On Fri, 26 Jun 2015, Marek Polacek wrote:
This is an attempt to move one pattern from fold-const.c to match.pd.
It ought to be 1:1, but is not, e.g. with this patch we won't fold e.g.
int
f (int a, int b)
{
return a - (unsigned) ((a / b) * b)
}
anymore, but we're able to fold
int
ff (int a, unsigned int b)
{
return a - ((a / b) * b);
}
and fold-const.c is not. I played around with converts, but didn't find
anything that would work well. Any suggestions how to make this pattern
better?
Anything wrong with this?
+/* X - (X / Y) * Y is the same as X % Y. */
+(simplify
+ (minus (convert? @0) (convert? (mult (trunc_div @0 @1) @1)))
+ (if (INTEGRAL_TYPE_P (type) || VECTOR_INTEGER_TYPE_P (type))
+ (convert (trunc_mod @0 @1))))
(the other div/mod pairs could benefit from the same transformation as
long as there are no conversions, but the conversion seems easier to
handle with trunc_)
diff --git gcc/match.pd gcc/match.pd
index b2f8429..2bc158b 100644
--- gcc/match.pd
+++ gcc/match.pd
@@ -238,6 +238,12 @@ along with GCC; see the file COPYING3. If not see
&& tree_nop_conversion_p (type, TREE_TYPE (@1)))
(trunc_mod @0 (convert @1))))
+/* X - (X / Y) * Y is the same as X % Y. */
+(simplify
+ (minus @0 (mult (trunc_div @0 @1) @1))
+ (if (INTEGRAL_TYPE_P (type) || VECTOR_INTEGER_TYPE_P (type))
+ (trunc_mod @0 @1)))
+
/* Optimize TRUNC_MOD_EXPR by a power of two into a BIT_AND_EXPR,
i.e. "X % C" into "X & (C - 1)", if X and C are positive.
Also optimize A % (C << N) where C is a power of 2,
Marek
--
Marc Glisse
