Patchwork Canonicalize compares in combine [1/3] Abstract out parts of simplify_comparison()

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Submitter Chung-Lin Tang
Date April 22, 2011, 3:21 p.m.
Message ID <4DB19CF4.2010108@codesourcery.com>
Download mbox | patch
Permalink /patch/92543/
State New
Headers show

Comments

Chung-Lin Tang - April 22, 2011, 3:21 p.m.
This patch abstracts out a small part of simplify_comparison(), into a
new function simplify_compare_const(). The parts are basically where the
comparison RTX code and a constant operand (op1) can be simplified
towards "compare with zero". Note this part leaves op0 untouched, thus
not passed into simplify_compare_const() by reference.

By itself this patch should only be a code reorganization, and changes
nothing to the compiler.

This is part of a small improvement to the compare combining code in the
later patch. During before, the entire case required operand[1] of i3 to
be const0_rtx, now we can try a little tweaking of the code and
constant, and see if it then changes to a cmp zero.

This abstracted patch was bootstrapped and tested independently on i686,
to be sure it was only a reorg.
Jeff Law - April 25, 2011, 5:10 p.m.
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Hash: SHA1

On 04/22/11 09:21, Chung-Lin Tang wrote:
> This patch abstracts out a small part of simplify_comparison(), into a
> new function simplify_compare_const(). The parts are basically where the
> comparison RTX code and a constant operand (op1) can be simplified
> towards "compare with zero". Note this part leaves op0 untouched, thus
> not passed into simplify_compare_const() by reference.
> 
> By itself this patch should only be a code reorganization, and changes
> nothing to the compiler.
> 
> This is part of a small improvement to the compare combining code in the
> later patch. During before, the entire case required operand[1] of i3 to
> be const0_rtx, now we can try a little tweaking of the code and
> constant, and see if it then changes to a cmp zero.
> 
> This abstracted patch was bootstrapped and tested independently on i686,
> to be sure it was only a reorg.
A reasonable cleanup.

I would suggest a minor addition the comment before
simplify_compare_const.  Specifically, the comment should say something
about the return value, including modification of *pop1.

Consider the patch pre-approved with the comment addition.

Thanks,
Jeff

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Patch

Index: combine.c
===================================================================
--- combine.c	(revision 172860)
+++ combine.c	(working copy)
@@ -450,6 +450,7 @@ 
 				 int);
 static int recog_for_combine (rtx *, rtx, rtx *);
 static rtx gen_lowpart_for_combine (enum machine_mode, rtx);
+static enum rtx_code simplify_compare_const (enum rtx_code, rtx, rtx *);
 static enum rtx_code simplify_comparison (enum rtx_code, rtx *, rtx *);
 static void update_table_tick (rtx);
 static void record_value_for_reg (rtx, rtx, rtx);
@@ -10808,6 +10840,188 @@ 
   return gen_rtx_CLOBBER (omode, const0_rtx);
 }
 
