On Thu, 1 Jun 2023, Jiufu Guo wrote:
> Hi,
>
> Jiufu Guo via Gcc-patches <gcc-patches@gcc.gnu.org> writes:
>
> > Hi,
> >
> > Richard Biener <rguent...@suse.de> writes:
> >
> >> On Wed, 17 May 2023, Jiufu Guo wrote:
> >>
> >>> Hi,
> >>>
> >>> This patch tries to optimize "(X - N * M) / N + M" to "X / N".
> >>
> >> But if that's valid why not make the transform simpler and transform
> >> (X - N * M) / N to X / N - M instead?
> >
> > Great catch!
> > If "N * M" is not constant, "X / N - M" would be better than
> > "(X - N * M) / N". If "N, M" are constants, "(X - N * M) / N" and
> > "X / N - M" may be similar; while for this case, "X / N - M" should
> > also be fine! I would try to update accordingly.
> >
> >>
> >> You use the same optimize_x_minus_NM_div_N_plus_M validator for
> >> the division and shift variants but the overflow rules are different,
> >> so I'm not sure that's warranted. I'd also prefer to not split out
> >> the validator to a different file - iff then the appropriate file
> >> is fold-const.cc, not gimple-match-head.cc (I see we're a bit
> >> inconsistent here, for pure gimple matches gimple-fold.cc would
> >> be another place).
> >
> > Thanks for pointing out this!
> > For shift, I guess you may concern that: 1. if the right operand is
> > negative or is greater than or equal to the type width. 2. if it is
> > a signed negative value. They may UB or 'sign bit shift'? This patch
> > assumes it is ok to do the transform. I may have more check to see
> > if this is really ok, and hope some one can point out if this is
> > invalid. "(X - N * M) >> log2(N)" ==> " X >> log2(N) - M".
> >
> > I split out the validator just because: it is shared for division and
> > shift :). And it seems gimple-match-head.cc and generic-match-head.cc,
> > may be introduced for match.pd. So, I put it into gimple-match-head.cc.
> >
> >>
> >> Since you use range information why is the transform restricted
> >> to constant M?
> >
> > If M is a variable, the range for "X" is varying_p. I did not find
> > the method to get the bounds for "X" (or for "X - N * M") to check no
> > wraps. Any suggestions?
>
> Oh, I may misunderstand here.
> You may say: M could be with a range too, then we can check if
> "X - N * M" has a valid range or possible wrap/overflow.
Yes.
Richard.
> BR,
> Jeff (Jiufu Guo)
>
> >
> >
> > Again, thanks for your great help!
> >
> > BR,
> > Jeff (Jiufu Guo)
> >
> >>
> >> Richard.
> >>
> >>> As per the discussions in PR108757, we know this transformation is valid
> >>> only under some conditions.
> >>> For C code, "/" towards zero (trunc_div), and "X - N * M"
> >>> maybe wrap/overflow/underflow. So, it is valid that "X - N * M" does
> >>> not cross zero and does not wrap/overflow/underflow.
> >>>
> >>> This patch also handles the case when "N" is the power of 2, where
> >>> "(X - N * M) / N" is "(X - N * M) >> log2(N)".
> >>>
> >>> Bootstrap & regtest pass on ppc64{,le} and x86_64.
> >>> Is this ok for trunk?
> >>>
> >>> BR,
> >>> Jeff (Jiufu)
> >>>
> >>> PR tree-optimization/108757
> >>>
> >>> gcc/ChangeLog:
> >>>
> >>> * gimple-match-head.cc (optimize_x_minus_NM_div_N_plus_M): New function.
> >>> * match.pd ((X - N * M) / N + M): New pattern.
> >>>
> >>> gcc/testsuite/ChangeLog:
> >>>
> >>> * gcc.dg/pr108757-1.c: New test.
> >>> * gcc.dg/pr108757-2.c: New test.
> >>> * gcc.dg/pr108757.h: New test.
> >>>
> >>> ---
> >>> gcc/gimple-match-head.cc | 54 ++++++++++
> >>> gcc/match.pd | 22 ++++
> >>> gcc/testsuite/gcc.dg/pr108757-1.c | 17 ++++
> >>> gcc/testsuite/gcc.dg/pr108757-2.c | 18 ++++
> >>> gcc/testsuite/gcc.dg/pr108757.h | 160 ++++++++++++++++++++++++++++++
> >>> 5 files changed, 271 insertions(+)
> >>> create mode 100644 gcc/testsuite/gcc.dg/pr108757-1.c
> >>> create mode 100644 gcc/testsuite/gcc.dg/pr108757-2.c
> >>> create mode 100644 gcc/testsuite/gcc.dg/pr108757.h
> >>>
> >>> diff --git a/gcc/gimple-match-head.cc b/gcc/gimple-match-head.cc
> >>> index b08cd891a13..680a4cb2fc6 100644
> >>> --- a/gcc/gimple-match-head.cc
> >>> +++ b/gcc/gimple-match-head.cc
> >>> @@ -224,3 +224,57 @@ optimize_successive_divisions_p (tree divisor, tree
> >>> inner_div)
> >>> }
> >>> return true;
> >>> }
> >>> +
> >>> +/* Return true if "(X - N * M) / N + M" can be optimized into "X / N".
