
+ // gcc13 + compiler explorer = 20000ms
+ // gcc12.2 + compiler explorer = 400ms
+ int i;
+};
+struct X {};
+struct Y {};
+struct Z {};
+
+using Foo = std::variant<A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R,
S, T, U, V, W, X, Y, Z>;
+
+struct Bar {
+ Foo f;
+ static Bar dummy() {
+ // issue is triggered by this initialization
+ return {Z{}};
+ // return {A{}}; // would be very quick
+ }
+};
base-commit: bc24c51c0ccd64617864897ad071c98004ffc0a4
--
2.31.1
