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[2/4] Use tree_to_uhwi when folding (x >> c) << c

Message ID 87pppwob30.fsf@talisman.default
State New
Headers show

Commit Message

Richard Sandiford Nov. 19, 2013, noon UTC 
The (x >> c) << c folding has:

	  && tree_fits_shwi_p (arg1)
	  && TREE_INT_CST_LOW (arg1) < prec
	  && tree_fits_shwi_p (TREE_OPERAND (arg0, 1))
	  && TREE_INT_CST_LOW (TREE_OPERAND (arg0, 1)) < prec)

At first glance the use of tree_fits_shwi_p rather than tree_fits_uhwi_p
made me think this allows negative shift counts, but of course TREE_INT_CST_LOW
is unsigned.  I think it'd be clearer to use tree_fits_uhwi_p instead.

Thanks,
Richard


gcc/
	* fold-const.c (fold_binary_loc): Use unsigned rather than signed
	HOST_WIDE_INTs when folding (x >> c) << c.

Comments

Jeff Law Nov. 19, 2013, 6:51 p.m. UTC | #1 
On 11/19/13 05:00, Richard Sandiford wrote:
> The (x >> c) << c folding has:
>
> 	  && tree_fits_shwi_p (arg1)
> 	  && TREE_INT_CST_LOW (arg1) < prec
> 	  && tree_fits_shwi_p (TREE_OPERAND (arg0, 1))
> 	  && TREE_INT_CST_LOW (TREE_OPERAND (arg0, 1)) < prec)
>
> At first glance the use of tree_fits_shwi_p rather than tree_fits_uhwi_p
> made me think this allows negative shift counts, but of course TREE_INT_CST_LOW
> is unsigned.  I think it'd be clearer to use tree_fits_uhwi_p instead.
>
> Thanks,
> Richard
>
>
> gcc/
> 	* fold-const.c (fold_binary_loc): Use unsigned rather than signed
> 	HOST_WIDE_INTs when folding (x >> c) << c.
OK.
jeff
diff mbox

Patch

Index: gcc/fold-const.c
===================================================================
--- gcc/fold-const.c	2013-11-19 10:53:54.965643984 +0000
+++ gcc/fold-const.c	2013-11-19 11:59:33.611252297 +0000
@@ -12676,13 +12676,13 @@  fold_binary_loc (location_t loc,
       if (((code == LSHIFT_EXPR && TREE_CODE (arg0) == RSHIFT_EXPR)
            || (TYPE_UNSIGNED (type)
 	       && code == RSHIFT_EXPR && TREE_CODE (arg0) == LSHIFT_EXPR))
-	  && tree_fits_shwi_p (arg1)
-	  && TREE_INT_CST_LOW (arg1) < prec
-	  && tree_fits_shwi_p (TREE_OPERAND (arg0, 1))
-	  && TREE_INT_CST_LOW (TREE_OPERAND (arg0, 1)) < prec)
+	  && tree_fits_uhwi_p (arg1)
+	  && tree_to_uhwi (arg1) < prec
+	  && tree_fits_uhwi_p (TREE_OPERAND (arg0, 1))
+	  && tree_to_uhwi (TREE_OPERAND (arg0, 1)) < prec)
 	{
-	  HOST_WIDE_INT low0 = TREE_INT_CST_LOW (TREE_OPERAND (arg0, 1));
-	  HOST_WIDE_INT low1 = TREE_INT_CST_LOW (arg1);
+	  HOST_WIDE_INT low0 = tree_to_uhwi (TREE_OPERAND (arg0, 1));
+	  HOST_WIDE_INT low1 = tree_to_uhwi (arg1);
 	  tree lshift;
 	  tree arg00;