diff --git a/gcc/Makefile.in b/gcc/Makefile.in
index 61b512c9b7..0849ce4826 100644
--- a/gcc/Makefile.in
+++ b/gcc/Makefile.in
@@ -1265,6 +1265,7 @@ OBJS = \
 	compare-elim.o \
 	context.o \
 	convert.o \
+	coroutine-passes.o \
 	coverage.o \
 	cppbuiltin.o \
 	cppdefault.o \
diff --git a/gcc/coroutine-passes.cc b/gcc/coroutine-passes.cc
new file mode 100644
index 0000000000..d032a392ce
--- /dev/null
+++ b/gcc/coroutine-passes.cc
@@ -0,0 +1,532 @@
+/* coroutine expansion and optimisation passes.
+
+   Copyright (C) 2018-2020 Free Software Foundation, Inc.
+
+ Contributed by Iain Sandoe <iain@sandoe.co.uk> under contract to Facebook.
+
+This file is part of GCC.
+
+GCC is free software; you can redistribute it and/or modify it under
+the terms of the GNU General Public License as published by the Free
+Software Foundation; either version 3, or (at your option) any later
+version.
+
+GCC is distributed in the hope that it will be useful, but WITHOUT ANY
+WARRANTY; without even the implied warranty of MERCHANTABILITY or
+FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+for more details.
+
+You should have received a copy of the GNU General Public License
+along with GCC; see the file COPYING3.  If not see
+<http://www.gnu.org/licenses/>.  */
+
+#include "config.h"
+#include "system.h"
+#include "coretypes.h"
+#include "backend.h"
+#include "target.h"
+#include "tree.h"
+#include "gimple.h"
+#include "tree-pass.h"
+#include "ssa.h"
+#include "cgraph.h"
+#include "pretty-print.h"
+#include "diagnostic-core.h"
+#include "fold-const.h"
+#include "internal-fn.h"
+#include "langhooks.h"
+#include "gimplify.h"
+#include "gimple-iterator.h"
+#include "gimplify-me.h"
+#include "gimple-walk.h"
+#include "gimple-fold.h"
+#include "tree-cfg.h"
+#include "tree-into-ssa.h"
+#include "tree-ssa-propagate.h"
+#include "gimple-pretty-print.h"
+#include "cfghooks.h"
+
+/* Here we:
+   * lower the internal function that implements an exit from scope.
+   * expand the builtins that are used to implement the library
+     interfaces to the coroutine frame.  */
+
+static tree
+lower_coro_builtin (gimple_stmt_iterator *gsi, bool *handled_ops_p,
+		    struct walk_stmt_info *wi ATTRIBUTE_UNUSED)
+{
+  gimple *stmt = gsi_stmt (*gsi);
+  *handled_ops_p = !gimple_has_substatements (stmt);
+
+  if (gimple_code (stmt) != GIMPLE_CALL)
+    return NULL_TREE;
+
+  /* This internal function implements an exit from scope without
+     performing any cleanups; it jumps directly to the label provided.  */
+  if (gimple_call_internal_p (stmt)
+      && gimple_call_internal_fn (stmt) == IFN_CO_SUSPN)
+    {
+      tree dest = TREE_OPERAND (gimple_call_arg (stmt, 0), 0);
+      ggoto *g = gimple_build_goto (dest);
+      gsi_replace (gsi, g, /* do EH */ false);
+      *handled_ops_p = true;
+      return NULL_TREE;
+    }
+
+  tree decl = gimple_call_fndecl (stmt);
+  if (!decl || !fndecl_built_in_p (decl, BUILT_IN_NORMAL))
+    return NULL_TREE;
+
+  /* The remaining builtins implement the library interfaces to the coro
+     frame.  */
+  unsigned call_idx = 0;
+
+  switch (DECL_FUNCTION_CODE (decl))
+    {
+    default:
+      break;
+    case BUILT_IN_CORO_PROMISE:
+      {
+	/* If we are discarding this, then skip it; the function has no
+	   side-effects.  */
+	tree lhs = gimple_call_lhs (stmt);
+	if (!lhs)
+	  {
+	    gsi_remove (gsi, true);
+	    *handled_ops_p = true;
+	    return NULL_TREE;
+	  }
+	/* The coro frame starts with two pointers (to the resume and
+	   destroy() functions).  These are followed by the promise which
+	   is aligned as per type [or user attribute].