+/* Try to simplify a comparison between OP0 and a constant OP1,
+   where CODE is the comparison code that will be tested, into a
+   (CODE OP0 const0_rtx) form.  */
+
+static enum rtx_code
+simplify_compare_const (enum rtx_code code, rtx op0, rtx *pop1)
+{
+  enum machine_mode mode = GET_MODE (op0);
+  unsigned int mode_width = GET_MODE_BITSIZE (mode);
+  HOST_WIDE_INT const_op = INTVAL (*pop1);
+
+  /* Get the constant we are comparing against and turn off all bits
+     not on in our mode.  */
+  if (mode != VOIDmode)
+    const_op = trunc_int_for_mode (const_op, mode);
+
+  /* If we are comparing against a constant power of two and the value
+     being compared can only have that single bit nonzero (e.g., it was
+     `and'ed with that bit), we can replace this with a comparison
+     with zero.  */
+  if (const_op
+      && (code == EQ || code == NE || code == GE || code == GEU
+	  || code == LT || code == LTU)
+      && mode_width <= HOST_BITS_PER_WIDE_INT
+      && exact_log2 (const_op) >= 0
+      && nonzero_bits (op0, mode) == (unsigned HOST_WIDE_INT) const_op)
+    {
+      code = (code == EQ || code == GE || code == GEU ? NE : EQ);
+      const_op = 0;
+    }
+
+  /* Similarly, if we are comparing a value known to be either -1 or
+     0 with -1, change it to the opposite comparison against zero.  */
+  if (const_op == -1
+      && (code == EQ || code == NE || code == GT || code == LE
+	  || code == GEU || code == LTU)
+      && num_sign_bit_copies (op0, mode) == mode_width)
+    {
+      code = (code == EQ || code == LE || code == GEU ? NE : EQ);
+      const_op = 0;
+    }
+
+  /* Do some canonicalizations based on the comparison code.  We prefer
+     comparisons against zero and then prefer equality comparisons.
+     If we can reduce the size of a constant, we will do that too.  */
+  switch (code)
+    {
+    case LT:
+      /* < C is equivalent to <= (C - 1) */
+      if (const_op > 0)
+	{
+	  const_op -= 1;
+	  code = LE;
+	  /* ... fall through to LE case below.  */
+	}
+      else
+	break;
+
+    case LE:
+      /* <= C is equivalent to < (C + 1); we do this for C < 0  */
+      if (const_op < 0)
+	{
+	  const_op += 1;
+	  code = LT;
+	}
+
+      /* If we are doing a <= 0 comparison on a value known to have
+	 a zero sign bit, we can replace this with == 0.  */
+      else if (const_op == 0
+	       && mode_width <= HOST_BITS_PER_WIDE_INT
+	       && (nonzero_bits (op0, mode)
+		   & ((unsigned HOST_WIDE_INT) 1 << (mode_width - 1)))
+	       == 0)
+	code = EQ;
+      break;
+
+    case GE:
+      /* >= C is equivalent to > (C - 1).  */
+      if (const_op > 0)
+	{
+	  const_op -= 1;
+	  code = GT;
+	  /* ... fall through to GT below.  */
+	}
+      else
+	break;
+
+    case GT:
+      /* > C is equivalent to >= (C + 1); we do this for C < 0.  */
+      if (const_op < 0)
+	{
+	  const_op += 1;
+	  code = GE;
+	}
+
+      /* If we are doing a > 0 comparison on a value known to have
+	 a zero sign bit, we can replace this with != 0.  */
+      else if (const_op == 0
+	       && mode_width <= HOST_BITS_PER_WIDE_INT
+	       && (nonzero_bits (op0, mode)
+		   & ((unsigned HOST_WIDE_INT) 1 << (mode_width - 1)))
+	       == 0)
+	code = NE;
+      break;
+
+    case LTU:
+      /* < C is equivalent to <= (C - 1).  */
+      if (const_op > 0)
+	{
+	  const_op -= 1;
+	  code = LEU;
+	  /* ... fall through ...  */
+	}
+      /* (unsigned) < 0x80000000 is equivalent to >= 0.  */
+      else if (mode_width <= HOST_BITS_PER_WIDE_INT
+	       && (unsigned HOST_WIDE_INT) const_op
+	       == (unsigned HOST_WIDE_INT) 1 << (mode_width - 1))
+	{
+	  const_op = 0;
+	  code = GE;
+	  break;
+	}
+      else
+	break;
+
+    case LEU:
+      /* unsigned <= 0 is equivalent to == 0 */
+      if (const_op == 0)
+	code = EQ;
+      /* (unsigned) <= 0x7fffffff is equivalent to >= 0.  */
+      else if (mode_width <= HOST_BITS_PER_WIDE_INT
+	       && (unsigned HOST_WIDE_INT) const_op
+	       == ((unsigned HOST_WIDE_INT) 1 << (mode_width - 1)) - 1)
+	{
+	  const_op = 0;
+	  code = GE;
+	}
+      break;
+
+    case GEU:
+      /* >= C is equivalent to > (C - 1).  */
+      if (const_op > 1)
+	{
+	  const_op -= 1;
+	  code = GTU;
+	  /* ... fall through ...  */
+	}
+
+      /* (unsigned) >= 0x80000000 is equivalent to < 0.  */
+      else if (mode_width <= HOST_BITS_PER_WIDE_INT
+	       && (unsigned HOST_WIDE_INT) const_op
+	       == (unsigned HOST_WIDE_INT) 1 << (mode_width - 1))
+	{
+	  const_op = 0;
+	  code = LT;
+	  break;
+	}
+      else
+	break;
+
+    case GTU:
+      /* unsigned > 0 is equivalent to != 0 */
+      if (const_op == 0)
+	code = NE;
+      /* (unsigned) > 0x7fffffff is equivalent to < 0.  */
+      else if (mode_width <= HOST_BITS_PER_WIDE_INT
+	       && (unsigned HOST_WIDE_INT) const_op
+	       == ((unsigned HOST_WIDE_INT) 1 << (mode_width - 1)) - 1)
+	{
+	  const_op = 0;
+	  code = LT;
+	}
+      break;
+
+    default:
+      break;
+    }
+
+  *pop1 = GEN_INT (const_op);
+  return code;
+}
+
 /* Simplify a comparison between *POP0 and *POP1 where CODE is the
    comparison code that will be tested.
 
