Fix PR middle-end/102764

[Eric Botcazou via Gcc-patches]

This is a regression present on the mainline in the form of a -fcompare-debug 
failure at -O3 on a compiler-generated testcase.  Fixed by disregarding a 
debug statement in the last position of a basic block to reset the current 
location for the outgoing edges.

Bootstrapped/regtested on x86-64/Linux, applied on the mainline as obvious.


2021-10-20  Eric Botcazou  <ebotca...@adacore.com>

        PR middle-end/102764
        * cfgexpand.c (expand_gimple_basic_block): Disregard a final debug
        statement to reset the current location for the outgoing edges.


2021-10-20  Eric Botcazou  <ebotca...@adacore.com>

        * gcc.dg/pr102764.c: New test.

-- 
Eric Botcazou
diff --git a/gcc/cfgexpand.c b/gcc/cfgexpand.c
index 03260b019e5..8b067f9d848 100644
--- a/gcc/cfgexpand.c
+++ b/gcc/cfgexpand.c
@@ -6090,7 +6090,7 @@ expand_gimple_basic_block (basic_block bb, bool disable_tail_calls)
   /* Expand implicit goto and convert goto_locus.  */
   FOR_EACH_EDGE (e, ei, bb->succs)
     {
-      if (e->goto_locus != UNKNOWN_LOCATION || !stmt)
+      if (e->goto_locus != UNKNOWN_LOCATION || !stmt || is_gimple_debug (stmt))
 	set_curr_insn_location (e->goto_locus);
       if ((e->flags & EDGE_FALLTHRU) && e->dest != bb->next_bb)
 	{

/* PR middle-end/102764 */
/* Reported by Chengnian Sun <cn...@uwaterloo.ca> */

/* { dg-do compile } */
/* { dg-options "-O3 -fcompare-debug" } */

volatile int a;

void main (void)
{
  for (int i = 0; i < 1000; i++)
    if (i % 17)
      a++;
}