[PATCH] [PR rtl-optimization/65618] Fix MIPS ADA bootstrap failure

[James Cowgill]

Hi,

This patch fixes PR 65618 where ADA cannot be bootstrapped natively on
mips due to a bootstrap comparison failure. The PR is currently in the
target component, but should be in the rtl-optimization component.

The underlying bug is in gcc/emit-rtl.c:try_split and is a result of
the fix for PR rtl-optimization/48826. In that PR, if a call_insn is
split into two instructions, the following NOTE_INSN_CALL_ARG_LOCATION
is moved so that it immediately follows the new call_insn. However,
after doing that the "after" variable was not updated and it could
still point to the old note instruction (the instruction after the
instruction to be split). The "after" variable is later used to obtain
the last instruction in the split and is then passed back to the
delayed branch scheduler influencing how delay slots are assigned. My
patch adjusts the code which handles the NOTE_INSN_CALL_ARG_LOCATION
note so that "after" is updated if necessary.

This bug causes the ADA bootstrap comparison failure in a-except.o
because the branch delay scheduling operates slightly differently for
that file if debug information is turned on.

Thanks,
James

gcc/Changelog:

2016-12-16  James Cowgill  <James.Cowgill@imgtec.com>

	PR rtl-optimization/65618
	* emit-rtl.c (try_split): Update "after" when moving a
	NOTE_INSN_CALL_ARG_LOCATION.

diff --git a/gcc/emit-rtl.c b/gcc/emit-rtl.c
index 7de17454037..6be124ac038 100644
--- a/gcc/emit-rtl.c
+++ b/gcc/emit-rtl.c
@@ -3742,6 +3742,11 @@ try_split (rtx pat, rtx_insn *trial, int last)
 		   next = NEXT_INSN (next))
 		if (NOTE_KIND (next) == NOTE_INSN_CALL_ARG_LOCATION)
 		  {
+		    /* Advance after to the next instruction if it is about to
+		       be removed.  */
+		    if (after == next)
+		      after = NEXT_INSN (after);
+
 		    remove_insn (next);
 		    add_insn_after (next, insn, NULL);
 		    break;