@@ -10997,186 +11211,11 @@ 
 		&& (GET_CODE (op0) == COMPARE || COMPARISON_P (op0))))
 	break;
 
-      /* Get the constant we are comparing against and turn off all bits
-	 not on in our mode.  */
+      /* Try to simplify the compare to constant, possibly changing the
+	 comparison op, and/or changing op1 to zero.  */
+      code = simplify_compare_const (code, op0, &op1);
       const_op = INTVAL (op1);
-      if (mode != VOIDmode)
-	const_op = trunc_int_for_mode (const_op, mode);
-      op1 = GEN_INT (const_op);
 
-      /* If we are comparing against a constant power of two and the value
-	 being compared can only have that single bit nonzero (e.g., it was
-	 `and'ed with that bit), we can replace this with a comparison
-	 with zero.  */
-      if (const_op
-	  && (code == EQ || code == NE || code == GE || code == GEU
-	      || code == LT || code == LTU)
-	  && mode_width <= HOST_BITS_PER_WIDE_INT
-	  && exact_log2 (const_op) >= 0
-	  && nonzero_bits (op0, mode) == (unsigned HOST_WIDE_INT) const_op)
-	{
-	  code = (code == EQ || code == GE || code == GEU ? NE : EQ);
-	  op1 = const0_rtx, const_op = 0;
-	}
-
-      /* Similarly, if we are comparing a value known to be either -1 or
-	 0 with -1, change it to the opposite comparison against zero.  */
-
-      if (const_op == -1
-	  && (code == EQ || code == NE || code == GT || code == LE
-	      || code == GEU || code == LTU)
-	  && num_sign_bit_copies (op0, mode) == mode_width)
-	{
-	  code = (code == EQ || code == LE || code == GEU ? NE : EQ);
-	  op1 = const0_rtx, const_op = 0;
-	}
-
-      /* Do some canonicalizations based on the comparison code.  We prefer
-	 comparisons against zero and then prefer equality comparisons.
-	 If we can reduce the size of a constant, we will do that too.  */
-
-      switch (code)
-	{
-	case LT:
-	  /* < C is equivalent to <= (C - 1) */
-	  if (const_op > 0)
-	    {
-	      const_op -= 1;
-	      op1 = GEN_INT (const_op);
-	      code = LE;
-	      /* ... fall through to LE case below.  */
-	    }
-	  else
-	    break;
-
-	case LE:
-	  /* <= C is equivalent to < (C + 1); we do this for C < 0  */
-	  if (const_op < 0)
-	    {
-	      const_op += 1;
-	      op1 = GEN_INT (const_op);
-	      code = LT;
-	    }
-
-	  /* If we are doing a <= 0 comparison on a value known to have
-	     a zero sign bit, we can replace this with == 0.  */
-	  else if (const_op == 0
-		   && mode_width <= HOST_BITS_PER_WIDE_INT
-		   && (nonzero_bits (op0, mode)
-		       & ((unsigned HOST_WIDE_INT) 1 << (mode_width - 1)))
-		         == 0)
-	    code = EQ;
-	  break;
-
-	case GE:
-	  /* >= C is equivalent to > (C - 1).  */
-	  if (const_op > 0)
-	    {
-	      const_op -= 1;
