[C++ PATCH] PR c++/93324 - ICE with -Wall on constexpr if.

[Marek Polacek]

This is a crash with constexpr if, when trying to see if the call in
the if-statement is std::is_constant_evaluated.

cp_get_callee_fndecl_nofold can return NULL_TREE and fndecl_built_in_p
doesn't expect to get a null tree, so check FNDECL first.

Bootstrapped/regtested on x86_64-linux, ok for trunk?

        * semantics.c (is_std_constant_evaluated_p): Check fndecl.

        * g++.dg/cpp1z/constexpr-if33.C: New test.
---
 gcc/cp/semantics.c                          |  4 ++--
 gcc/testsuite/g++.dg/cpp1z/constexpr-if33.C | 16 ++++++++++++++++
 2 files changed, 18 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp1z/constexpr-if33.C

diff --git a/gcc/cp/semantics.c b/gcc/cp/semantics.c
index 3669b247e34..9051a2863e0 100644
--- a/gcc/cp/semantics.c
+++ b/gcc/cp/semantics.c
@@ -734,8 +734,8 @@ is_std_constant_evaluated_p (tree fn)
     return false;
 
   tree fndecl = cp_get_callee_fndecl_nofold (fn);
-  if (fndecl_built_in_p (fndecl, CP_BUILT_IN_IS_CONSTANT_EVALUATED,
-                        BUILT_IN_FRONTEND))
+  if (fndecl && fndecl_built_in_p (fndecl, CP_BUILT_IN_IS_CONSTANT_EVALUATED,
+                                  BUILT_IN_FRONTEND))
     return true;
 
   if (!decl_in_std_namespace_p (fndecl))
diff --git a/gcc/testsuite/g++.dg/cpp1z/constexpr-if33.C 
b/gcc/testsuite/g++.dg/cpp1z/constexpr-if33.C
new file mode 100644
index 00000000000..e5ef659932b
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/constexpr-if33.C
@@ -0,0 +1,16 @@
+// PR c++/93324 - ICE with -Wall on constexpr if.
+// { dg-do compile { target c++17 } }
+// { dg-options "-Wall" }
+
+struct {
+  template <int>
+  static constexpr bool a() { return 0; }
+} e;
+
+template <typename>
+void d()
+{
+  auto c(e);
+  using b = decltype(c);
+  if constexpr (b::a<2>());
+}

base-commit: bcfc2227c556f2801a657ce3007374732baa8333
-- 
2.24.1