[gcc r12-5150] Resolve entry loop condition for the edge remaining in the loop.

[gcc r12-5150] Resolve entry loop condition for the edge remaining in the loop.

[Aldy Hernandez]

https://gcc.gnu.org/g:3e5a19053310ad090b930fbecebceb28bd1b91a4

commit r12-5150-g3e5a19053310ad090b930fbecebceb28bd1b91a4
Author: Aldy Hernandez <aldyh@redhat.com>
Date:   Thu Nov 11 11:27:07 2021 +0100

    Resolve entry loop condition for the edge remaining in the loop.
    
    There is a known failure for gfortran.dg/vector_subscript_1.f90.  It
    was previously failing for all optimization levels except -Os.
    Getting the loop header copying right, now makes it fail for all
    levels :-).
    
    Tested on x86-64 Linux.
    
    Co-authored-by: Richard Biener <rguenther@suse.de>
    
    gcc/ChangeLog:
    
            * tree-ssa-loop-ch.c (entry_loop_condition_is_static): Resolve
            statically to the edge remaining in the loop.

Diff:
---
 gcc/tree-ssa-loop-ch.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/gcc/tree-ssa-loop-ch.c b/gcc/tree-ssa-loop-ch.c
index c7d86d751d4..af3401f112c 100644
--- a/gcc/tree-ssa-loop-ch.c
+++ b/gcc/tree-ssa-loop-ch.c
@@ -57,10 +57,24 @@ entry_loop_condition_is_static (class loop *l, path_range_query *query)
       || !irange::supports_type_p (TREE_TYPE (gimple_cond_lhs (last))))
     return false;
 
+  edge true_e, false_e;
+  extract_true_false_edges_from_block (e->dest, &true_e, &false_e);
+
+  /* If neither edge is the exit edge, this is not a case we'd like to
+     special-case.  */
+  if (!loop_exit_edge_p (l, true_e) && !loop_exit_edge_p (l, false_e))
+    return false;
+
+  tree desired_static_value;
+  if (loop_exit_edge_p (l, true_e))
+    desired_static_value = boolean_false_node;
+  else
+    desired_static_value = boolean_true_node;
+
   int_range<2> r;
   query->compute_ranges (e);
   query->range_of_stmt (r, last);
-  return r == int_range<2> (boolean_true_node, boolean_true_node);
+  return r == int_range<2> (desired_static_value, desired_static_value);
 }
 
 /* Check whether we should duplicate HEADER of LOOP.  At most *LIMIT