On Thu, 30 Apr 2015, Richard Biener wrote:
On Wed, Jan 21, 2015 at 11:49 AM, Rasmus Villemoes
<r...@rasmusvillemoes.dk> wrote:
Generalizing the x+(x&1) pattern, one can round up x to a multiple of
a 2^k by adding the negative of x modulo 2^k. But it is fewer
instructions, and presumably requires fewer registers, to do the more
common (x+m)&~m where m=2^k-1.
Signed-off-by: Rasmus Villemoes <r...@rasmusvillemoes.dk>
---
gcc/match.pd | 9 ++++++
gcc/testsuite/gcc.dg/20150120-4.c | 59 +++++++++++++++++++++++++++++++++++++++
2 files changed, 68 insertions(+)
create mode 100644 gcc/testsuite/gcc.dg/20150120-4.c
diff --git gcc/match.pd gcc/match.pd
index 47865f1..93c2298 100644
--- gcc/match.pd
+++ gcc/match.pd
@@ -273,6 +273,15 @@ along with GCC; see the file COPYING3. If not see
(if (TREE_CODE (@2) != SSA_NAME || has_single_use (@2))
(bit_ior @0 (bit_not @1))))
+/* x + ((-x) & m) -> (x + m) & ~m when m == 2^k-1. */
+(simplify
+ (plus:c @0 (bit_and@2 (negate @0) CONSTANT_CLASS_P@1))
I think you want to restrict this to INTEGER_CST@1
Is this only to make the following test easier (a good enough reason for
me) or is there some fundamental reason why this transformation would be
wrong for vectors?
+ (with { tree cst = fold_binary (PLUS_EXPR, TREE_TYPE (@1),
+ @1, build_one_cst (TREE_TYPE (@1))); }
We shouldn't dispatch to fold_binary in patterns. int_const_binop would
be the appropriate function to use - but what happens for @1 == INT_MAX
where @1 + 1 overflows? Similar, is this also valid for negative @1
and thus signed mask types? IMHO we should check whether @1
is equal to wi::mask (TYPE_PRECISION (TREE_TYPE (@1)) - wi::clz (@1),
false, TYPE_PRECISION (TREE_TYPE (@1)).
As with the other patch a ChangeLog entry is missing as well as stating
how you tested the patch.
Thanks,
Richard.
+ (if ((TREE_CODE (@2) != SSA_NAME || has_single_use (@2))
+ && cst && integer_pow2p (cst))
+ (bit_and (plus @0 @1) (bit_not @1)))))
--
Marc Glisse
