re PR rtl-optimization/64616 (Redundant ldr when accessing var inside and outside a loop)

2015-05-13  Thomas Preud'homme  <thomas.preudhomme@arm.com>

    gcc/
    PR rtl-optimization/64616
    * loop-invariant.c (can_move_invariant_reg): New.
    (move_invariant_reg): Call above new function to decide whether
    instruction can just be moved, skipping creation of temporary
    register.

    gcc/testsuite/
    PR rtl-optimization/64616
    * gcc.dg/loop-8.c: New test.
    * gcc.dg/loop-9.c: New test.

From-SVN: r223113

gcc/ChangeLog

@@ -1,3 +1,11 @@
+2015-05-13  Thomas Preud'homme  <thomas.preudhomme@arm.com>
+
+	PR rtl-optimization/64616
+	* loop-invariant.c (can_move_invariant_reg): New.
+	(move_invariant_reg): Call above new function to decide whether
+	instruction can just be moved, skipping creation of temporary
+	register.
+
 2015-05-12  Jan Hubicka  <hubicka@ucw.cz>
 
 	PR target/pr66047.c

gcc/loop-invariant.c

@@ -1511,6 +1511,79 @@ replace_uses (struct invariant *inv, rtx reg, bool in_group)
   return 1;
 }
 
+/* Whether invariant INV setting REG can be moved out of LOOP, at the end of
+   the block preceding its header.  */
+
+static bool
+can_move_invariant_reg (struct loop *loop, struct invariant *inv, rtx reg)
+{
+  df_ref def, use;
+  unsigned int dest_regno, defs_in_loop_count = 0;
+  rtx_insn *insn = inv->insn;
+  basic_block bb = BLOCK_FOR_INSN (inv->insn);
+
+  /* We ignore hard register and memory access for cost and complexity reasons.
+     Hard register are few at this stage and expensive to consider as they
+     require building a separate data flow.  Memory access would require using
+     df_simulate_* and can_move_insns_across functions and is more complex.  */
+  if (!REG_P (reg) || HARD_REGISTER_P (reg))
+    return false;
+
+  /* Check whether the set is always executed.  We could omit this condition if
+     we know that the register is unused outside of the loop, but it does not
+     seem worth finding out.  */
+  if (!inv->always_executed)
+    return false;
+
+  /* Check that all uses that would be dominated by def are already dominated
+     by it.  */
+  dest_regno = REGNO (reg);
+  for (use = DF_REG_USE_CHAIN (dest_regno); use; use = DF_REF_NEXT_REG (use))
+    {
+      rtx_insn *use_insn;
+      basic_block use_bb;
+
+      use_insn = DF_REF_INSN (use);
+      use_bb = BLOCK_FOR_INSN (use_insn);
+
+      /* Ignore instruction considered for moving.  */
+      if (use_insn == insn)
+	continue;
+
+      /* Don't consider uses outside loop.  */
+      if (!flow_bb_inside_loop_p (loop, use_bb))
+	continue;
+
+      /* Don't move if a use is not dominated by def in insn.  */
+      if (use_bb == bb && DF_INSN_LUID (insn) >= DF_INSN_LUID (use_insn))
+	return false;
+      if (!dominated_by_p (CDI_DOMINATORS, use_bb, bb))
+	return false;
+    }
+
+  /* Check for other defs.  Any other def in the loop might reach a use
+     currently reached by the def in insn.  */
+  for (def = DF_REG_DEF_CHAIN (dest_regno); def; def = DF_REF_NEXT_REG (def))
+    {
+      basic_block def_bb = DF_REF_BB (def);
+
+      /* Defs in exit block cannot reach a use they weren't already.  */
+      if (single_succ_p (def_bb))
+	{
+	  basic_block def_bb_succ;
+
+	  def_bb_succ = single_succ (def_bb);
+	  if (!flow_bb_inside_loop_p (loop, def_bb_succ))
+	    continue;
+	}
+
+      if (++defs_in_loop_count > 1)
+	return false;
+    }
+
+  return true;
+}
+
 /* Move invariant INVNO out of the LOOP.  Returns true if this succeeds, false
    otherwise.  */
 
