[COMMITTED] c++: Unshare expressions from constexpr cache.

[Jason Merrill]

Another place we need to unshare cached expressions.

Tested x86_64-pc-linux-gnu, applying to trunk.

        PR c++/92852 - ICE with generic lambda and reference var.
        * constexpr.c (maybe_constant_value): Likewise.
---
 gcc/cp/constexpr.c                               |  2 +-
 gcc/testsuite/g++.dg/cpp1y/lambda-generic-ref1.C | 12 ++++++++++++
 gcc/testsuite/g++.dg/cpp1z/decomp48.C            |  8 ++++----
 3 files changed, 17 insertions(+), 5 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp1y/lambda-generic-ref1.C

diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index f6b8f331bc9..8e8806345c1 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -6598,7 +6598,7 @@ maybe_constant_value (tree t, tree decl, bool 
manifestly_const_eval)
   if (cv_cache == NULL)
     cv_cache = hash_map<tree, tree>::create_ggc (101);
   if (tree *cached = cv_cache->get (t))
-    return *cached;
+    return unshare_expr_without_location (*cached);
 
   r = cxx_eval_outermost_constant_expr (t, true, true, false, false, decl);
   gcc_checking_assert (r == t
diff --git a/gcc/testsuite/g++.dg/cpp1y/lambda-generic-ref1.C 
b/gcc/testsuite/g++.dg/cpp1y/lambda-generic-ref1.C
new file mode 100644
index 00000000000..a96fa1ce237
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/lambda-generic-ref1.C
@@ -0,0 +1,12 @@
+// PR c++/92852
+// { dg-do compile { target c++14 } }
+
+struct S { int operator<<(const int &); } glob;
+void foo()
+{
+  S& message_stream = glob;
+  auto format = [&message_stream](auto && x)
+               { message_stream << x ; };
+  format(3);
+  format(4u);
+}
diff --git a/gcc/testsuite/g++.dg/cpp1z/decomp48.C 
b/gcc/testsuite/g++.dg/cpp1z/decomp48.C
index 3c50b02a6c2..35413c79a9d 100644
--- a/gcc/testsuite/g++.dg/cpp1z/decomp48.C
+++ b/gcc/testsuite/g++.dg/cpp1z/decomp48.C
@@ -18,7 +18,7 @@ f2 ()
 {
   S v {1, 2};
   auto& [s, t] = v;    // { dg-warning "structured bindings only available 
with" "" { target c++14_down } }
-  return s;            // { dg-warning "reference to local variable 'v' 
returned" "" { target *-*-* } .-1 }
+  return s;            // { dg-warning "reference to local variable 'v' 
returned" }
 }
 
 int &
@@ -33,7 +33,7 @@ f4 ()
 {
   int a[3] = {1, 2, 3};
   auto& [s, t, u] = a; // { dg-warning "structured bindings only available 
with" "" { target c++14_down } }
-  return s;            // { dg-warning "reference to local variable 'a' 
returned" "" { target *-*-* } .-1 }
+  return s;            // { dg-warning "reference to local variable 'a' 
returned" }
 }
 
 int &
@@ -78,7 +78,7 @@ f10 ()
 {
   S v {1, 2};
   auto& [s, t] = v;    // { dg-warning "structured bindings only available 
with" "" { target c++14_down } }
-  return &s;           // { dg-warning "address of local variable 'v' 
returned" "" { target *-*-* } .-1 }
+  return &s;           // { dg-warning "address of local variable 'v' 
returned" }
 }
 
 int *
@@ -93,7 +93,7 @@ f12 ()
 {
   int a[3] = {1, 2, 3};
   auto& [s, t, u] = a; // { dg-warning "structured bindings only available 
with" "" { target c++14_down } }
-  return &s;           // { dg-warning "address of local variable 'a' 
returned" "" { target *-*-* } .-1 }
+  return &s;           // { dg-warning "address of local variable 'a' 
returned" }
 }
 
 int *

base-commit: 64c9f2d9972ad359a32f0a97ee0a806c2532db15
-- 
2.18.1