+	   The input pointer is the first argument.
+	   The promise alignment is the second and the third is a bool
+	   that is true when we are converting from a promise ptr to a
+	   frame pointer, and false for the inverse.  */
+	tree ptr = gimple_call_arg (stmt, 0);
+	tree align_t = gimple_call_arg (stmt, 1);
+	tree from = gimple_call_arg (stmt, 2);
+	gcc_checking_assert (TREE_CODE (align_t) == INTEGER_CST);
+	gcc_checking_assert (TREE_CODE (from) == INTEGER_CST);
+	bool dir = wi::to_wide (from) != 0;
+	HOST_WIDE_INT promise_align = TREE_INT_CST_LOW (align_t);
+	HOST_WIDE_INT psize =
+	  TREE_INT_CST_LOW (TYPE_SIZE_UNIT (ptr_type_node));
+	HOST_WIDE_INT align = TYPE_ALIGN_UNIT (ptr_type_node);
+	align = MAX (align, promise_align);
+	psize *= 2; /* Start with two pointers.  */
+	psize = ROUND_UP (psize, align);
+	HOST_WIDE_INT offs = dir ? -psize : psize;
+	tree repl = build2 (POINTER_PLUS_EXPR, ptr_type_node, ptr,
+			    size_int (offs));
+	gassign *grpl = gimple_build_assign (lhs, repl);
+	gsi_replace (gsi, grpl, true);
+	*handled_ops_p = true;
+      }
+      break;
+    case BUILT_IN_CORO_DESTROY:
+      call_idx = 1;
+      /* FALLTHROUGH */
+    case BUILT_IN_CORO_RESUME:
+      {
+	tree ptr = gimple_call_arg (stmt, 0); /* frame ptr.  */
+	HOST_WIDE_INT psize =
+	  TREE_INT_CST_LOW (TYPE_SIZE_UNIT (ptr_type_node));
+	HOST_WIDE_INT offset = call_idx * psize;
+	tree fntype = TREE_TYPE (decl);
+	tree fntype_ptr = build_pointer_type (fntype);
+	tree fntype_ppp = build_pointer_type (fntype_ptr);
+	tree indirect = fold_build2 (MEM_REF, fntype_ptr, ptr,
+				     build_int_cst (fntype_ppp, offset));
+	tree f_ptr_tmp = make_ssa_name (TYPE_MAIN_VARIANT (fntype_ptr));
+	gassign *get_fptr = gimple_build_assign (f_ptr_tmp, indirect);
+	gsi_insert_before (gsi, get_fptr, GSI_SAME_STMT);
+	gimple_call_set_fn (static_cast<gcall *> (stmt), f_ptr_tmp);
+	*handled_ops_p = true;
+      }
+      break;
+    case BUILT_IN_CORO_DONE:
+      {
+	/* If we are discarding this, then skip it; the function has no
+	   side-effects.  */
+	tree lhs = gimple_call_lhs (stmt);
+	if (!lhs)
+	  {
+	    gsi_remove (gsi, true);
+	    *handled_ops_p = true;
+	    return NULL_TREE;
+	  }
+	/* When we're done, the resume fn is set to NULL.  */
+	tree ptr = gimple_call_arg (stmt, 0); /* frame ptr.  */
+	tree vpp = build_pointer_type (ptr_type_node);
+	tree indirect
+	  = fold_build2 (MEM_REF, vpp, ptr, build_int_cst (vpp, 0));
+	tree d_ptr_tmp = make_ssa_name (ptr_type_node);
+	gassign *get_dptr = gimple_build_assign (d_ptr_tmp, indirect);
+	gsi_insert_before (gsi, get_dptr, GSI_SAME_STMT);
+	tree done = fold_build2 (EQ_EXPR, boolean_type_node, d_ptr_tmp,
+				 null_pointer_node);
+	gassign *get_res = gimple_build_assign (lhs, done);
+	gsi_replace (gsi, get_res, true);
+	*handled_ops_p = true;
+      }
+      break;
+    }
+  return NULL_TREE;
