[PATCH] c++: ICE with constexpr lambda [PR107280]

[Marek Polacek <polacek@redhat.com>]

We crash here since r10-3661, the store_init_value hunk in particular.
Before, we called cp_fully_fold_init, so e.g.

  {.str=VIEW_CONVERT_EXPR<char[8]>("")}

was folded into

  {.str=""}

but now we don't fold and keep the VCE around, and it causes trouble in
cxx_eval_store_expression: in the !refs->is_empty () loop we descend on
.str's initializer but since it's wrapped in a VCE, we skip the STRING_CST
check and then crash on the CONSTRUCTOR_NO_CLEARING.

Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk/12?

	PR c++/107280

gcc/cp/ChangeLog:

	* constexpr.cc (cxx_eval_store_expression): Strip location wrappers.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp1z/constexpr-lambda28.C: New test.
---
 gcc/cp/constexpr.cc                             |  3 ++-
 gcc/testsuite/g++.dg/cpp1z/constexpr-lambda28.C | 15 +++++++++++++++
 2 files changed, 17 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp1z/constexpr-lambda28.C

diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index 8683c00596a..abf6ee560c5 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -6033,7 +6033,8 @@ cxx_eval_store_expression (const constexpr_ctx *ctx, tree t,
 	  *valp = build_constructor (type, NULL);
 	  CONSTRUCTOR_NO_CLEARING (*valp) = no_zero_init;
 	}
-      else if (TREE_CODE (*valp) == STRING_CST)
+      else if (STRIP_ANY_LOCATION_WRAPPER (*valp),
+	       TREE_CODE (*valp) == STRING_CST)
 	{
 	  /* An array was initialized with a string constant, and now
 	     we're writing into one of its elements.  Explode the
diff --git a/gcc/testsuite/g++.dg/cpp1z/constexpr-lambda28.C b/gcc/testsuite/g++.dg/cpp1z/constexpr-lambda28.C
new file mode 100644
index 00000000000..aafbfddd8b9
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/constexpr-lambda28.C
@@ -0,0 +1,15 @@
+// PR c++/107280
+// { dg-do compile { target c++17 } }
+
+struct string {
+  char str[8] = "";
+};
+template <int, int> constexpr void
+test ()
+{
+  string str{};
+  auto append = [&](const char *s) { *str.str = *s; };
+  append("");
+}
+
+static_assert ((test<true, true>(), true), "");

base-commit: 2b2340e236c0bba8aaca358ea25a5accd8249fbd
-- 
2.39.2