| Message ID | SN2PR0701MB1024719A5C46B8E7276E718C8E920@SN2PR0701MB1024.namprd07.prod.outlook.com |
|---|---|
| State | New |
| Headers | show |
On Tue, Jul 7, 2015 at 6:52 AM, Hurugalawadi, Naveen <Naveen.Hurugalawadi@caviumnetworks.com> wrote: > Hi, > > Please find attached the patch PR25530.patch that converts the pattern:- > (unsigned / 2) * 2 is into (unsigned & ~1). > > Please review and let me know if its okay. For EXACT_DIV fold-const.c has /* ((T) (X /[ex] C)) * C cancels out if the conversion is sign-changing only. */ if (TREE_CODE (arg1) == INTEGER_CST && TREE_CODE (arg0) == EXACT_DIV_EXPR && operand_equal_p (arg1, TREE_OPERAND (arg0, 1), 0)) return fold_convert_loc (loc, type, TREE_OPERAND (arg0, 0)); we know the remainder is zero for EXACT_DIV. It also gives hints that a sign-changing conversion is ok. +/* Simplify (unsigned t / 2) * 2 -> unsigned t & ~1. */ +/* PR25530. */ +(for div (trunc_div ceil_div floor_div round_div exact_div) + (simplify + (mult (div @0 INTEGER_CST@1) INTEGER_CST@1) + (with { tree n2 = build_int_cst (TREE_TYPE (@0), + wi::exact_log2 (@1)); } + (if (TYPE_UNSIGNED (TREE_TYPE (@0))) + (bit_and @0 (lshift (rshift { build_minus_one_cst (TREE_TYPE (@0)); } + { n2; }) { n2; })))))) you should move the (with inside the (if to save work if the type is not unsigned. Also you are using wi::exact_log2 without checking whether @1 was a power of two (I think exact_log2 returns -1 in this case). Then expressing ~1 with the result expression is really excessive - you should simply build this with @1 - 1 if @1 is a power of two. So please handle exact_div differently, like fold-const.c does. Also I am not sure ceil_div and floor_div can be handled this way. (5 /[ceil] 2) * 2 == 6 but you compute it as 4. So I am only convinced trunc_div works this way. Thanks, Richard. > Regression tested on AARH64 and x86_64. > > Thanks, > Naveen > > gcc/testsuite/ChangeLog: > > 2015-07-07 Naveen H.S <Naveen.Hurugalawadi@caviumnetworks.com> > > PR middle-end/25530 > * gcc.dg/pr25530.c: New test. > > gcc/ChangeLog: > > 2015-07-07 Naveen H.S <Naveen.Hurugalawadi@caviumnetworks.com> > > PR middle-end/25530 > * match.pd (mult (div @0 INTEGER_CST@1) INTEGER_CST@1) : > New simplifier.
On 07/07/2015 11:08, Richard Biener wrote: > Also I am not sure ceil_div and floor_div can be handled this way. > (5 /[ceil] 2) * 2 == 6 but you compute it as 4. So I am only convinced > trunc_div works this way. Of course also floor_div for unsigned arguments. For signed arguments, ceil_div works if the operand is known-negative and floor_div if known-positive. Perhaps you could optimize these cases to trunc_div first (or maybe it's already done...)? Paolo
On Thu, Jul 9, 2015 at 8:35 AM, Paolo Bonzini <bonzini@gnu.org> wrote: > > > On 07/07/2015 11:08, Richard Biener wrote: >> Also I am not sure ceil_div and floor_div can be handled this way. >> (5 /[ceil] 2) * 2 == 6 but you compute it as 4. So I am only convinced >> trunc_div works this way. > > Of course also floor_div for unsigned arguments. > > For signed arguments, ceil_div works if the operand is known-negative > and floor_div if known-positive. > > Perhaps you could optimize these cases to trunc_div first (or maybe it's > already done...)? fold-const.c does this already, yes. Richard. > Paolo
diff --git a/gcc/match.pd b/gcc/match.pd index 53e911a..2c9e408 100644 --- a/gcc/match.pd +++ b/gcc/match.pd @@ -529,6 +529,17 @@ along with GCC; see the file COPYING3. If not see (bitop (bit_and:c @0 @1) (bit_and @2 @1)) (bit_and (bitop @0 @2) @1))) +/* Simplify (unsigned t / 2) * 2 -> unsigned t & ~1. */ +/* PR25530. */ +(for div (trunc_div ceil_div floor_div round_div exact_div) + (simplify + (mult (div @0 INTEGER_CST@1) INTEGER_CST@1) + (with { tree n2 = build_int_cst (TREE_TYPE (@0), + wi::exact_log2 (@1)); } + (if (TYPE_UNSIGNED (TREE_TYPE (@0))) + (bit_and @0 (lshift (rshift { build_minus_one_cst (TREE_TYPE (@0)); } + { n2; }) { n2; })))))) + /* (x | CST1) & CST2 -> (x & CST2) | (CST1 & CST2) */ (simplify (bit_and (bit_ior @0 CONSTANT_CLASS_P@1) CONSTANT_CLASS_P@2) diff --git a/gcc/testsuite/gcc.dg/pr25530.c b/gcc/testsuite/gcc.dg/pr25530.c new file mode 100644 index 0000000..61e19cc --- /dev/null +++ b/gcc/testsuite/gcc.dg/pr25530.c @@ -0,0 +1,10 @@ +/* { dg-do compile } */ +/* { dg-options "-O2 -fdump-tree-optimized" } */ + +int +f (unsigned t) +{ + return (t / 2) * 2; +} + +/* { dg-final { scan-tree-dump "\& -2" "optimized" } } */