* basic-block.h (could_fall_through): Declare.

	* cfganal.c (can_fallthru): Succeed if the target is EXIT_BLOCK_PTR.
	Fail if the source already has a fallthrough edge to the exit
	block pointer.
	(could_fall_through): New function.
	* cfgbuild.c (make_edges): Check if we already have a fallthrough
	edge to the exit block pointer.
	* cfglayout.c (fixup_fallthru_exit_predecessor): Check that it is
	not called before reload has completed.
	Handle special case of first block having a fall-through exit edge.
	(cfg_layout_finalize): Don't call it before reload or if we have
	rtl epilogues.
	(fixup_reorder_chain): A fall through to the exit block does not
	require the block to come last.  Add sanity checks.
	* cfgrtl.c (rtl_split_edge): Add special handling of fall through
	edges to the exit block.
	* function.c (cfglayout.h): #include.
	(thread_prologue_and_epilogue_insns): If we have neither return nor
	epilogue, but a fall through to the exit block from mid-function,
	force a non-fall-through exit.
	* Makefile.in (function.o): Depend on CFGLAYOUT_H.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@83089 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 26 insertions, 1 deletions

diff --git a/gcc/cfganal.c b/gcc/cfganal.c
index 1a7d280513f..c8675dca6e2 100644
--- a/gcc/cfganal.c
+++ b/gcc/cfganal.c
@@ -103,17 +103,42 @@ bool
 can_fallthru (basic_block src, basic_block target)
 {
   rtx insn = BB_END (src);
-  rtx insn2 = target == EXIT_BLOCK_PTR ? NULL : BB_HEAD (target);
+  rtx insn2;
+  edge e;
 
+  if (target == EXIT_BLOCK_PTR)
+    return true;
   if (src->next_bb != target)
     return 0;
+  for (e = src->succ; e; e = e->succ_next)
+    if (e->dest == EXIT_BLOCK_PTR
+	&& e->flags & EDGE_FALLTHRU)
+    return 0;
 
+  insn2 = BB_HEAD (target);
   if (insn2 && !active_insn_p (insn2))
     insn2 = next_active_insn (insn2);
 
   /* ??? Later we may add code to move jump tables offline.  */
   return next_active_insn (insn) == insn2;
 }
+
+/* Return nonzero if we could reach target from src by falling through,
+   if the target was made adjacent.  If we already have a fall-through
+   edge to the exit block, we can't do that.  */
+bool
+could_fall_through (basic_block src, basic_block target)
+{
+  edge e;
+
+  if (target == EXIT_BLOCK_PTR)
+    return true;
+  for (e = src->succ; e; e = e->succ_next)
+    if (e->dest == EXIT_BLOCK_PTR
+	&& e->flags & EDGE_FALLTHRU)
+    return 0;
+  return true;
+}
 
 /* Mark the back edges in DFS traversal.
    Return nonzero if a loop (natural or otherwise) is present.