ifcvt.c (noce_get_alt_condition): If the condition is a compare against a constant...

* ifcvt.c (noce_get_alt_condition): If the condition is a compare
against a constant, try to adjust the compare to have the desired
constant in it so that min/max optimizations happen more often.

From-SVN: r44435

1 files changed, 109 insertions, 1 deletions

diff --git a/gcc/ifcvt.c b/gcc/ifcvt.c
index 08ec087..4de879d 100644
--- a/gcc/ifcvt.c
+++ b/gcc/ifcvt.c
@@ -1,5 +1,5 @@
 /* If-conversion support.
-   Copyright (C) 2000 Free Software Foundation, Inc.
+   Copyright (C) 2000, 2001 Free Software Foundation, Inc.
 
    This file is part of GNU CC.
 
@@ -1150,6 +1150,114 @@ noce_get_alt_condition (if_info, target, earliest)
     = GET_CODE (XEXP (SET_SRC (set), 2)) == LABEL_REF
       && XEXP (XEXP (SET_SRC (set), 2), 0) == JUMP_LABEL (if_info->jump);
 
+  /* If we're looking for a constant, try to make the conditional
+     have that constant in it.  There are two reasons why it may
+     not have the constant we want:
+
+     1. GCC may have needed to put the constant in a register, because
+        the target can't compare directly against that constant.  For
+        this case, we look for a SET immediately before the comparison
+        that puts a constant in that register.
+
+     2. GCC may have canonicalized the conditional, for example
+	replacing "if x < 4" with "if x <= 3".  We can undo that (or
+	make equivalent types of changes) to get the constants we need
+	if they're off by one in the right direction.  */
+
+  if (GET_CODE (target) == CONST_INT)
+    {
+      enum rtx_code code = GET_CODE (if_info->cond);
+      rtx op_a = XEXP (if_info->cond, 0);
+      rtx op_b = XEXP (if_info->cond, 1);
+      rtx prev_insn;
+
+      /* First, look to see if we put a constant in a register.  */
+      prev_insn = PREV_INSN (if_info->cond_earliest);
+      if (prev_insn
+	  && INSN_P (prev_insn)
+	  && GET_CODE (PATTERN (prev_insn)) == SET)
+	{
+	  rtx src = find_reg_equal_equiv_note (prev_insn);
+	  if (!src)
+	    src = SET_SRC (PATTERN (prev_insn));
+	  if (GET_CODE (src) == CONST_INT)
+	    {
+	      if (rtx_equal_p (op_a, SET_DEST (PATTERN (prev_insn))))
+		{
+		  op_a = src;
+		  if_info->cond_earliest = prev_insn;
+		}
+	      else if (rtx_equal_p (op_b, SET_DEST (PATTERN (prev_insn))))
+		{
+		  op_b = src;
+		  if_info->cond_earliest = prev_insn;
+		}
+
+	      if (GET_CODE (op_a) == CONST_INT)
+		{
+		  rtx tmp = op_a;
+		  op_a = op_b;
+		  op_b = tmp;
+		  code = swap_condition (code);
+		}
+	    }
+	}
+
+      /* Now, look to see if we can get the right constant by
+	 adjusting the conditional.  */
+      if (GET_CODE (op_b) == CONST_INT)
+	{
+	  HOST_WIDE_INT desired_val = INTVAL (target);
+	  HOST_WIDE_INT actual_val = INTVAL (op_b);
+
+	  switch (code)
+	    {
+	    case LT:
+	      if (actual_val == desired_val + 1)
+		{
+		  code = LE;
+		  op_b = GEN_INT (desired_val);
+		}
+	      break;
+	    case LE:
+	      if (actual_val == desired_val - 1)
+		{
+		  code = LT;
+		  op_b = GEN_INT (desired_val);
+		}
+	      break;
+	    case GT:
+	      if (actual_val == desired_val - 1)
+		{
+		  code = GE;
+		  op_b = GEN_INT (desired_val);
+		}
+	      break;
+	    case GE:
+	      if (actual_val == desired_val + 1)
+		{
+		  code = GT;
+		  op_b = GEN_INT (desired_val);
+		}
+	      break;
+	    default:
+	      break;
+	    }
+	}
+
+      /* If we made any changes, generate a new conditional that is
+	 equivalent to what we started with, but has the right
+	 constants in it.  */
+      if (code != GET_CODE (if_info->cond)
+	  || op_a != XEXP (if_info->cond, 0)
+	  || op_b != XEXP (if_info->cond, 1))
+	{
+	  cond = gen_rtx_fmt_ee (code, GET_MODE (cond), op_a, op_b);
+	  *earliest = if_info->cond_earliest;
+	  return cond;
+	}
+    }
+
   cond = canonicalize_condition (if_info->jump, cond, reverse,
 				 earliest, target);
   if (! cond || ! reg_mentioned_p (target, cond))