[pushed] c++: Fix DMI with lambda 'this' capture [PR94205]

[Jason Merrill <jason@redhat.com>]

We represent 'this' in a default member initializer with a PLACEHOLDER_EXPR.
Normally in constexpr evaluation when we encounter one it refers to
ctx->ctor, but when we're creating a temporary of class type, that replaces
ctx->ctor, so a PLACEHOLDER_EXPR that refers to the type of the member being
initialized needs to be replaced before that happens.

This patch fixes the testcase below, but not the original testcase from the PR,
which is still broken due to PR94219.

Tested x86_64-pc-linux-gnu, applying to trunk and 9.

gcc/cp/ChangeLog
2020-03-31  Jason Merrill  <jason@redhat.com>

	PR c++/94205
	* constexpr.c (cxx_eval_constant_expression) [TARGET_EXPR]: Call
	replace_placeholders.
	* typeck2.c (store_init_value): Fix arguments to
	fold_non_dependent_expr.
---
 gcc/cp/constexpr.c                            |  6 ++++++
 gcc/cp/tree.c                                 |  2 +-
 gcc/cp/typeck2.c                              |  2 +-
 gcc/testsuite/g++.dg/cpp0x/constexpr-nsdmi2.C | 20 +++++++++++++++++++
 gcc/testsuite/g++.dg/cpp1z/lambda-this4.C     | 13 ++++++++++++
 5 files changed, 41 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp0x/constexpr-nsdmi2.C
 create mode 100644 gcc/testsuite/g++.dg/cpp1z/lambda-this4.C

diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index e85b3c113f0..91f0c3ba269 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -5553,6 +5553,12 @@ cxx_eval_constant_expression (const constexpr_ctx *ctx, tree t,
 	tree init = TARGET_EXPR_INITIAL (t);
 	if ((AGGREGATE_TYPE_P (type) || VECTOR_TYPE_P (type)))
 	  {
+	    if (ctx->object)
+	      /* If the initializer contains any PLACEHOLDER_EXPR, we need to
+		 resolve them before we create a new CONSTRUCTOR for the
+		 temporary.  */
+	      init = replace_placeholders (init, ctx->object);
+
 	    /* We're being expanded without an explicit target, so start
 	       initializing a new object; expansion with an explicit target
 	       strips the TARGET_EXPR before we get here.  */
diff --git a/gcc/cp/tree.c b/gcc/cp/tree.c
index a2172dea0d8..5eb0dcd717a 100644
--- a/gcc/cp/tree.c
+++ b/gcc/cp/tree.c
@@ -3239,7 +3239,7 @@ replace_placeholders_r (tree* t, int* walk_subtrees, void* data_)
    a PLACEHOLDER_EXPR has been encountered.  */
 
 tree
-replace_placeholders (tree exp, tree obj, bool *seen_p)
+replace_placeholders (tree exp, tree obj, bool *seen_p /*= NULL*/)
 {
   /* This is only relevant for C++14.  */
   if (cxx_dialect < cxx14)
diff --git a/gcc/cp/typeck2.c b/gcc/cp/typeck2.c
index bff4ddbcf81..cf1cb5ace66 100644
--- a/gcc/cp/typeck2.c
+++ b/gcc/cp/typeck2.c
@@ -871,7 +871,7 @@ store_init_value (tree decl, tree init, vec<tree, va_gc>** cleanups, int flags)
     {
       bool const_init;
       tree oldval = value;
-      value = fold_non_dependent_expr (value);
+      value = fold_non_dependent_expr (value, tf_warning_or_error, true, decl);
       if (DECL_DECLARED_CONSTEXPR_P (decl)
 	  || (DECL_IN_AGGR_P (decl)
 	      && DECL_INITIALIZED_IN_CLASS_P (decl)))
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-nsdmi2.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-nsdmi2.C
new file mode 100644
index 00000000000..c51f734a134
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-nsdmi2.C
@@ -0,0 +1,20 @@
+// PR c++/94205
+// { dg-do compile { target c++14 } }
+
+struct S
+{
+  struct A
+  {
+    S *p;
+    constexpr A(S* p): p(p) {}
+    constexpr operator int() { p->i = 5; return 6; }
+  };
+  int i;
+  int a = A(this);
+};
+
+
+constexpr S s = {};
+
+#define SA(X) static_assert((X),#X)
+SA(s.i == 5 && s.a == 6);
diff --git a/gcc/testsuite/g++.dg/cpp1z/lambda-this4.C b/gcc/testsuite/g++.dg/cpp1z/lambda-this4.C
new file mode 100644
index 00000000000..5d968791491
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/lambda-this4.C
@@ -0,0 +1,13 @@
+// PR c++/94205
+// { dg-do compile { target c++17 } }
+
+struct S
+{
+  int i;
+  int a = [this] { this->i = 5; return 6; } ();
+};
+
+
+constexpr S s = {};
+
+static_assert (s.i == 5 && s.a == 6);

base-commit: f14b41d27124601284347a10d496362c8b4b8e1c
-- 
2.18.1