[pushed] coroutines: Replace extra checks for co_yield with asserts.

[Iain Sandoe]

Hi,

The lowering of co_yield to a promise method call and a co_await
was moved to the initial analysis phase with the intention of
avoiding the need to handle the two cases later.

Before removing the later checks entirely, this patch replaces
them with checking asserts.

tested on x86-64-darwin16,
pushed to master as obvious,
thanks,
Iain

gcc/cp/Changelog:

2020-05-05  Iain Sandoe  <iain@sandoe.co.uk>

	* coroutines.cc (transform_await_wrapper): Check that we have
	no unlowered co_yields.
	(captures_temporary): Likewise.
	(register_awaits): Likewise.
---
 gcc/cp/ChangeLog     |  7 +++++++
 gcc/cp/coroutines.cc | 20 +++++++++++---------
 2 files changed, 18 insertions(+), 9 deletions(-)

diff --git a/gcc/cp/coroutines.cc b/gcc/cp/coroutines.cc
index 0c91abc84f2..ed871e1bab1 100644
--- a/gcc/cp/coroutines.cc
+++ b/gcc/cp/coroutines.cc
@@ -1743,7 +1743,9 @@ transform_await_wrapper (tree *stmt, int *do_subtree, void *d)
       && DECL_CONTEXT (*stmt) != xform->actor_fn)
     DECL_CONTEXT (*stmt) = xform->actor_fn;
 
-  if (TREE_CODE (*stmt) != CO_AWAIT_EXPR && TREE_CODE (*stmt) != CO_YIELD_EXPR)
+  /* We should have already lowered co_yields to their co_await.  */
+  gcc_checking_assert (TREE_CODE (*stmt) != CO_YIELD_EXPR);
+  if (TREE_CODE (*stmt) != CO_AWAIT_EXPR)
     return NULL_TREE;
 
   tree await_expr = *stmt;
@@ -2612,9 +2614,12 @@ struct susp_frame_data
 static tree
 captures_temporary (tree *stmt, int *do_subtree, void *d)
 {
+  /* We should have already lowered co_yields to their co_await.  */
+  gcc_checking_assert (TREE_CODE (*stmt) != CO_YIELD_EXPR);
+
   /* Stop recursing if we see an await expression, the subtrees
      of that will be handled when it is processed.  */
-  if (TREE_CODE (*stmt) == CO_AWAIT_EXPR || TREE_CODE (*stmt) == CO_YIELD_EXPR)
+  if (TREE_CODE (*stmt) == CO_AWAIT_EXPR)
     {
       *do_subtree = 0;
       return NULL_TREE;
@@ -2732,17 +2737,14 @@ register_awaits (tree *stmt, int *do_subtree ATTRIBUTE_UNUSED, void *d)
 {
   susp_frame_data *data = (susp_frame_data *) d;
 
-  if (TREE_CODE (*stmt) != CO_AWAIT_EXPR && TREE_CODE (*stmt) != CO_YIELD_EXPR)
+  /* We should have already lowered co_yields to their co_await.  */
+  gcc_checking_assert (TREE_CODE (*stmt) != CO_YIELD_EXPR);
+
+  if (TREE_CODE (*stmt) != CO_AWAIT_EXPR)
     return NULL_TREE;
 
   tree aw_expr = *stmt;
   location_t aw_loc = EXPR_LOCATION (aw_expr); /* location of the co_xxxx.  */
-  /* co_yield is syntactic sugar, re-write it to co_await.  */
-  if (TREE_CODE (aw_expr) == CO_YIELD_EXPR)
-    {
-      aw_expr = TREE_OPERAND (aw_expr, 1);
-      *stmt = aw_expr;
-    }
 
   /* If the awaitable is a parm or a local variable, then we already have
      a frame copy, so don't make a new one.  */
-- 
2.24.1