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* [gcc r12-5252] c++: constexpr virtual and vbase thunk
@ 2021-11-15 7:47 Jason Merrill
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From: Jason Merrill @ 2021-11-15 7:47 UTC (permalink / raw)
To: gcc-cvs
https://gcc.gnu.org/g:267318a2857a42922c3ca033dac4690172b17683
commit r12-5252-g267318a2857a42922c3ca033dac4690172b17683
Author: Jason Merrill <jason@redhat.com>
Date: Wed Nov 10 16:42:04 2021 -0500
c++: constexpr virtual and vbase thunk
C++20 allows virtual functions to be constexpr. I don't think that calling
through a pointer to a vbase subobject is supposed to work in a constant
expression, since an object with virtual bases can't be constant, but the
call shouldn't ICE.
gcc/cp/ChangeLog:
* constexpr.c (cxx_eval_thunk_call): Error instead of ICE
on vbase thunk to constexpr function.
gcc/testsuite/ChangeLog:
* g++.dg/cpp2a/constexpr-virtual20.C: New test.
Diff:
---
gcc/cp/constexpr.c | 15 ++++++++++-----
gcc/testsuite/g++.dg/cpp2a/constexpr-virtual20.C | 22 ++++++++++++++++++++++
2 files changed, 32 insertions(+), 5 deletions(-)
diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index 453007c686b..7c27131f506 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -2246,15 +2246,20 @@ cxx_eval_thunk_call (const constexpr_ctx *ctx, tree t, tree thunk_fndecl,
{
tree function = THUNK_TARGET (thunk_fndecl);
- /* virtual_offset is only set in the presence of virtual bases, which make
- the class non-literal, so we don't need to handle it here. */
if (THUNK_VIRTUAL_OFFSET (thunk_fndecl))
{
- gcc_assert (!DECL_DECLARED_CONSTEXPR_P (function));
if (!ctx->quiet)
{
- error ("call to non-%<constexpr%> function %qD", function);
- explain_invalid_constexpr_fn (function);
+ if (!DECL_DECLARED_CONSTEXPR_P (function))
+ {
+ error ("call to non-%<constexpr%> function %qD", function);
+ explain_invalid_constexpr_fn (function);
+ }
+ else
+ /* virtual_offset is only set for virtual bases, which make the
+ class non-literal, so we don't need to handle it here. */
+ error ("calling constexpr member function %qD through virtual "
+ "base subobject", function);
}
*non_constant_p = true;
return t;
diff --git a/gcc/testsuite/g++.dg/cpp2a/constexpr-virtual20.C b/gcc/testsuite/g++.dg/cpp2a/constexpr-virtual20.C
new file mode 100644
index 00000000000..3c411fa3fcc
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/constexpr-virtual20.C
@@ -0,0 +1,22 @@
+// Test for constexpr call through vbase thunk.
+// { dg-do compile { target c++20 } }
+
+class Rep {
+public:
+ constexpr virtual int foo() { return 1; }
+};
+
+class VBase {
+public:
+ constexpr virtual int foo() { return 2; }
+};
+
+class Main : public Rep, virtual public VBase {
+public:
+ constexpr virtual int foo() { return 5; }
+};
+
+int main() {
+ Main m;
+ static_assert(static_cast<VBase*>(&m)->foo() == 5); // { dg-error "" }
+}
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