On Tue, Jan 13, 2015 at 11:47 PM, Andrew Pinski <pins...@gmail.com> wrote: > On Tue, Jan 13, 2015 at 2:41 PM, Rasmus Villemoes <r...@rasmusvillemoes.dk> > wrote: >> [My first attempt at submitting a patch for gcc, so please forgive me >> if I'm not following the right protocol.] > > There are a few things missing. For one, a testcase or two for the > added optimizations. > >> >> Sometimes rounding a variable to the next even integer is written x += x >> & 1. This usually means using an extra register (and hence at least an >> extra mov instruction) compared to the equivalent x = (x + 1) & ~1. The >> first pattern below tries to do this transformation. >> >> While playing with various ways of rounding down, I noticed that gcc >> already optimizes all of x-(x&3), x^(x&3) and x&~(x&3) to simply >> x&~3.
Does it also handle x+(x&3)? Where does it handle x - (x&3)? That is, doesn't the pattern also work for constants other than 1? Please put it before the abs simplifications after the last one handing bit_and/bit_ior. Thanks, Richard. > In fact, x&~(x&y) is rewritten as x&~y. However, the dual of this >> is not handled, so I included the second pattern below. >> >> I've tested the below in the sense that gcc compiles and that trivial >> test cases get compiled as expected. > > The other thing you missed is a changelog entry for the change you did. > Also you mentioned you tested the patch below but did not mention > which target you tested it on and you should run the full GCC > testsuite. > https://gcc.gnu.org/contribute.html is a good page to start with how > to handle most of the items above. > https://gcc.gnu.org/wiki/HowToPrepareATestcase is a good page on how > to write the testcase for testing the added optimization. > > Thanks, > Andrew Pinski > >> >> Rasmus >> >> >> >> diff --git gcc/match.pd gcc/match.pd >> index 81c4ee6..04a0bc4 100644 >> --- gcc/match.pd >> +++ gcc/match.pd >> @@ -262,6 +262,16 @@ along with GCC; see the file COPYING3. If not see >> (abs tree_expr_nonnegative_p@0) >> @0) >> >> +/* x + (x & 1) -> (x + 1) & ~1 */ >> +(simplify >> + (plus @0 (bit_and @0 integer_onep@1)) >> + (bit_and (plus @0 @1) (bit_not @1))) >> + >> +/* x | ~(x | y) -> x | ~y */ >> +(simplify >> + (bit_ior @0 (bit_not (bit_ior @0 @1))) >> + (bit_ior @0 (bit_not @1))) >> + >> >> /* Try to fold (type) X op CST -> (type) (X op ((type-x) CST)) >> when profitable.
