Re: Fix Eh delivery in partitioned functions

[Jan Hubicka <hubicka@ucw.cz>]

> > I think we could just output from generic code - I think it can be done by
> > final_scan_insn. I don't know however if we have a way to tell if the section
> > starts with a landing pad?
> 
> Not sure either -- some insn note / bb note?  Some flag on the label?
> At least the latter should be easy to add if it's not there already.
> 
> Richard.

Hi,
this is updated patch.  I am now adding NOP_EXPR into the instruction stream.
This is done before shorten branches so alignment tracking works there as
expected. 
Landing pads are having PRESERVE flag set, but that is also true about named
labels etc.  So I think only safe way is to look them up from the EH tables
which is not that hard.  first_in_partition is now called on every landing
pad in the cold section and it walks backward looking if it can be first.  I added
visited set to be sure it runs in linear time.

Boostrapped/regtested x86_64-linux, OK?

Honza

	* except.c (first_in_partition): New function.
	(maybe_add_nop_after_section_switch): New function.
	* except.h (maybe_add_nop_after_section_switch): Declare.
	* final.c (rest_of_handle_shorten_branches): Use it.
Index: except.c
===================================================================
--- except.c	(revision 250312)
+++ except.c	(working copy)
@@ -2724,6 +2724,60 @@ sjlj_size_of_call_site_table (void)
   return size;
 }
 
+/* If L is first in the partition return NOTE_INSN_SWITCH_TEXT_SECTIONS
+   note which starts the section.  */
+rtx_insn *
+first_in_partition (rtx_insn *l, hash_set<rtx_insn *> *visited)
+{
+  while (l != NULL_RTX)
+    {
+      if (visited->add (l))
+	return NULL;
+      if (active_insn_p (l)
+	  && GET_CODE (PATTERN (l)) != ASM_INPUT
+	  && GET_CODE (PATTERN (l)) != ASM_OPERANDS)
+	return NULL; 
+      else if (GET_CODE (l) == NOTE
+	       && NOTE_KIND (l) == NOTE_INSN_SWITCH_TEXT_SECTIONS)
+	return l;
+      l = PREV_INSN (l);
+    }
+  gcc_unreachable ();
+}
+
+/* Return true if NOP needs to be inserted after 
+   NOTE_INSN_SWITCH_TEXT_SECTIONS.  This is the case when section starts with
+   EH landing pad. Otherwise the landing pad offset will end up being 0 which
+   will be interpreted as no landing pad and exceptions will not be delivered.
+ */
+
+bool
+maybe_add_nop_after_section_switch (void)
+{
+  if (!crtl->uses_eh_lsda
+      || !crtl->eh.call_site_record_v[1])
+    return false;
+  int n = vec_safe_length (crtl->eh.call_site_record_v[1]);
+  hash_set<rtx_insn *> visited;
+
+  for (int i = 0; i < n; ++i)
+    {
+      struct call_site_record_d *cs
+	 = (*crtl->eh.call_site_record_v[1])[i];
+      if (cs->landing_pad)
+	{
+	  rtx insn = first_in_partition (as_a <rtx_insn *> (cs->landing_pad),
+					 &visited);
+	  if (insn)
+	    {
+	      emit_insn_after (gen_nop (), insn);
+	      return true;
+	    }
+	}
+    }
+  return false;
+}
+
 static void
 dw2_output_call_site_table (int cs_format, int section)
 {
@@ -2749,8 +2803,10 @@ dw2_output_call_site_table (int cs_forma
       ASM_GENERATE_INTERNAL_LABEL (reg_end_lab, "LEHE", call_site_base + i);
 
       if (cs->landing_pad)
-	ASM_GENERATE_INTERNAL_LABEL (landing_pad_lab, "L",
-				     CODE_LABEL_NUMBER (cs->landing_pad));
+	{
+	  ASM_GENERATE_INTERNAL_LABEL (landing_pad_lab, "L",
+				       CODE_LABEL_NUMBER (cs->landing_pad));
+	}
 
       /* ??? Perhaps use insn length scaling if the assembler supports
 	 generic arithmetic.  */
Index: except.h
===================================================================
--- except.h	(revision 250312)
+++ except.h	(working copy)
@@ -283,6 +283,7 @@ extern eh_region get_eh_region_from_rtx
 extern eh_landing_pad get_eh_landing_pad_from_rtx (const_rtx);
 
 extern void finish_eh_generation (void);
+extern bool maybe_add_nop_after_section_switch (void);
 
 struct GTY(()) throw_stmt_node {
   gimple *stmt;
Index: final.c
===================================================================
--- final.c	(revision 250312)
+++ final.c	(working copy)
@@ -4581,6 +4582,7 @@ static unsigned int
 rest_of_handle_shorten_branches (void)
 {
   /* Shorten branches.  */
+  maybe_add_nop_after_section_switch ();
   shorten_branches (get_insns ());
   return 0;
 }