From: Jonathan Wakely <jwakely@redhat.com>
Date: Wed, 3 May 2023 20:40:01 +0000 (+0100)
Subject: libstdc++: Ensure constexpr std::lcm detects out-of-range result [PR105844]
X-Git-Tag: releases/gcc-10.5.0~103
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=b357af31b8d1e93f0f70133e25d3ad4045f7a32b;p=thirdparty%2Fgcc.git

libstdc++: Ensure constexpr std::lcm detects out-of-range result [PR105844]

On the gcc-10 branch, __glibcxx_assert does not unconditionally check
the condition during constant evaluation. This means we need an explicit
additional check for std::lcm results that cannot be represented in an
unsigned result type.

libstdc++-v3/ChangeLog:

	PR libstdc++/105844
	* include/std/numeric (lcm): Ensure out-of-range result is
	detected in constant evaluation.
	* testsuite/26_numerics/lcm/105844.cc: Adjust dg-error string.
---

diff --git a/libstdc++-v3/include/std/numeric b/libstdc++-v3/include/std/numeric
index b81b5e4a30f4..f4636679223d 100644
--- a/libstdc++-v3/include/std/numeric
+++ b/libstdc++-v3/include/std/numeric
@@ -161,6 +161,11 @@ namespace __detail
 #endif
 
       bool __overflow = __builtin_mul_overflow(__r, __n2, &__r);
+#if defined _GLIBCXX_HAVE_BUILTIN_IS_CONSTANT_EVALUATED
+      if (__builtin_is_constant_evaluated())
+	if (__overflow)
+	  _GLIBCXX_THROW_OR_ABORT("std::lcm result is out of range of type");
+#endif
       __glibcxx_assert(!__overflow);
       return __r;
     }
diff --git a/libstdc++-v3/testsuite/26_numerics/lcm/105844.cc b/libstdc++-v3/testsuite/26_numerics/lcm/105844.cc
index 0b5ef5ae5e90..c7338f3cbf39 100644
--- a/libstdc++-v3/testsuite/26_numerics/lcm/105844.cc
+++ b/libstdc++-v3/testsuite/26_numerics/lcm/105844.cc
@@ -19,6 +19,6 @@ constexpr int d = std::lcm(49999, 50000); // { dg-error "overflow" }
 // Similarly for unsigned, but the diagnostic is a failed assertion instead.
 constexpr int e = std::lcm(500000u, 499999); // { dg-error "in 'constexpr'" }
 constexpr int f = std::lcm(499999u, 500000); // { dg-error "in 'constexpr'" }
-// { dg-error "unreachable" "" { target *-*-* } 0 }
+// { dg-error "throw.* not a constant expression" "" { target *-*-* } 0 }
 
 // { dg-prune-output "in 'constexpr' expansion" }