Inserts use of return register in epilogue threading, to keep
representation consistent, and prevent mismatch in crossjump matching.
Thanks,
- Tom
Index: gcc/function.c
===================================================================
--- gcc/function.c (revision 170556)
+++ gcc/function.c (working copy)
@@ -5241,6 +5241,19 @@ prologue_epilogue_contains (const_rtx in
return 0;
}
+/* Insert use of return register before the end of BB. */
+
+static void
+emit_use_return_register_into_block (basic_block bb)
+{
+ rtx seq;
+ start_sequence ();
+ use_return_register ();
+ seq = get_insns ();
+ end_sequence ();
+ emit_insn_before (seq, BB_END (bb));
+}
+
#ifdef HAVE_return
/* Insert gen_return at the end of block BB. This also means updating
block_for_insn appropriately. */
@@ -5395,6 +5408,15 @@ thread_prologue_and_epilogue_insns (void
with a simple return instruction. */
if (simplejump_p (jump))
{
+ /* The use of the return register might be present in the exit
+ fallthru block. Either:
+ - removing the use is safe, and we should remove the use in
+ the exit fallthru block, or
+ - removing the use is not safe, and we should add it here.
+ For now, we conservatively choose the latter. Either of the
+ 2 helps in crossjumping. */
+ emit_use_return_register_into_block (bb);
+
emit_return_into_block (bb);
delete_insn (jump);
}
@@ -5409,6 +5431,9 @@ thread_prologue_and_epilogue_insns (void
continue;
}
+ /* See comment in simple_jump_p case above. */
+ emit_use_return_register_into_block (bb);
+
/* If this block has only one successor, it both jumps
and falls through to the fallthru block, so we can't
delete the edge. */