+}
+
+/* Main entry point for lowering coroutine FE builtins.  */
+
+static unsigned int
+execute_lower_coro_builtins (void)
+{
+  struct walk_stmt_info wi;
+  gimple_seq body;
+
+  body = gimple_body (current_function_decl);
+  memset (&wi, 0, sizeof (wi));
+  walk_gimple_seq_mod (&body, lower_coro_builtin, NULL, &wi);
+  gimple_set_body (current_function_decl, body);
+
+  return 0;
+}
+
+namespace {
+
+const pass_data pass_data_coroutine_lower_builtins = {
+  GIMPLE_PASS,		 /* type */
+  "coro-lower-builtins", /* name */
+  OPTGROUP_NONE,	 /* optinfo_flags */
+  TV_NONE,		 /* tv_id */
+  0,			 /* properties_required */
+  0,			 /* properties_provided */
+  0,			 /* properties_destroyed */
+  0,			 /* todo_flags_start */
+  0			 /* todo_flags_finish */
+};
+
+class pass_coroutine_lower_builtins : public gimple_opt_pass
+{
+public:
+  pass_coroutine_lower_builtins (gcc::context *ctxt)
+    : gimple_opt_pass (pass_data_coroutine_lower_builtins, ctxt)
+  {}
+
+  /* opt_pass methods: */
+  virtual bool gate (function *) { return flag_coroutines; };
+
+  virtual unsigned int execute (function *f ATTRIBUTE_UNUSED)
+  {
+    return execute_lower_coro_builtins ();
+  }
+
+}; // class pass_coroutine_lower_builtins
+
+} // namespace
+
+gimple_opt_pass *
+make_pass_coroutine_lower_builtins (gcc::context *ctxt)
+{
+  return new pass_coroutine_lower_builtins (ctxt);
+}
+
+/* Expand the remaining coroutine IFNs.
+
+   In the front end we construct a single actor function that contains
+   the coroutine state machine.
+
+   The actor function has three entry conditions:
+    1. from the ramp, resume point 0 - to initial-suspend.
+    2. when resume () is executed (resume point N).
+    3. from the destroy () shim when that is executed.
+
+   The actor function begins with two dispatchers; one for resume and
+   one for destroy (where the initial entry from the ramp is a special-
+   case of resume point 0).
+
+   Each suspend point and each dispatch entry is marked with an IFN such
+   that we can connect the relevant dispatchers to their target labels.
+
+   So, if we have:
+
+   CO_YIELD (NUM, FINAL, RES_LAB, DEST_LAB, FRAME_PTR)
+
+   This is await point NUM, and is the final await if FINAL is non-zero.
+   The resume point is RES_LAB, and the destroy point is DEST_LAB.
+
+   We expect to find a CO_ACTOR (NUM) in the resume dispatcher and a
+   CO_ACTOR (NUM+1) in the destroy dispatcher.
+
+   Initially, the intent of keeping the resume and destroy paths together
+   is that the conditionals controlling them are identical, and thus there
+   would be duplication of any optimisation of those paths if the split
+   were earlier.
+
+   Subsequent inlining of the actor (and DCE) is then able to extract the
+   resume and destroy paths as separate functions if that is found
+   profitable by the optimisers.
