[PATCH] CSE if-converted loop bodies

[PATCH] CSE if-converted loop bodies

[Richard Biener]

if-conversion can leave us with quite a mess, esp. redundant loads.
This confuses vectorizer data-ref analysis enough to be worth
fixing.  So the following patch runs RPO VN on the loop body.
PR87746 contains some before/after dumps.

Now we only need to teach it some simple DSE...

Bootstrapped on x86_64-unknown-linux-gnu, testing in progress.

Richard.

2018-10-25  Richard Biener  <rguenther@suse.de>

	* tree-if-conv.c: Include tree-ssa-sccvn.h.
	(tree_if_conversion): Run CSE on the if-converted loop body.

diff --git a/gcc/tree-if-conv.c b/gcc/tree-if-conv.c
index 52aa5756c94..0ef7daa49e8 100644
--- a/gcc/tree-if-conv.c
+++ b/gcc/tree-if-conv.c
@@ -118,6 +118,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "cfganal.h"
 #include "internal-fn.h"
 #include "fold-const.h"
+#include "tree-ssa-sccvn.h"
 
 /* Only handle PHIs with no more arguments unless we are asked to by
    simd pragma.  */
@@ -2979,6 +2980,7 @@ tree_if_conversion (struct loop *loop)
   unsigned int todo = 0;
   bool aggressive_if_conv;
   struct loop *rloop;
+  bitmap exit_bbs;
 
  again:
   rloop = NULL;
@@ -3056,6 +3058,14 @@ tree_if_conversion (struct loop *loop)
   /* Delete dead predicate computations.  */
   ifcvt_local_dce (loop->header);
 
+  /* Perform local CSE, this esp. helps the vectorizer analysis if loads
+     and stores are involved.
+     ???  We'll still keep dead stores though.  */
+  exit_bbs = BITMAP_ALLOC (NULL);
+  bitmap_set_bit (exit_bbs, single_exit (loop)->dest->index);
+  todo |= do_rpo_vn (cfun, loop_preheader_edge (loop), exit_bbs);
+  BITMAP_FREE (exit_bbs);
+
   todo |= TODO_cleanup_cfg;
 
  cleanup: