[PATCH] c++: ICE w/ maybe_warn_nodiscard on non-dep call [PR123495, PR126860]

Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK
for trunk? It's a checking-only ICE so no big need to backport,
maybe to 16 at most.

-- >8 --

Another latent issue uncovered by the NON_DEPENDENT_EXPR removal.
cp_get_fndecl_from_callee, called from maybe_warn_nodiscard, tries to
fold the templated callee via constant evaluation, but constant
evaluation expects non-templated trees.  So use fold_non_dependent_expr
which instantiates templated trees beforehand.

	PR c++/123495
	PR c++/126860

gcc/cp/ChangeLog:

	* cvt.cc (cp_get_fndecl_from_callee): Use fold_non_dependent_expr
	instead of maybe_constant_init.

gcc/testsuite/ChangeLog:

	* g++.dg/template/non-dependent36.C: New test.
	* g++.dg/template/non-dependent37.C: New test.
---
 gcc/cp/cvt.cc                                   | 2 +-
 gcc/testsuite/g++.dg/template/non-dependent36.C | 4 ++++
 gcc/testsuite/g++.dg/template/non-dependent37.C | 9 +++++++++
 3 files changed, 14 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/template/non-dependent36.C
 create mode 100644 gcc/testsuite/g++.dg/template/non-dependent37.C

diff --git a/gcc/cp/cvt.cc b/gcc/cp/cvt.cc
index a378b51a2bed..33d528b3c324 100644
--- a/gcc/cp/cvt.cc
+++ b/gcc/cp/cvt.cc
@@ -1069,7 +1069,7 @@ cp_get_fndecl_from_callee (tree fn, bool fold /* = true */)
   if (type == NULL_TREE || !INDIRECT_TYPE_P (type))
     return NULL_TREE;
   if (fold)
-    fn = maybe_constant_init (fn);
+    fn = fold_non_dependent_expr (fn);
   STRIP_NOPS (fn);
   if (TREE_CODE (fn) == ADDR_EXPR
       || TREE_CODE (fn) == FDESC_EXPR)
diff --git a/gcc/testsuite/g++.dg/template/non-dependent36.C b/gcc/testsuite/g++.dg/template/non-dependent36.C
new file mode 100644
index 000000000000..a4bf06974028
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/non-dependent36.C
@@ -0,0 +1,4 @@
+// PR c++/123495
+
+template <int N>
+void foo () { ((int (*) ()) 0) (); }
diff --git a/gcc/testsuite/g++.dg/template/non-dependent37.C b/gcc/testsuite/g++.dg/template/non-dependent37.C
new file mode 100644
index 000000000000..ad58cf6f10ce
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/non-dependent37.C
@@ -0,0 +1,9 @@
+// PR c++/126860
+
+struct A {
+  int (*foo)();
+};
+
+template <typename T> struct S : public A {
+  void bar() { A::foo(); }
+};
-- 
2.55.0.559.g11c6700f10