rs6000-p8swap.c (swap_feeds_both_load_and_store): New function.

2018-01-02  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>

	* config/rs6000/rs6000-p8swap.c (swap_feeds_both_load_and_store):
	New function.
	(rs6000_analyze_swaps): Mark a web unoptimizable if it contains a
	swap associated with both a load and a store.

From-SVN: r256111

gcc/ChangeLog

+2018-01-02  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>
+
+	* config/rs6000/rs6000-p8swap.c (swap_feeds_both_load_and_store):
+	New function.
+	(rs6000_analyze_swaps): Mark a web unoptimizable if it contains a
+	swap associated with both a load and a store.
+
 2018-01-02  Andrew Waterman  <andrew@sifive.com>
 
 	* config/riscv/linux.h (ICACHE_FLUSH_FUNC): New.

gcc/config/rs6000/rs6000-p8swap.c

@@ -328,6 +328,38 @@ insn_is_swap_p (rtx insn)
   return 1;
 }
 
+/* Return 1 iff UID, known to reference a swap, is both fed by a load
+   and a feeder of a store.  */
+static unsigned int
+swap_feeds_both_load_and_store (swap_web_entry *insn_entry)
+{
+  rtx insn = insn_entry->insn;
+  struct df_insn_info *insn_info = DF_INSN_INFO_GET (insn);
+  df_ref def, use;
+  struct df_link *link = 0;
+  rtx_insn *load = 0, *store = 0;
+  bool fed_by_load = 0;
+  bool feeds_store = 0;
+
+  FOR_EACH_INSN_INFO_USE (use, insn_info)
+    {
+      link = DF_REF_CHAIN (use);
+      load = DF_REF_INSN (link->ref);
+      if (insn_is_load_p (load) && insn_is_swap_p (load))
+	fed_by_load = 1;
+    }
+
+  FOR_EACH_INSN_INFO_DEF (def, insn_info)
+    {
+      link = DF_REF_CHAIN (def);
+      store = DF_REF_INSN (link->ref);
+      if (insn_is_store_p (store) && insn_is_swap_p (store))
+	feeds_store = 1;
+    }
+
+  return fed_by_load && feeds_store;
+}
+
 /* Return TRUE if insn is a swap fed by a load from the constant pool.  */
 static bool
 const_load_sequence_p (swap_web_entry *insn_entry, rtx insn)
@@ -2030,6 +2062,14 @@ rs6000_analyze_swaps (function *fun)
 	  && !insn_entry[i].is_swap && !insn_entry[i].is_swappable)
 	root->web_not_optimizable = 1;
 
+      /* If we have a swap that is both fed by a permuting load
+	 and a feeder of a permuting store, then the optimization
+	 isn't appropriate.  (Consider vec_xl followed by vec_xst_be.)  */
+      else if (insn_entry[i].is_swap && !insn_entry[i].is_load
+	       && !insn_entry[i].is_store
+	       && swap_feeds_both_load_and_store (&insn_entry[i]))
+	root->web_not_optimizable = 1;
+
       /* If we have permuting loads or stores that are not accompanied
 	 by a register swap, the optimization isn't appropriate.  */
       else if (insn_entry[i].is_load && insn_entry[i].is_swap)