[PATCH] tree-optimization/44794 - avoid excessive RTL unrolling on epilogues

[PATCH] tree-optimization/44794 - avoid excessive RTL unrolling on epilogues

[Richard Biener]

The following adjusts tree_[transform_and_]unroll_loop to set an
upper bound on the number of iterations on the epilogue loop it
creates.  For the testcase at hand which involves array prefetching
this avoids applying RTL unrolling to them when -funroll-loops is
specified.

Other users of this API includes predictive commoning and
unroll-and-jam.

Bootstrapped and tested on x86_64-unknown-linux-gnu, queued for stage1.

	PR tree-optimization/44794
	* tree-ssa-loop-manip.cc (tree_transform_and_unroll_loop):
	If an epilogue loop is required set its iteration upper bound.
---
 gcc/tree-ssa-loop-manip.cc | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/gcc/tree-ssa-loop-manip.cc b/gcc/tree-ssa-loop-manip.cc
index 09acc1c94cc..c804a7353d5 100644
--- a/gcc/tree-ssa-loop-manip.cc
+++ b/gcc/tree-ssa-loop-manip.cc
@@ -1297,6 +1297,12 @@ tree_transform_and_unroll_loop (class loop *loop, unsigned factor,
 	}
 
       remove_path (exit);
+
+      /* The epilog loop latch executes at most factor - 1 times.
+	 Since the epilog is entered unconditionally it will need to handle
+	 up to factor executions of its body.  */
+      new_loop->any_upper_bound = 1;
+      new_loop->nb_iterations_upper_bound = factor - 1;
     }
   else
     new_exit = single_dom_exit (loop);
-- 
2.35.3