[compare-debug] use call loc for nop_endbr

[Alexandre Oliva <aoliva at redhat dot com>]

We skip debug insns and notes after a call that needs a nop_endbr, but
since a debug insn could be the last in a block, it may affect the loc
in the emitted nop_endbr insn.  Although this has no effect on
codegen, it does mess with debug info a bit, and it causes
-fcompare-debug to fail for e.g. libsanitizer's
tsan/tsan_platform_linux.cc on x86_64.

So, pick the location of the call insn for the nop_endbr insn, to
avoid the line number differences in dumps, including -fcompare-debug
ones.

Also, we don't need to determine what the insert point would be unless
we're actually emitting the nop_endbr insn after the call, so
rearrange the code to avoid wasting cycles.

Finally, it seems like testing for barriers is a mistake.  We probably
never actually pass that test, for the barriers would hit BB_END
first.  If we did, we'd end up emitting the nop_endbr outside any BB,
even after the end of the function!  That would be Very Bad (TM).
Now, since the test as it is can't hurt, I figured I wouldn't change
the logic right now, just add a comment so that someone involved in
endbr stuff can have a second look and hopefully fix it.

I'd appreciate if you'd try to drop the BARRIER_P from the loop test,
Igor, so as to address the final ??? in the comment I add.  Narrowing
the skipped notes to only the relevant post-call ones might make sense
as well, but it's not quite as important IMHO.

Regstrapping with -fcompare-debug on stage3 host and target builds on
x86_64- and i686-linux-gnu; ok to install?

for  gcc/ChangeLog

	* config/i386/i386.c (rest_of_insert_endbranch): Use call loc
	for its nop_endbr.
---
 gcc/config/i386/i386.c |   20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
index e323102cef59..8960b966b7fc 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -2609,21 +2609,25 @@ rest_of_insert_endbranch (void)
 	{
 	  if (INSN_P (insn) && GET_CODE (insn) == CALL_INSN)
 	    {
-	      rtx_insn *next_insn = insn;
+	      if (find_reg_note (insn, REG_SETJMP, NULL) == NULL)
+		continue;
+	      /* Generate ENDBRANCH after CALL, which can return more than
+		 twice, setjmp-like functions.  */
 
+	      /* Skip notes and debug insns that must be next to the
+		 call insn.  ??? This might skip a lot more than
+		 that...  ??? Skipping barriers and emitting code
+		 after them surely looks like a mistake; we probably
+		 won't ever hit it, for we'll hit BB_END first.  */
+	      rtx_insn *next_insn = insn;
 	      while ((next_insn != BB_END (bb))
 		      && (DEBUG_INSN_P (NEXT_INSN (next_insn))
 			  || NOTE_P (NEXT_INSN (next_insn))
 			  || BARRIER_P (NEXT_INSN (next_insn))))
 		next_insn = NEXT_INSN (next_insn);
 
-	      /* Generate ENDBRANCH after CALL, which can return more than
-		 twice, setjmp-like functions.  */
-	      if (find_reg_note (insn, REG_SETJMP, NULL) != NULL)
-		{
-		  cet_eb = gen_nop_endbr ();
-		  emit_insn_after (cet_eb, next_insn);
-		}
+	      cet_eb = gen_nop_endbr ();
+	      emit_insn_after_setloc (cet_eb, next_insn, INSN_LOCATION (insn));
 	      continue;
 	    }
 

-- 
Alexandre Oliva, freedom fighter    http://FSFLA.org/~lxoliva/
You must be the change you wish to see in the world. -- Gandhi
Be Free! -- http://FSFLA.org/   FSF Latin America board member
Free Software Evangelist|Red Hat Brasil GNU Toolchain Engineer