+
+   Once we have remade the connections to their correct postions, we elide
+   the labels that the front end inserted.  */
+
+static void
+move_edge_and_update (edge e, basic_block old_bb, basic_block new_bb)
+{
+  if (dump_file)
+    fprintf (dump_file, "redirecting edge from bb %u to bb %u\n", old_bb->index,
+	     new_bb->index);
+
+  e = redirect_edge_and_branch (e, new_bb);
+  if (!e && dump_file)
+    fprintf (dump_file, "failed to redirect edge ..  \n");
+
+  /* Die if we failed.  */
+  gcc_checking_assert (e);
+}
+
+static unsigned int
+execute_early_expand_coro_ifns (void)
+{
+  /* Don't rebuild stuff unless we have to. */
+  unsigned int todoflags = 0;
+  bool changed = false;
+  /* Some of the possible YIELD points will hopefully have been removed by
+     earlier optimisations; record the ones that are still present.  */
+  hash_map<int_hash<HOST_WIDE_INT, -1, -2>, tree> destinations;
+  /* Labels we added to carry the CFG changes, we need to remove these to
+     avoid confusing EH.  */
+  hash_set<tree> to_remove;
+  /* List of dispatch points to update.  */
+  auto_vec<gimple_stmt_iterator, 16> actor_worklist;
+  basic_block bb;
+  gimple_stmt_iterator gsi;
+
+  FOR_EACH_BB_FN (bb, cfun)
+    for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi);)
+      {
+	gimple *stmt = gsi_stmt (gsi);
+
+	if (!is_gimple_call (stmt) || !gimple_call_internal_p (stmt))
+	  {
+	    gsi_next (&gsi);
+	    continue;
+	  }
+	switch (gimple_call_internal_fn (stmt))
+	  {
+	  case IFN_CO_FRAME:
+	    {
+	      /* This internal function is a placeholder for the frame
+		 size.  In principle, we might lower it later (after some
+		 optimisation had reduced the frame size).  At present,
+		 without any such optimisation, we just set it here.  */
+	      tree lhs = gimple_call_lhs (stmt);
+	      tree size = gimple_call_arg (stmt, 0);
+	      /* Right now, this is a trivial operation - copy through
+		 the size computed during initial layout.  */
+	      gassign *grpl = gimple_build_assign (lhs, size);
+	      gsi_replace (&gsi, grpl, true);
+	      gsi_next (&gsi);
+	    }
+	    break;
+	  case IFN_CO_ACTOR:
+	    changed = true;
+	    actor_worklist.safe_push (gsi); /* Save for later.  */
+	    gsi_next (&gsi);
+	    break;
+	  case IFN_CO_YIELD:
+	    {
+	      changed = true;
+	      /* .CO_YIELD (NUM, FINAL, RES_LAB, DEST_LAB, FRAME_PTR);
+		  NUM = await number.
+		  FINAL = 1 if this is the final_suspend() await.
+		  RES_LAB = resume point label.
+		  DEST_LAB = destroy point label.
+		  FRAME_PTR = is a null pointer with the type of the coro
+			      frame, so that we can resize, if needed.  */
+	      if (dump_file)
+		fprintf (dump_file, "saw CO_YIELD in BB %u\n", bb->index);
+	      tree num = gimple_call_arg (stmt, 0); /* yield point.  */
+	      HOST_WIDE_INT idx = TREE_INT_CST_LOW (num);
+	      bool existed;
+	      tree res_tgt = TREE_OPERAND (gimple_call_arg (stmt, 2), 0);
+	      tree &res_dest = destinations.get_or_insert (idx, &existed);
+	      if (existed && dump_file)
+		{
+		  fprintf (
+		    dump_file,
+		    "duplicate YIELD RESUME point (" HOST_WIDE_INT_PRINT_DEC
+		    ") ?\n",
+		    idx);
+		  print_gimple_stmt (dump_file, stmt, 0, TDF_VOPS|TDF_MEMSYMS);
+		}
+	      else
+		res_dest = res_tgt;
+	      tree dst_tgt = TREE_OPERAND (gimple_call_arg (stmt, 3), 0);
+	      tree &dst_dest = destinations.get_or_insert (idx + 1, &existed);
+	      if (existed && dump_file)
+		{
+		  fprintf (
+		    dump_file,
+		    "duplicate YIELD DESTROY point (" HOST_WIDE_INT_PRINT_DEC
