Another fix for single-element permutes (PR 84265)

[Richard Sandiford]

PR83753 was about a case in which we ended up trying to "vectorise"
a group of loads ore stores using single-element vectors.  The problem
was that we were classifying the load or store as VMAT_CONTIGUOUS_PERMUTE
rather than VMAT_CONTIGUOUS, even though it doesn't make sense to permute
a single-element vector.

In that PR it was enough to change get_group_load_store_type,
because vectorisation ended up being unprofitable and so we didn't
take things further.  But when vectorisation is profitable, the same
fix is needed in vectorizable_load and vectorizable_store.

Tested on aarch64-linux-gnu, aarch64_be-elf and x86_64-linux-gnu.
OK to install?

Richard


2018-02-08  Richard Sandiford  <richard.sandif...@linaro.org>

gcc/
        PR tree-optimization/84265
        * tree-vect-stmts.c (vectorizable_store): Don't treat
        VMAT_CONTIGUOUS accesses as grouped.
        (vectorizable_load): Likewise.

gcc/testsuite/
        PR tree-optimization/84265
        * gcc.dg/vect/pr84265.c: New test.

Index: gcc/tree-vect-stmts.c
===================================================================
--- gcc/tree-vect-stmts.c       2018-01-30 09:45:27.710764075 +0000
+++ gcc/tree-vect-stmts.c       2018-02-08 13:26:39.242566948 +0000
@@ -6214,7 +6214,8 @@ vectorizable_store (gimple *stmt, gimple
     }
 
   grouped_store = (STMT_VINFO_GROUPED_ACCESS (stmt_info)
-                  && memory_access_type != VMAT_GATHER_SCATTER);
+                  && memory_access_type != VMAT_GATHER_SCATTER
+                  && (slp || memory_access_type != VMAT_CONTIGUOUS));
   if (grouped_store)
     {
       first_stmt = GROUP_FIRST_ELEMENT (stmt_info);
@@ -7696,7 +7697,8 @@ vectorizable_load (gimple *stmt, gimple_
       return true;
     }
 
-  if (memory_access_type == VMAT_GATHER_SCATTER)
+  if (memory_access_type == VMAT_GATHER_SCATTER
+      || (!slp && memory_access_type == VMAT_CONTIGUOUS))
     grouped_load = false;
 
   if (grouped_load)
Index: gcc/testsuite/gcc.dg/vect/pr84265.c
===================================================================
--- /dev/null   2018-02-08 11:17:10.862716283 +0000
+++ gcc/testsuite/gcc.dg/vect/pr84265.c 2018-02-08 13:26:39.240567025 +0000
@@ -0,0 +1,23 @@
+/* { dg-do compile } */
+
+struct a
+{
+  unsigned long b;
+  unsigned long c;
+  int d;
+  int *e;
+  char f;
+};
+
+struct
+{
+  int g;
+  struct a h[];
+} i;
+
+int j, k;
+void l ()
+{
+  for (; k; k++)
+    j += (int) (i.h[k].c - i.h[k].b);
+}