> >>> + Otherwise return false.
> >>> +
> >>> + For unsigned,
> >>> + If sign bit of M is 0 (clz is 0), valid range is [N*M, MAX].
> >>> + If sign bit of M is 1, valid range is [0, MAX - N*(-M)].
> >>> +
> >>> + For signed,
> >>> + If N*M > 0, valid range: [MIN+N*M, 0] + [N*M, MAX]
> >>> + If N*M < 0, valid range: [MIN, -(-N*M)] + [0, MAX - (-N*M)]. */
> >>> +
> >>> +static bool
> >>> +optimize_x_minus_NM_div_N_plus_M (tree x, wide_int n, wide_int m, tree
> >>> type)
> >>> +{
> >>> + wide_int max = wi::max_value (type);
> >>> + signop sgn = TYPE_SIGN (type);
> >>> + wide_int nm;
> >>> + wi::overflow_type ovf;
> >>> + if (TYPE_UNSIGNED (type) && wi::clz (m) == 0)
> >>> + nm = wi::mul (n, -m, sgn, &ovf);
> >>> + else
> >>> + nm = wi::mul (n, m, sgn, &ovf);
> >>> +
> >>> + if (ovf != wi::OVF_NONE)
> >>> + return false;
> >>> +
> >>> + value_range vr0;
> >>> + if (!get_range_query (cfun)->range_of_expr (vr0, x) || vr0.varying_p ()
> >>> + || vr0.undefined_p ())
> >>> + return false;
> >>> +
> >>> + wide_int wmin0 = vr0.lower_bound ();
> >>> + wide_int wmax0 = vr0.upper_bound ();
> >>> + wide_int min = wi::min_value (type);
> >>> +
> >>> + /* unsigned */
> >>> + if ((TYPE_UNSIGNED (type)))
> >>> + /* M > 0 (clz != 0): [N*M, MAX], M < 0 : [0, MAX-N*(-M)] */
> >>> + return wi::clz (m) != 0 ? wi::ge_p (wmin0, nm, sgn)
> >>> + : wi::le_p (wmax0, max - nm, sgn);
> >>> +
> >>> + /* signed, N*M > 0 */
> >>> + else if (wi::gt_p (nm, 0, sgn))
> >>> + /* [N*M, MAX] or [MIN+N*M, 0] */
> >>> + return wi::ge_p (wmin0, nm, sgn)
> >>> + || (wi::ge_p (wmin0, min + nm, sgn) && wi::le_p (wmax0, 0, sgn));
> >>> +
> >>> + /* signed, N*M < 0 */
> >>> + /* [MIN, N*M] or [0, MAX + N*M]*/
> >>> + else
> >>> + return wi::le_p (wmax0, nm, sgn)
> >>> + || (wi::ge_p (wmin0, 0, sgn) && wi::le_p (wmax0, max - (-nm), sgn));
> >>> +}
> >>> diff --git a/gcc/match.pd b/gcc/match.pd
> >>> index ceae1c34abc..1aaa5530577 100644
> >>> --- a/gcc/match.pd
> >>> +++ b/gcc/match.pd
> >>> @@ -881,6 +881,28 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
> >>> #endif
> >>> ))))
> >>>
> >>> +#if GIMPLE
> >>> +/* Simplify ((t + -N*M) / N + M) -> t / N. */
> >>> +(for div (trunc_div exact_div)
> >>> + (simplify
> >>> + (plus (div (plus @0 INTEGER_CST@1) INTEGER_CST@2) INTEGER_CST@3)
> >>> + (with {wide_int n = wi::to_wide (@2); wide_int m = wi::to_wide (@3);}
> >>> + (if (INTEGRAL_TYPE_P (type)
> >>> + && n * m == -wi::to_wide (@1)
> >>> + && optimize_x_minus_NM_div_N_plus_M (@0, n, m, type))
> >>> + (div @0 @2)))))
> >>> +
> >>> +/* Simplify ((t + -(M<<N)) >> N + M) -> t >> N. */
> >>> +(simplify
> >>> + (plus (rshift (plus @0 INTEGER_CST@1) INTEGER_CST@2) INTEGER_CST@3)
> >>> + (with {wide_int n = wi::to_wide (@2); wide_int m = wi::to_wide (@3);}
> >>> + (if (INTEGRAL_TYPE_P (type)
> >>> + && (m << n) == -wi::to_wide (@1)