+		    ") ?\n",
+		    idx + 1);
+		  print_gimple_stmt (dump_file, stmt, 0, TDF_VOPS|TDF_MEMSYMS);
+		}
+	      else
+		dst_dest = dst_tgt;
+	      to_remove.add (res_tgt);
+	      to_remove.add (dst_tgt);
+	      /* lose the co_yield.  */
+	      gsi_remove (&gsi, true);
+	      stmt = gsi_stmt (gsi); /* next. */
+	      /* lose the copy present at O0.  */
+	      if (is_gimple_assign (stmt))
+		{
+		  gsi_remove (&gsi, true);
+		  stmt = gsi_stmt (gsi);
+		}
+	      /* Simplify the switch or if following.  */
+	      if (gswitch *gsw = dyn_cast<gswitch *> (stmt))
+		{
+		  gimple_switch_set_index (gsw, integer_zero_node);
+		  fold_stmt (&gsi);
+		}
+	      else if (gcond *gif = dyn_cast<gcond *> (stmt))
+		{
+		  if (gimple_cond_code (gif) == EQ_EXPR)
+		    gimple_cond_make_true (gif);
+		  else
+		    gimple_cond_make_false (gif);
+		  fold_stmt (&gsi);
+		}
+	      else if (dump_file)
+		print_gimple_stmt (dump_file, stmt, 0, TDF_VOPS|TDF_MEMSYMS);
+	      if (gsi_end_p (gsi))
+		break;
+	      continue;
+	    }
+	  default:
+	    gsi_next (&gsi);
+	    break;
+	  }
+      }
+
+  if (!changed)
+    {
+      if (dump_file)
+	fprintf (dump_file, "coro: nothing to do\n");
+      return todoflags;
+    }
+
+  while (!actor_worklist.is_empty ())
+    {
+      gsi = actor_worklist.pop ();
+      gimple *stmt = gsi_stmt (gsi);
+      gcc_checking_assert (is_gimple_call (stmt)
+			   && gimple_call_internal_p (stmt)
+			   && gimple_call_internal_fn (stmt) == IFN_CO_ACTOR);
+      bb = gsi_bb (gsi);
+      HOST_WIDE_INT idx = TREE_INT_CST_LOW (gimple_call_arg (stmt, 0));
+      tree *seen = destinations.get (idx);
+      changed = true;
+
+      if (dump_file)
+	fprintf (dump_file, "saw CO_ACTOR in BB %u\n", bb->index);
+
+      if (!seen)
+	{
+	  /* If we never saw this index, it means that the CO_YIELD
+	  associated was elided during earlier optimisations, so we
+	  don't need to fix up the switch targets.  */
+	  if (dump_file)
+	    fprintf (dump_file, "yield point " HOST_WIDE_INT_PRINT_DEC
+		     " not used, removing it .. \n",  idx);
+	  gsi_remove (&gsi, true);
+	  release_defs (stmt);
+	}
+      else
+	{
+	  /* So we need to switch the target of this switch case to the
+	     relevant BB.  */
+	  basic_block new_bb = label_to_block (cfun, *seen);
+	  /* We expect the block we're modifying to contain a single
+	     CO_ACTOR() followed by a goto <switch default bb>.  */
+	  gcc_checking_assert (EDGE_COUNT (bb->succs) == 1);
+	  edge e;
+	  edge_iterator ei;
+	  FOR_EACH_EDGE (e, ei, bb->succs)
+	    {
+	      basic_block old_bb = e->dest;
+	      move_edge_and_update (e, old_bb, new_bb);
+	    }
+	  gsi_remove (&gsi, true);
+	}
+    }
+
+  /* Remove the labels we inserted to map our hidden CFG, this
+     avoids confusing block merges when there are also EH labels.  */
+  FOR_EACH_BB_FN (bb, cfun)
+    for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi);)
+      {
+	gimple *stmt = gsi_stmt (gsi);
+	if (glabel *glab = dyn_cast<glabel *> (stmt))
+	  {
+	    tree rem = gimple_label_label (glab);
+	    if (to_remove.contains (rem))
+	      {
+		gsi_remove (&gsi, true);
+		to_remove.remove (rem);
+		continue; /* We already moved to the next insn.  */
+	      }
+	  }
+	else
+	  break;
+	gsi_next (&gsi);
+      }
+
+  /* Changed the CFG.  */
+  todoflags |= TODO_cleanup_cfg;
+  return todoflags;
+}
+
+namespace {
+
+const pass_data pass_data_coroutine_early_expand_ifns = {
+  GIMPLE_PASS,		    /* type */
+  "coro-early-expand-ifns", /* name */
