[committed] [PR tree-optimization/91090] Fix logic error in jump threading

[Jeff Law]

This code was copied and reindented from tree-vrp.c.  It looks like in
that process the second conditional moved inside the true arm of the
first conditional, which was wrong.

It won't cause incorrect code, just missed optimizations.  I also
verified that the code is still live -- it triggers during a bootstrap
when building the Fortran front-end for example.  Given that I just
fixed it on the trunk.  I don't think there's much value in fixing on
the release branches.

Bootstrapped and regression tested on x86_64-linux-gnu.

Installed on the trunk.

jeff

commit f60e7cee5700a9f9515ab4e2a922c325149c49e1
Author: law <law@138bc75d-0d04-0410-961f-82ee72b054a4>
Date:   Sun Jul 7 18:42:45 2019 +0000

            PR tree-optimization/91090
            * tree-ssa-dom.c (simplify_stmt_for_jump_threading): Fix logic error
            in handling of ranges to simplify switch statements.
    
    git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@273184 
138bc75d-0d04-0410-961f-82ee72b054a4

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 0ef7eb6b93b..9f83f75b0bf 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2019-07-07  Jeff Law  <l...@redhat.com>
+
+       PR tree-optimization/91090
+       * tree-ssa-dom.c (simplify_stmt_for_jump_threading): Fix logic error
+       in handling of ranges to simplify switch statements.
+
 2019-07-07  Iain Sandoe  <i...@sandoe.co.uk>
 
        * config/darwin.c (darwin_override_options): Make a final check on PIC
diff --git a/gcc/tree-ssa-dom.c b/gcc/tree-ssa-dom.c
index b0d56fcf3e3..17c852d5299 100644
--- a/gcc/tree-ssa-dom.c
+++ b/gcc/tree-ssa-dom.c
@@ -913,21 +913,26 @@ simplify_stmt_for_jump_threading (gimple *stmt,
 
          find_case_label_range (switch_stmt, vr->min (), vr->max (), &i, &j);
 
+         /* Is there only one such label?  */
          if (i == j)
            {
              tree label = gimple_switch_label (switch_stmt, i);
              tree singleton;
 
+             /* The i'th label will only be taken if the value range of the
+                operand is entirely within the bounds of this label.  */
              if (CASE_HIGH (label) != NULL_TREE
                  ? (tree_int_cst_compare (CASE_LOW (label), vr->min ()) <= 0
                     && tree_int_cst_compare (CASE_HIGH (label), vr->max ()) >= 
0)
                  : (vr->singleton_p (&singleton)
                     && tree_int_cst_equal (CASE_LOW (label), singleton)))
                return label;
-
-             if (i > j)
-               return gimple_switch_label (switch_stmt, 0);
            }
+
+         /* If there are no such labels, then the default label
+            will be taken.  */
+         if (i > j)
+           return gimple_switch_label (switch_stmt, 0);
        }
 
       if (vr->kind () == VR_ANTI_RANGE)