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?
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;
>> +}
>>