@@ -1544,11 +1617,8 @@ move_invariant_reg (struct loop *loop, unsigned invno)
 	    }
 	}
 
-      /* Move the set out of the loop.  If the set is always executed (we could
-	 omit this condition if we know that the register is unused outside of
-	 the loop, but it does not seem worth finding out) and it has no uses
-	 that would not be dominated by it, we may just move it (TODO).
-	 Otherwise we need to create a temporary register.  */
+      /* If possible, just move the set out of the loop.  Otherwise, we
+	 need to create a temporary register.  */
       set = single_set (inv->insn);
       reg = dest = SET_DEST (set);
       if (GET_CODE (reg) == SUBREG)
@@ -1556,19 +1626,25 @@ move_invariant_reg (struct loop *loop, unsigned invno)
       if (REG_P (reg))
 	regno = REGNO (reg);
 
-      reg = gen_reg_rtx_and_attrs (dest);
+      if (!can_move_invariant_reg (loop, inv, reg))
+	{
+	  reg = gen_reg_rtx_and_attrs (dest);
 
-      /* Try replacing the destination by a new pseudoregister.  */
-      validate_change (inv->insn, &SET_DEST (set), reg, true);
+	  /* Try replacing the destination by a new pseudoregister.  */
+	  validate_change (inv->insn, &SET_DEST (set), reg, true);
 
-      /* As well as all the dominated uses.  */
-      replace_uses (inv, reg, true);
+	  /* As well as all the dominated uses.  */
+	  replace_uses (inv, reg, true);
 
-      /* And validate all the changes.  */
-      if (!apply_change_group ())
-	goto fail;
+	  /* And validate all the changes.  */
+	  if (!apply_change_group ())
+	    goto fail;
 
-      emit_insn_after (gen_move_insn (dest, reg), inv->insn);
+	  emit_insn_after (gen_move_insn (dest, reg), inv->insn);
+	}
+      else if (dump_file)
+	fprintf (dump_file, "Invariant %d moved without introducing a new "
+			    "temporary register\n", invno);
       reorder_insns (inv->insn, inv->insn, BB_END (preheader));
 
       /* If there is a REG_EQUAL note on the insn we just moved, and the

gcc/testsuite/ChangeLog

@@ -1,3 +1,9 @@
+2015-05-13  Thomas Preud'homme  <thomas.preudhomme@arm.com>
+
+	PR rtl-optimization/64616
+	* gcc.dg/loop-8.c: New test.
+	* gcc.dg/loop-9.c: New test.
+
 2015-05-12  Jan Hubicka  <hubicka@ucw.cz>
 
 	PR target/pr66047.c

gcc/testsuite/gcc.dg/loop-8.c

@@ -0,0 +1,24 @@
+/* { dg-do compile } */
+/* { dg-options "-O1 -fdump-rtl-loop2_invariant" } */
+
+void
+f (int *a, int *b)
+{
+  int i;
+
+  for (i = 0; i < 100; i++)
+    {
+      int d = 42;
+
+      a[i] = d;
+      if (i % 2)
+	d = i;
+      b[i] = d;
+    }
+}
+
+/* Load of 42 is moved out of the loop, introducing a new pseudo register.  */
+/* { dg-final { scan-rtl-dump-times "Decided" 1 "loop2_invariant" } } */
+/* { dg-final { scan-rtl-dump-not "without introducing a new temporary register" "loop2_invariant" } } */
+/* { dg-final { cleanup-rtl-dump "loop2_invariant" } } */
+

gcc/testsuite/gcc.dg/loop-9.c

@@ -0,0 +1,16 @@
+/* { dg-do compile } */
+/* { dg-options "-O1 -fdump-rtl-loop2_invariant" } */
+
+void
+f (double *a)
+{
+  int i;
+  for (i = 0; i < 100; i++)
+    a[i] = 18.4242;
+}
+
+/* Load of x is moved out of the loop.  */
+/* { dg-final { scan-rtl-dump "Decided" "loop2_invariant" } } */
+/* { dg-final { scan-rtl-dump "without introducing a new temporary register" "loop2_invariant" } } */
+/* { dg-final { cleanup-rtl-dump "loop2_invariant" } } */
+