> >>> + && optimize_x_minus_NM_div_N_plus_M (@0,
> >>> + wi::one (TYPE_PRECISION (type)) << n, m, type))
> >>> + (rshift @0 @2))))
> >>> +#endif
> >>> +
> >>> (for op (negate abs)
> >>> /* Simplify cos(-x) and cos(|x|) -> cos(x). Similarly for cosh. */
> >>> (for coss (COS COSH)
> >>> diff --git a/gcc/testsuite/gcc.dg/pr108757-1.c
> >>> b/gcc/testsuite/gcc.dg/pr108757-1.c
> >>> new file mode 100644
> >>> index 00000000000..349318a7c82
> >>> --- /dev/null
> >>> +++ b/gcc/testsuite/gcc.dg/pr108757-1.c
> >>> @@ -0,0 +1,17 @@
> >>> +/* PR tree-optimization/108757 */
> >>> +/* { dg-do compile } */
> >>> +/* { dg-options "-O2 -fdump-tree-optimized" } */
> >>> +
> >>> +#include <limits.h>
> >>> +#define N 4
> >>> +#define M 3
> >>> +#define GAP 0
> >>> +typedef unsigned int UINT;
> >>> +typedef int INT;
> >>> +#define UMAX UINT_MAX
> >>> +#define IMAX INT_MAX
> >>> +#define IMIN INT_MIN
> >>> +#include "pr108757.h"
> >>> +
> >>> +/* { dg-final { scan-tree-dump-not " = x_\[0-9\]\\(D\\) \\+ "
> >>> "optimized" } } */
> >>> +/* { dg-final { scan-tree-dump-not " = b_\[0-9\] \\+ " "optimized" } } */
> >>> diff --git a/gcc/testsuite/gcc.dg/pr108757-2.c
> >>> b/gcc/testsuite/gcc.dg/pr108757-2.c
> >>> new file mode 100644
> >>> index 00000000000..7302e9c606c
> >>> --- /dev/null
> >>> +++ b/gcc/testsuite/gcc.dg/pr108757-2.c
> >>> @@ -0,0 +1,18 @@
> >>> +/* PR tree-optimization/108757 */
> >>> +/* { dg-do compile } */
> >>> +/* { dg-options "-O2 -fdump-tree-optimized" } */
> >>> +
> >>> +#include <limits.h>
> >>> +#define N 4
> >>> +#define M 3
> >>> +#define GAP 2
> >>> +typedef unsigned int UINT;
> >>> +typedef int INT;
> >>> +#define UMAX UINT_MAX
> >>> +#define IMAX INT_MAX
> >>> +#define IMIN INT_MIN
> >>> +#include "pr108757.h"
> >>> +
> >>> +/* { dg-final { scan-tree-dump-times " = x_\[0-9\]\\(D\\) \\+ " 16
> >>> "optimized" } } */
> >>> +/* { dg-final { scan-tree-dump-times " = b_\[0-9\] \\+ " 16 "optimized"
> >>> } } */
> >>> +
> >>> diff --git a/gcc/testsuite/gcc.dg/pr108757.h
> >>> b/gcc/testsuite/gcc.dg/pr108757.h
> >>> new file mode 100644
> >>> index 00000000000..9e12d106aad
> >>> --- /dev/null
> >>> +++ b/gcc/testsuite/gcc.dg/pr108757.h
> >>> @@ -0,0 +1,160 @@
> >>> +#define NOINLINE __attribute__ ((noinline))
> >>> +UINT NOINLINE
> >>> +opt_u1 (UINT x)
> >>> +{
> >>> + if (x < (M * N) - GAP)
> >>> + return 0;
> >>> + UINT a = x - (M * N);
> >>> + UINT b = a / N;
> >>> + return b + M;
> >>> +}
> >>> +
> >>> +UINT NOINLINE
> >>> +opt_u2 (UINT x)
> >>> +{
> >>> + if (x > (UMAX - (M * N) + GAP))
> >>> + return 0;
> >>> + UINT a = x + (M * N);
> >>> + UINT b = a / N;
> >>> + return b - M;
> >>> +}
> >>> +
> >>> +INT NOINLINE
> >>> +opt_s1 (INT x)
> >>> +{
> >>> + if (x < (M * N) - GAP)
> >>> + return 0;
> >>> + INT a = x - (M * N);
> >>> + INT b = a / N;
