middle-end: Add an RPO pass after successful vectorization

Following my current SVE predicate optimization series a problem has presented
itself in that the way vector masks are generated for masked operations relies
on CSE to share masks efficiently.

The issue however is that masking is done using the & operand and & is
associative and so reassoc decides to reassociate the masked operations.

This makes CSE then unable to CSE an unmasked and a masked operation leading to
duplicate operations being performed.

To counter this we want to add an RPO pass over the vectorized loop body when
vectorization succeeds.  This makes it then no longer reliant on the RTL level
CSE.

I have not added a testcase for this as it requires the changes in my patch
series, however the entire series relies on this patch to work so all the
tests there cover it.

gcc/ChangeLog:

	* tree-vectorizer.c (vectorize_loops): Do local CSE through RPVN upon
	successful vectorization.

diff --git a/gcc/tree-vectorizer.c b/gcc/tree-vectorizer.c
index 71f12b3257e69a033eb23fe4fe05f8c342a290d8..3247c9af23b3854efb0d902c738a54e6883ff4b0 100644 (file)
--- a/gcc/tree-vectorizer.c
+++ b/gcc/tree-vectorizer.c
@@ -81,7 +81,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "gimple-pretty-print.h"
 #include "opt-problem.h"
 #include "internal-fn.h"
-
+#include "tree-ssa-sccvn.h"
 
 /* Loop or bb location, with hotness information.  */
 dump_user_location_t vect_location;
@@ -1276,23 +1276,6 @@ vectorize_loops (void)
          }
       }
 
-  for (i = 1; i < number_of_loops (cfun); i++)
-    {
-      loop_vec_info loop_vinfo;
-      bool has_mask_store;
-
-      loop = get_loop (cfun, i);
-      if (!loop || !loop->aux)
-       continue;
-      loop_vinfo = (loop_vec_info) loop->aux;
-      has_mask_store = LOOP_VINFO_HAS_MASK_STORE (loop_vinfo);
-      delete loop_vinfo;
-      if (has_mask_store
-         && targetm.vectorize.empty_mask_is_expensive (IFN_MASK_STORE))
-       optimize_mask_stores (loop);
-      loop->aux = NULL;
-    }
-
   /* Fold IFN_GOMP_SIMD_{VF,LANE,LAST_LANE,ORDERED_{START,END}} builtins.  */
   if (cfun->has_simduid_loops)
     {
@@ -1300,14 +1283,12 @@ vectorize_loops (void)
       /* Avoid stale SCEV cache entries for the SIMD_LANE defs.  */
       scev_reset ();
     }
-
   /* Shrink any "omp array simd" temporary arrays to the
      actual vectorization factors.  */
   if (simd_array_to_simduid_htab)
     shrink_simd_arrays (simd_array_to_simduid_htab, simduid_to_vf_htab);
   delete simduid_to_vf_htab;
   cfun->has_simduid_loops = false;
-  vect_slp_fini ();
 
   if (num_vectorized_loops > 0)
     {
@@ -1315,9 +1296,39 @@ vectorize_loops (void)
         ???  Also while we try hard to update loop-closed SSA form we fail
         to properly do this in some corner-cases (see PR56286).  */
       rewrite_into_loop_closed_ssa (NULL, TODO_update_ssa_only_virtuals);
-      return TODO_cleanup_cfg;
+      ret |= TODO_cleanup_cfg;
     }
 
+  for (i = 1; i < number_of_loops (cfun); i++)
+    {
+      loop_vec_info loop_vinfo;
+      bool has_mask_store;
+
+      loop = get_loop (cfun, i);
+      if (!loop || !loop->aux)
+       continue;
+      loop_vinfo = (loop_vec_info) loop->aux;
+      has_mask_store = LOOP_VINFO_HAS_MASK_STORE (loop_vinfo);
+      delete loop_vinfo;
+      if (has_mask_store
+         && targetm.vectorize.empty_mask_is_expensive (IFN_MASK_STORE))
+       optimize_mask_stores (loop);
+
+      auto_bitmap exit_bbs;
+      /* Perform local CSE, this esp. helps because we emit code for
+        predicates that need to be shared for optimal predicate usage.
+        However reassoc will re-order them and prevent CSE from working
+        as it should.  CSE only the loop body, not the entry.  */
+      bitmap_set_bit (exit_bbs, single_exit (loop)->dest->index);
+
+      edge entry = EDGE_PRED (loop_preheader_edge (loop)->src, 0);
+      do_rpo_vn (cfun, entry, exit_bbs);
+
+      loop->aux = NULL;
+    }
+
+  vect_slp_fini ();
+
   return ret;
 }