[RTL ifcvt] Transform (X == CST) ? -CST : Y into (X == CST) ? -X : Y when conditional negation is available

        * ifcvt.c (noce_try_avoid_const_materialization): New function.
        (noce_process_if_block): Use it.

        * gcc.target/aarch64/ifcvt_avoid_const_materialization_1.c: New test.

From-SVN: r240649

1 files changed, 80 insertions, 0 deletions

diff --git a/gcc/ifcvt.c b/gcc/ifcvt.c
index 24542f0..203cfe9 100644
--- a/gcc/ifcvt.c
+++ b/gcc/ifcvt.c
@@ -1313,6 +1313,84 @@ noce_try_inverse_constants (struct noce_if_info *if_info)
   return false;
 }
 
+/* Try to avoid materializing a constant if we know it's in one of the
+   registers.  For example:
+   (X == CST) ? -CST : Y --> (X == CST) ? -X : Y.
+   Do this only if conditional negation is available.
+   Similar for bitwise NOT.  */
+
+static bool
+noce_try_avoid_const_materialization (struct noce_if_info *if_info)
+{
+  if (!noce_simple_bbs (if_info))
+    return false;
+
+  rtx cond = if_info->cond;
+  rtx a = if_info->a;
+  rtx b = if_info->b;
+  rtx_code code = GET_CODE (cond);
+  machine_mode mode = GET_MODE (if_info->x);
+
+  if (!(code == EQ || code == NE)
+      || !REG_P (XEXP (cond, 0))
+      || !REG_P (if_info->x)
+      || GET_MODE (XEXP (cond, 0)) != mode
+      || !CONST_INT_P (XEXP (cond, 1)))
+    return false;
+
+  rtx cst = XEXP (cond, 1);
+  if (cst == CONST0_RTX (mode))
+    return false;
+
+  rtx non_cst = XEXP (cond, 0);
+  rtx eq_side = code == EQ ? b : a;
+  if (!CONST_INT_P (eq_side))
+    return false;
+
+  HOST_WIDE_INT cstval = INTVAL (cst);
+  HOST_WIDE_INT eq_side_val = INTVAL (eq_side);
+
+  rtx_code op_code;
+  if (eq_side_val == ~cstval)
+    op_code = NOT;
+  else if (eq_side_val != HOST_WIDE_INT_MIN && (cstval == -eq_side_val))
+    op_code = NEG;
+  else
+    return false;
+
+  /* By the rules of the negcc/notcc optabs must happen when the COND is true,
+     in this case when register in COND is equal to CST so always set the
+     comparison to EQ.  */
+  if (code == NE)
+    {
+      a = non_cst;
+      cond = gen_rtx_fmt_ee (EQ, GET_MODE (cond), non_cst, cst);
+    }
+  else
+    b = non_cst;
+
+  start_sequence ();
+  rtx target
+    = emit_conditional_neg_or_complement (if_info->x, op_code, mode,
+					   cond, a, b);
+  if (!target)
+    {
+      end_sequence ();
+      return false;
+    }
+
+  if (target != if_info->x)
+    noce_emit_move_insn (if_info->x, target);
+
+  rtx_insn *seq = end_ifcvt_sequence (if_info);
+  if (!seq)
+    return false;
+
+   emit_insn_before_setloc (seq, if_info->jump,
+			     INSN_LOCATION (if_info->insn_a));
+  if_info->transform_name = "noce_try_avoid_const_materialization";
+  return true;
+}
 
 /* Convert "if (test) x = a; else x = b", for A and B constant.
    Also allow A = y + c1, B = y + c2, with a common y between A
@@ -3606,6 +3684,8 @@ noce_process_if_block (struct noce_if_info *if_info)
     goto success;
   if (noce_try_inverse_constants (if_info))
     goto success;
+  if (noce_try_avoid_const_materialization (if_info))
+    goto success;
   if (!targetm.have_conditional_execution ()
       && noce_try_store_flag_constants (if_info))
     goto success;