[gcc r12-4905] path solver: Prefer range_of_expr instead of range_on_edge.

[Aldy Hernandez <aldyh@gcc.gnu.org>]

https://gcc.gnu.org/g:6a9678f0b30d36ae13259ad635e175a1e24917a1

commit r12-4905-g6a9678f0b30d36ae13259ad635e175a1e24917a1
Author: Aldy Hernandez <aldyh@redhat.com>
Date:   Thu Nov 4 12:37:16 2021 +0100

    path solver: Prefer range_of_expr instead of range_on_edge.
    
    The range_of_expr method provides better caching than range_on_edge.
    If we have a statement, we can just it and avoid the range_on_edge
    dance.  Plus we can use all the range_of_expr fanciness.
    
    Tested on x86-64 and ppc64le Linux with the usual regstrap.  I also
    verified that the before and after number of threads was the same or
    greater in a suite of .ii files from a bootstrap.
    
    gcc/ChangeLog:
    
            PR tree-optimization/102943
            * gimple-range-path.cc (path_range_query::range_on_path_entry):
            Prefer range_of_expr unless there are no statements in the BB.

Diff:
---
 gcc/gimple-range-path.cc | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/gcc/gimple-range-path.cc b/gcc/gimple-range-path.cc
index 42309886c94..9175651e896 100644
--- a/gcc/gimple-range-path.cc
+++ b/gcc/gimple-range-path.cc
@@ -135,10 +135,24 @@ void
 path_range_query::range_on_path_entry (irange &r, tree name)
 {
   gcc_checking_assert (defined_outside_path (name));
-  int_range_max tmp;
   basic_block entry = entry_bb ();
-  bool changed = false;
 
+  // Prefer to use range_of_expr if we have a statement to look at,
+  // since it has better caching than range_on_edge.
+  gimple *last = last_stmt (entry);
+  if (last)
+    {
+      if (m_ranger.range_of_expr (r, name, last))
+	return;
+      gcc_unreachable ();
+    }
+
+  // If we have no statement, look at all the incoming ranges to the
+  // block.  This can happen when we're querying a block with only an
+  // outgoing edge (no statement but the fall through edge), but for
+  // which we can determine a range on entry to the block.
+  int_range_max tmp;
+  bool changed = false;
   r.set_undefined ();
   for (unsigned i = 0; i < EDGE_COUNT (entry->preds); ++i)
     {