-	      op1 = GEN_INT (const_op);
-	      code = GT;
-	      /* ... fall through to GT below.  */
-	    }
-	  else
-	    break;
-
-	case GT:
-	  /* > C is equivalent to >= (C + 1); we do this for C < 0.  */
-	  if (const_op < 0)
-	    {
-	      const_op += 1;
-	      op1 = GEN_INT (const_op);
-	      code = GE;
-	    }
-
-	  /* If we are doing a > 0 comparison on a value known to have
-	     a zero sign bit, we can replace this with != 0.  */
-	  else if (const_op == 0
-		   && mode_width <= HOST_BITS_PER_WIDE_INT
-		   && (nonzero_bits (op0, mode)
-		       & ((unsigned HOST_WIDE_INT) 1 << (mode_width - 1)))
-		       == 0)
-	    code = NE;
-	  break;
-
-	case LTU:
-	  /* < C is equivalent to <= (C - 1).  */
-	  if (const_op > 0)
-	    {
-	      const_op -= 1;
-	      op1 = GEN_INT (const_op);
-	      code = LEU;
-	      /* ... fall through ...  */
-	    }
-
-	  /* (unsigned) < 0x80000000 is equivalent to >= 0.  */
-	  else if (mode_width <= HOST_BITS_PER_WIDE_INT
-		   && (unsigned HOST_WIDE_INT) const_op
-		      == (unsigned HOST_WIDE_INT) 1 << (mode_width - 1))
-	    {
-	      const_op = 0, op1 = const0_rtx;
-	      code = GE;
-	      break;
-	    }
-	  else
-	    break;
-
-	case LEU:
-	  /* unsigned <= 0 is equivalent to == 0 */
-	  if (const_op == 0)
-	    code = EQ;
-
-	  /* (unsigned) <= 0x7fffffff is equivalent to >= 0.  */
-	  else if (mode_width <= HOST_BITS_PER_WIDE_INT
-		   && (unsigned HOST_WIDE_INT) const_op
-		      == ((unsigned HOST_WIDE_INT) 1 << (mode_width - 1)) - 1)
-	    {
-	      const_op = 0, op1 = const0_rtx;
-	      code = GE;
-	    }
-	  break;
-
-	case GEU:
-	  /* >= C is equivalent to > (C - 1).  */
-	  if (const_op > 1)
-	    {
-	      const_op -= 1;
-	      op1 = GEN_INT (const_op);
-	      code = GTU;
-	      /* ... fall through ...  */
-	    }
-
-	  /* (unsigned) >= 0x80000000 is equivalent to < 0.  */
-	  else if (mode_width <= HOST_BITS_PER_WIDE_INT
-		   && (unsigned HOST_WIDE_INT) const_op
-		      == (unsigned HOST_WIDE_INT) 1 << (mode_width - 1))
-	    {
-	      const_op = 0, op1 = const0_rtx;
-	      code = LT;
-	      break;
-	    }
-	  else
-	    break;
-
-	case GTU:
-	  /* unsigned > 0 is equivalent to != 0 */
-	  if (const_op == 0)
-	    code = NE;
-
-	  /* (unsigned) > 0x7fffffff is equivalent to < 0.  */
-	  else if (mode_width <= HOST_BITS_PER_WIDE_INT
-		   && (unsigned HOST_WIDE_INT) const_op
-		      == ((unsigned HOST_WIDE_INT) 1 << (mode_width - 1)) - 1)
-	    {
-	      const_op = 0, op1 = const0_rtx;
-	      code = LT;
-	    }
-	  break;
-
-	default:
-	  break;
-	}
-
       /* Compute some predicates to simplify code below.  */
 
       equality_comparison_p = (code == EQ || code == NE);