https://gcc.gnu.org/g:4ee692337c4ec18fe9be3df34f3607ea3de5ef93
commit r15-3631-g4ee692337c4ec18fe9be3df34f3607ea3de5ef93
Author: Jason Merrill <ja...@redhat.com>
Date: Thu Sep 12 16:22:02 2024 -0400
c++: -fimplicit-constexpr diagnostic improvement [PR116696]
PR116696 expressed surprise that explicit 'constexpr' was needed on one
function; this was because the function isn't 'inline', and
-fimplicit-constexpr doesn't try to promote non-inline functions. Let's be
more helpful in that situation, and also help trace through functions that
were promoted.
PR c++/116696
gcc/cp/ChangeLog:
* constexpr.cc (explain_invalid_constexpr_fn): When
-fimplicit-constexpr, also explain inline functions, and point out
non-inline functions.
gcc/testsuite/ChangeLog:
* g++.dg/DRs/dr2478.C: Prune extra diagnostic.
* g++.dg/ext/fimplicit-constexpr1.C: New test.
Diff:
---
gcc/cp/constexpr.cc | 7 +++++++
gcc/testsuite/g++.dg/DRs/dr2478.C | 2 +-
gcc/testsuite/g++.dg/ext/fimplicit-constexpr1.C | 8 ++++++++
3 files changed, 16 insertions(+), 1 deletion(-)
diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index db2a9c1543e1..d0f617481413 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -1057,9 +1057,16 @@ explain_invalid_constexpr_fn (tree fun)
/* Only diagnose defaulted functions, lambdas, or instantiations. */
else if (!DECL_DEFAULTED_FN (fun)
&& !LAMBDA_TYPE_P (CP_DECL_CONTEXT (fun))
+ && !(flag_implicit_constexpr
+ && !DECL_DECLARED_CONSTEXPR_P (fun)
+ && DECL_DECLARED_INLINE_P (fun))
&& !is_instantiation_of_constexpr (fun))
{
inform (DECL_SOURCE_LOCATION (fun), "%qD declared here", fun);
+ if (flag_implicit_constexpr && !maybe_constexpr_fn (fun)
+ && decl_defined_p (fun))
+ inform (DECL_SOURCE_LOCATION (fun),
+ "%<-fimplicit-constexpr%> only affects %<inline%> functions");
return;
}
if (diagnosed == NULL)
diff --git a/gcc/testsuite/g++.dg/DRs/dr2478.C
b/gcc/testsuite/g++.dg/DRs/dr2478.C
index 7f581cabb7b0..b2292561381a 100644
--- a/gcc/testsuite/g++.dg/DRs/dr2478.C
+++ b/gcc/testsuite/g++.dg/DRs/dr2478.C
@@ -2,7 +2,7 @@
// { dg-do compile { target c++20 } }
// Defeat -fimplicit-constexpr
-int ii;
+int ii; // { dg-prune-output "value of 'ii' is not usable in a constant expr" }
template <typename T>
struct S {
diff --git a/gcc/testsuite/g++.dg/ext/fimplicit-constexpr1.C
b/gcc/testsuite/g++.dg/ext/fimplicit-constexpr1.C
new file mode 100644
index 000000000000..fc4b2829b657
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/fimplicit-constexpr1.C
@@ -0,0 +1,8 @@
+// { dg-additional-options -fimplicit-constexpr }
+// { dg-do compile { target c++14 } }
+
+void f() { } // { dg-message "'-fimplicit-constexpr' only affects 'inline'
functions" }
+
+inline int g() { f(); return 42; } // { dg-error {non-'constexpr' function
'void f\(\)'} }
+
+constexpr int i = g(); // { dg-error {'int g\(\)' called in a constant
expression} }
