From fae627162d5f8cfb273b10349883eeb74baaa43f Mon Sep 17 00:00:00 2001
From: Iain Sandoe <iain@sandoe.co.uk>
Date: Mon, 27 Sep 2021 20:21:40 +0100
Subject: [PATCH] coroutines: Only set parm copy guard vars if we have
 exceptions [PR 102454].

For coroutines, we make copies of the original function arguments into
the coroutine frame.  Normally, these are destroyed on the proper exit
from the coroutine when the frame is destroyed.

However, if an exception is thrown before the first suspend point is
reached, the cleanup has to happen in the ramp function.  These cleanups
are guarded such that they are only applied to any param copies actually
made.

The ICE is caused by an attempt to set the guard variable when there are
no exceptions enabled (the guard var is not created in this case).

Fixed by checking for flag_exceptions in this case too.

While touching this code paths, also clean up the synthetic names used
when a function parm is unnamed.

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>

	PR c++/102454

gcc/cp/ChangeLog:

	* coroutines.cc (analyze_fn_parms): Clean up synthetic names for
	unnamed function params.
	(morph_fn_to_coro): Do not try to set a guard variable for param
	DTORs in the ramp, unless we have exceptions active.

gcc/testsuite/ChangeLog:

	* g++.dg/coroutines/pr102454.C: New test.
---
 gcc/cp/coroutines.cc                       | 25 +++++++++++---------
 gcc/testsuite/g++.dg/coroutines/pr102454.C | 38 ++++++++++++++++++++++++++++++
 2 files changed, 52 insertions(+), 11 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/coroutines/pr102454.C

diff --git a/gcc/cp/coroutines.cc b/gcc/cp/coroutines.cc
index fbd5c49..2f45575 100644
--- a/gcc/cp/coroutines.cc
+++ b/gcc/cp/coroutines.cc
@@ -3829,13 +3829,13 @@ analyze_fn_parms (tree orig)
 
       if (TYPE_HAS_NONTRIVIAL_DESTRUCTOR (parm.frame_type))
 	{
-	  char *buf = xasprintf ("_Coro_%s_live", IDENTIFIER_POINTER (name));
-	  parm.guard_var = build_lang_decl (VAR_DECL, get_identifier (buf),
-					    boolean_type_node);
+	  char *buf = xasprintf ("%s%s_live", DECL_NAME (arg) ? "_Coro_" : "",
+				 IDENTIFIER_POINTER (name));
+	  parm.guard_var
+	    = coro_build_artificial_var (UNKNOWN_LOCATION, get_identifier (buf),
+					 boolean_type_node, orig,
+					 boolean_false_node);
 	  free (buf);
-	  DECL_ARTIFICIAL (parm.guard_var) = true;
-	  DECL_CONTEXT (parm.guard_var) = orig;
-	  DECL_INITIAL (parm.guard_var) = boolean_false_node;
 	  parm.trivial_dtor = false;
 	}
       else
@@ -4843,11 +4843,14 @@ morph_fn_to_coro (tree orig, tree *resumer, tree *destroyer)
 					     NULL, parm.frame_type,
 					     LOOKUP_NORMAL,
 					     tf_warning_or_error);
-	      /* This var is now live.  */
-	      r = build_modify_expr (fn_start, parm.guard_var,
-				     boolean_type_node, INIT_EXPR, fn_start,
-				     boolean_true_node, boolean_type_node);
-	      finish_expr_stmt (r);
+	      if (flag_exceptions)
+		{
+		  /* This var is now live.  */
+		  r = build_modify_expr (fn_start, parm.guard_var,
+					 boolean_type_node, INIT_EXPR, fn_start,
+					 boolean_true_node, boolean_type_node);
+		  finish_expr_stmt (r);
+		}
 	    }
 	}
     }
diff --git a/gcc/testsuite/g++.dg/coroutines/pr102454.C b/gcc/testsuite/g++.dg/coroutines/pr102454.C
new file mode 100644
index 0000000..41aeda7
--- /dev/null
+++ b/gcc/testsuite/g++.dg/coroutines/pr102454.C
@@ -0,0 +1,38 @@
+//  { dg-additional-options "-fno-exceptions" }
+
+#include <coroutine>
+#include <string>
+
+template <typename T>
+struct looper {
+  struct promise_type {
+    auto get_return_object () { return handle_type::from_promise (*this); }
+    auto initial_suspend () { return suspend_always_prt {}; }
+    auto final_suspend () noexcept { return suspend_always_prt {}; }
+    void return_value (T);
+    void unhandled_exception ();
+  };
+
+  using handle_type = std::coroutine_handle<promise_type>;
+
+  looper (handle_type);
+
+  struct suspend_always_prt {
+    bool await_ready () noexcept;
+    void await_suspend (handle_type) noexcept;
+    void await_resume () noexcept;
+  };
+};
+
+template <typename T>
+looper<T>
+with_ctorable_state (T)
+{
+  co_return T ();
+}
+
+auto
+foo ()
+{
+  return with_ctorable_state<std::string>;
+}
-- 
2.7.4