+  OPTGROUP_NONE,	    /* optinfo_flags */
+  TV_NONE,		    /* tv_id */
+  (PROP_cfg),		    /* properties_required */
+  0,			    /* properties_provided */
+  0,			    /* properties_destroyed */
+  0,			    /* todo_flags_start */
+  0			    /* todo_flags_finish, set this in the fn. */
+};
+
+class pass_coroutine_early_expand_ifns : public gimple_opt_pass
+{
+public:
+  pass_coroutine_early_expand_ifns (gcc::context *ctxt)
+    : gimple_opt_pass (pass_data_coroutine_early_expand_ifns, ctxt)
+  {}
+
+  /* opt_pass methods: */
+  virtual bool gate (function *f)
+    {
+      return flag_coroutines && f->coroutine_component;
+    }
+
+  virtual unsigned int execute (function *f ATTRIBUTE_UNUSED)
+  {
+    return execute_early_expand_coro_ifns ();
+  }
+
+}; // class pass_coroutine_expand_ifns
+
+} // namespace
+
+gimple_opt_pass *
+make_pass_coroutine_early_expand_ifns (gcc::context *ctxt)
+{
+  return new pass_coroutine_early_expand_ifns (ctxt);
+}
diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index 41c14001fd..6093613bae 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -16802,6 +16802,9 @@ emit_coro_helper (tree helper)
   cp_fold_function (helper);
   DECL_CONTEXT (DECL_RESULT (helper)) = helper;
   BLOCK_SUPERCONTEXT (DECL_INITIAL (helper)) = helper;
+  /* This function has coroutine IFNs that we should handle in middle
+     end lowering.  */
+  cfun->coroutine_component = true;
   cp_genericize (helper);
   expand_or_defer_fn (helper);
 }
@@ -16858,6 +16861,9 @@ finish_function (bool inline_p)
 	  return fndecl;
 	}
 
+      /* We should handle coroutine IFNs in middle end lowering.  */
+      cfun->coroutine_component = true;
+
       if (use_eh_spec_block (fndecl))
 	finish_eh_spec_block (TYPE_RAISES_EXCEPTIONS
 			      (TREE_TYPE (fndecl)),
diff --git a/gcc/function.h b/gcc/function.h
index 496d3f728c..1ee8ed3de5 100644
--- a/gcc/function.h
+++ b/gcc/function.h
@@ -418,6 +418,9 @@ struct GTY(()) function {
   /* Set when the function was compiled with generation of debug
      (begin stmt, inline entry, ...) markers enabled.  */
   unsigned int debug_nonbind_markers : 1;
+
+  /* Set if this is a coroutine-related function.  */
+  unsigned int coroutine_component : 1;
 };
 
 /* Add the decl D to the local_decls list of FUN.  */
diff --git a/gcc/passes.def b/gcc/passes.def
index b6bd4f3d31..2db4ef4acc 100644
--- a/gcc/passes.def
+++ b/gcc/passes.def
@@ -39,8 +39,10 @@ along with GCC; see the file COPYING3.  If not see
   NEXT_PASS (pass_lower_tm);
   NEXT_PASS (pass_refactor_eh);
   NEXT_PASS (pass_lower_eh);
+  NEXT_PASS (pass_coroutine_lower_builtins);
   NEXT_PASS (pass_build_cfg);
   NEXT_PASS (pass_warn_function_return);
+  NEXT_PASS (pass_coroutine_early_expand_ifns);
   NEXT_PASS (pass_expand_omp);
   NEXT_PASS (pass_warn_printf);
   NEXT_PASS (pass_walloca, /*strict_mode_p=*/true);
diff --git a/gcc/tree-pass.h b/gcc/tree-pass.h
index 5ff43572b8..f10f467462 100644
--- a/gcc/tree-pass.h
+++ b/gcc/tree-pass.h
@@ -478,6 +478,8 @@ extern gimple_opt_pass *make_pass_gen_hsail (gcc::context *ctxt);
 extern gimple_opt_pass *make_pass_warn_nonnull_compare (gcc::context *ctxt);
 extern gimple_opt_pass *make_pass_sprintf_length (gcc::context *ctxt);
 extern gimple_opt_pass *make_pass_walloca (gcc::context *ctxt);
+extern gimple_opt_pass *make_pass_coroutine_lower_builtins (gcc::context *ctxt);
+extern gimple_opt_pass *make_pass_coroutine_early_expand_ifns (gcc::context *ctxt);
 
 /* IPA Passes */
 extern simple_ipa_opt_pass *make_pass_ipa_lower_emutls (gcc::context *ctxt);