> >>> + return b + M;
> >>> +}
> >>> +
> >>> +INT NOINLINE
> >>> +opt_s2 (INT x)
> >>> +{
> >>> + if (x < IMIN + (M * N) - GAP || x > 0)
> >>> + return 0;
> >>> + INT a = x - (M * N);
> >>> + INT b = a / N;
> >>> + return b + M;
> >>> +}
> >>> +
> >>> +INT NOINLINE
> >>> +opt_s3 (INT x)
> >>> +{
> >>> + if (x < (M * N) - GAP)
> >>> + return 0;
> >>> + INT a = x - (M * N);
> >>> + INT b = a / -N;
> >>> + return b + -M;
> >>> +}
> >>> +
> >>> +INT NOINLINE
> >>> +opt_s4 (INT x)
> >>> +{
> >>> + if (x < IMIN + (M * N) - GAP || x > 0)
> >>> + return 0;
> >>> + INT a = x - (M * N);
> >>> + INT b = a / -N;
> >>> + return b + -M;
> >>> +}
> >>> +
> >>> +INT NOINLINE
> >>> +opt_s5 (INT x)
> >>> +{
> >>> + if (x > (-M * N) + GAP)
> >>> + return 0;
> >>> + INT a = x - (-M * N);
> >>> + INT b = a / N;
> >>> + return b + -M;
> >>> +}
> >>> +
> >>> +INT NOINLINE
> >>> +opt_s6 (INT x)
> >>> +{
> >>> + if (x > IMAX - (M * N) + GAP || x < 0)
> >>> + return 0;
> >>> + INT a = x - (-M * N);
> >>> + INT b = a / N;
> >>> + return b + -M;
> >>> +}
> >>> +
> >>> +INT NOINLINE
> >>> +opt_s7 (INT x)
> >>> +{
> >>> + if (x > (M * -N) + GAP)
> >>> + return 0;
> >>> + INT a = x - (M * -N);
> >>> + INT b = a / -N;
> >>> + return b + M;
> >>> +}
> >>> +
> >>> +INT NOINLINE
> >>> +opt_s8 (INT x)
> >>> +{
> >>> + if (x > IMAX - (M * N) + GAP || x < 0)
> >>> + return 0;
> >>> + INT a = x - (M * -N);
> >>> + INT b = a / -N;
> >>> + return b + M;
> >>> +}
> >>> +
> >>> +UINT NOINLINE
> >>> +opt_u3 (UINT x)
> >>> +{
> >>> + if (x < (M << N) - GAP)
> >>> + return 0;
> >>> + UINT a = x - (M << N);
> >>> + UINT b = a >> N;
> >>> + return b + M;
> >>> +}
> >>> +
> >>> +UINT NOINLINE
> >>> +opt_u4 (UINT x)
> >>> +{
> >>> + if (x > (UMAX - (M << N)) + GAP)
> >>> + return 0;
> >>> + UINT a = x + (M << N);
> >>> + UINT b = a >> N;
> >>> + return b - M;
> >>> +}
> >>> +
> >>> +INT NOINLINE
> >>> +opt_s9 (INT x)
> >>> +{
> >>> + if (x < (M << N) - GAP)
> >>> + return 0;
> >>> + INT a = x - (M << N);
> >>> + INT b = a >> N;
> >>> + return b + M;
> >>> +}
> >>> +
> >>> +INT NOINLINE
> >>> +opt_s10 (INT x)
> >>> +{
> >>> + if (x < IMIN + (M << N) - GAP || x > 0)
> >>> + return 0;
> >>> + INT a = x - (M << N);
> >>> + INT b = a >> N;
> >>> + return b + M;
> >>> +}
> >>> +
> >>> +INT NOINLINE
> >>> +opt_s11 (INT x)
> >>> +{
> >>> + if (x > (-M << N) + GAP)
> >>> + return 0;
> >>> + INT a = x - (-M << N);
> >>> + INT b = a >> N;
> >>> + return b + -M;
> >>> +}
> >>> +
> >>> +INT NOINLINE
> >>> +opt_s12 (INT x)
> >>> +{
> >>> + if (x > IMAX - (M << N) + GAP || x < 0)
> >>> + return 0;
> >>> + INT a = x - (-M << N);
> >>> + INT b = a >> N;
> >>> + return b + -M;
> >>> +}
> >>>
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg,
Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman;
HRB 36809 (AG Nuernberg)
