[PATCH] if-conv: Delete dead stmts backwards in ifcvt_local_dce [PR94283]

[Jakub Jelinek via Gcc-patches]

On Tue, Mar 24, 2020 at 10:59:19AM +0100, Richard Biener wrote:
> Likely
> 
>   /* Delete dead statements.  */
>   gsi = gsi_start_bb (bb);
>   while (!gsi_end_p (gsi))
>     {
> 
> needs to instead work back-to-front for debug stmt adjustment to work

Indeed, that seems to work.  Ok for trunk if it passes bootstrap/regtest?

2020-03-24  Richard Biener  <rguent...@suse.de>
            Jakub Jelinek  <ja...@redhat.com>

        PR debug/94283
        * tree-if-conv.c (ifcvt_local_dce): Delete dead statements backwards.

        * gcc.dg/pr94283.c: New test.

--- gcc/tree-if-conv.c.jj       2020-03-24 09:34:35.152087914 +0100
+++ gcc/tree-if-conv.c  2020-03-24 11:13:41.179903247 +0100
@@ -2973,9 +2973,11 @@ ifcvt_local_dce (class loop *loop)
        }
     }
   /* Delete dead statements.  */
-  gsi = gsi_start_bb (bb);
+  gsi = gsi_last_bb (bb);
   while (!gsi_end_p (gsi))
     {
+      gimple_stmt_iterator gsiprev = gsi;
+      gsi_prev (&gsiprev);
       stmt = gsi_stmt (gsi);
       if (gimple_store_p (stmt))
        {
@@ -2986,14 +2988,13 @@ ifcvt_local_dce (class loop *loop)
          if (dse_classify_store (&write, stmt, false, NULL, NULL, latch_vdef)
              == DSE_STORE_DEAD)
            delete_dead_or_redundant_assignment (&gsi, "dead");
-         else
-           gsi_next (&gsi);
+         gsi = gsiprev;
          continue;
        }
 
       if (gimple_plf (stmt, GF_PLF_2))
        {
-         gsi_next (&gsi);
+         gsi = gsiprev;
          continue;
        }
       if (dump_file && (dump_flags & TDF_DETAILS))
@@ -3003,6 +3004,7 @@ ifcvt_local_dce (class loop *loop)
        }
       gsi_remove (&gsi, true);
       release_defs (stmt);
+      gsi = gsiprev;
     }
 }
 
--- gcc/testsuite/gcc.dg/pr94283.c.jj   2020-03-24 11:15:35.782163250 +0100
+++ gcc/testsuite/gcc.dg/pr94283.c      2020-03-24 11:16:37.909219978 +0100
@@ -0,0 +1,16 @@
+/* PR debug/94283 */
+/* { dg-do compile } */
+/* { dg-options "-O3 -fno-tree-dce -fcompare-debug" } */
+
+void
+foo (int *n)
+{
+  for (int i = 0; i < 32; i++)
+    {
+      int x = 0;
+      x++;
+      if (i & 4)
+       x++;
+      x++;
+    }
+}


        Jakub