From 5c64df80df274c753bfc8415bd902e1180e76f6a Mon Sep 17 00:00:00 2001
From: Jakub Jelinek <jakub@redhat.com>
Date: Mon, 10 Aug 2020 17:53:46 +0200
Subject: [PATCH] c++: Fix constexpr evaluation of SPACESHIP_EXPR [PR96497]
The following valid testcase is rejected, because cxx_eval_binary_expression
is called on the SPACESHIP_EXPR with lval = true, as the address of the
spaceship needs to be passed to a method call.
After recursing on the operands and calling genericize_spaceship which turns
it into a TARGET_EXPR with initialization, we call cxx_eval_constant_expression
on it which succeeds, but then we fall through into code that will
VERIFY_CONSTANT (r) which FAILs because it is an address of a variable. Rather
than avoiding that for lval = true and SPACESHIP_EXPR, the patch just tail
calls cxx_eval_constant_expression - I believe that call should perform all
the needed verifications.
2020-08-10 Jakub Jelinek <jakub@redhat.com>
PR c++/96497
* constexpr.c (cxx_eval_binary_expression): For SPACESHIP_EXPR, tail
call cxx_eval_constant_expression after genericize_spaceship to avoid
undesirable further VERIFY_CONSTANT.
* g++.dg/cpp2a/spaceship-constexpr3.C: New test.
---
gcc/cp/constexpr.c | 4 ++--
gcc/testsuite/g++.dg/cpp2a/spaceship-constexpr3.C | 7 +++++++
2 files changed, 9 insertions(+), 2 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/spaceship-constexpr3.C
diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index ab747a58fa0a..8ee0f2abe1ad 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -3085,8 +3085,8 @@ cxx_eval_binary_expression (const constexpr_ctx *ctx, tree t,
else if (code == SPACESHIP_EXPR)
{
r = genericize_spaceship (type, lhs, rhs);
- r = cxx_eval_constant_expression (ctx, r, lval, non_constant_p,
- overflow_p);
+ return cxx_eval_constant_expression (ctx, r, lval, non_constant_p,
+ overflow_p);
}
if (r == NULL_TREE)
diff --git a/gcc/testsuite/g++.dg/cpp2a/spaceship-constexpr3.C b/gcc/testsuite/g++.dg/cpp2a/spaceship-constexpr3.C
new file mode 100644
index 000000000000..95f03e6e231f
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/spaceship-constexpr3.C
@@ -0,0 +1,7 @@
+// PR c++/96497
+// { dg-do compile { target c++20 } }
+
+#include <compare>
+
+static_assert(std::partial_ordering(std::strong_ordering::less) < 0);
+static_assert(std::partial_ordering(1 <=> 2) < 0);
--
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