[Bug middle-end/99407] New: s243 benchmark of TSVC is vectorized by clang and not by gcc

[Bug middle-end/99407] New: s243 benchmark of TSVC is vectorized by clang and not by gcc

[hubicka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99407

            Bug ID: 99407
           Summary: s243 benchmark of TSVC is vectorized by clang and not
                    by gcc
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hubicka at gcc dot gnu.org
  Target Milestone: ---

This testcase (from TSVC) is about 4 times faster on zen3 when built with
clang.

typedef float real_t;

#define iterations 100000
#define LEN_1D 32000
#define LEN_2D 256
// array definitions
real_t flat_2d_array[LEN_2D*LEN_2D];

real_t x[LEN_1D];

real_t a[LEN_1D],b[LEN_1D],c[LEN_1D],d[LEN_1D],e[LEN_1D],
bb[LEN_2D][LEN_2D],cc[LEN_2D][LEN_2D],tt[LEN_2D][LEN_2D];

int indx[LEN_1D];

real_t* __restrict__ xx;
real_t* yy;
real_t s243(void)
{

//    node splitting
//    false dependence cycle breaking

    for (int nl = 0; nl < iterations; nl++) {
        for (int i = 0; i < LEN_1D-1; i++) {
            a[i] = b[i] + c[i  ] * d[i];
            b[i] = a[i] + d[i  ] * e[i];
            a[i] = b[i] + a[i+1] * d[i];
        }
    }
}

internal loop from clang is:
.LBB0_2:                                #   Parent Loop BB0_1 Depth=1
                                        # =>  This Inner Loop Header: Depth=2
        vmovups c(%rcx), %ymm12
        vmovups c+32(%rcx), %ymm14
        vmovups d(%rcx), %ymm0
        vmovups d+32(%rcx), %ymm7
        vfmadd213ps     b(%rcx), %ymm0, %ymm12  # ymm12 = (ymm0 * ymm12) + mem
        vfmadd213ps     b+32(%rcx), %ymm7, %ymm14 # ymm14 = (ymm7 * ymm14) +
mem
        vfmadd231ps     e(%rcx), %ymm0, %ymm12  # ymm12 = (ymm0 * mem) + ymm12
        vfmadd231ps     e+32(%rcx), %ymm7, %ymm14 # ymm14 = (ymm7 * mem) +
ymm14
        vmovups %ymm12, b(%rcx)
        vmovups %ymm14, b+32(%rcx)
        vfmadd231ps     a+4(%rcx), %ymm0, %ymm12 # ymm12 = (ymm0 * mem) + ymm12
        vfmadd231ps     a+36(%rcx), %ymm7, %ymm14 # ymm14 = (ymm7 * mem) +
ymm14
        vmovups %ymm12, a(%rcx)
        vmovups %ymm14, a+32(%rcx)
        addq    $64, %rcx
        cmpq    $127936, %rcx                   # imm = 0x1F3C0
        jne     .LBB0_2

[Bug middle-end/99407] s243 benchmark of TSVC is vectorized by clang and not by gcc

[hubicka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99407

--- Comment #1 from Jan Hubicka <hubicka at gcc dot gnu.org> ---
Here we get:
s243.c:27:18: missed:   not vectorized, possible dependence between data-refs
a[i_29] and a[_9]
s243.c:26:27: missed:  bad data dependence.
s243.c:26:27: note:  ***** Analysis failed with vector mode V8QI

  <bb 6> [local count: 1052266997]:

  <bb 3> [local count: 1063004410]:
  # i_29 = PHI <_9(6), 0(4)>
  # ivtmp_43 = PHI <ivtmp_42(6), 31999(4)>
  _1 = b[i_29];
  _2 = c[i_29];
  _3 = d[i_29];
  _4 = _2 * _3;
  _5 = _1 + _4;
  a[i_29] = _5;
  _6 = e[i_29];
  _7 = _3 * _6;
  _8 = _5 + _7;
  b[i_29] = _8;
  _9 = i_29 + 1;
  _10 = a[_9];
  _11 = _3 * _10;
  _12 = _8 + _11;
  a[i_29] = _12;
  ivtmp_42 = ivtmp_43 - 1;
  if (ivtmp_42 != 0)
    goto <bb 6>; [98.99%]
  else
    goto <bb 5>; [1.01%]

[Bug tree-optimization/99407] s243 benchmark of TSVC is vectorized by clang and not by gcc, missed DSE

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99407

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2021-03-08
     Ever confirmed|0                           |1
           Keywords|                            |missed-optimization
             Blocks|                            |53947
            Summary|s243 benchmark of TSVC is   |s243 benchmark of TSVC is
                   |vectorized by clang and not |vectorized by clang and not
                   |by gcc                      |by gcc, missed DSE
          Component|middle-end                  |tree-optimization
             Status|UNCONFIRMED                 |NEW

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Hmm, wonder why DSE didn't remove the first a[i] store.  Ah, because DSE
doesn't use data-ref analysis and thus cannot disambiguate the variable offset.

Manually applying DSE produces

.L4:
        vmovaps c(%rax), %ymm1
        vaddps  e(%rax), %ymm1, %ymm0
        addq    $32, %rax
        vmovups a-28(%rax), %ymm1
        vmulps  d-32(%rax), %ymm1, %ymm1
        vmulps  d-32(%rax), %ymm0, %ymm0
        vaddps  b-32(%rax), %ymm0, %ymm0
        vmovaps %ymm0, b-32(%rax)
        vaddps  %ymm0, %ymm1, %ymm0
        vmovaps %ymm0, a-32(%rax)
        cmpq    $127968, %rax
        jne     .L4


manually DSEd loop:

    for (int nl = 0; nl < iterations; nl++) {
        for (int i = 0; i < LEN_1D-1; i++) {
            real_t tem = b[i] + c[i  ] * d[i];
            b[i] = tem + d[i  ] * e[i];
            a[i] = b[i] + a[i+1] * d[i];
        }
    }


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53947
[Bug 53947] [meta-bug] vectorizer missed-optimizations

[Bug tree-optimization/99407] s243 benchmark of TSVC is vectorized by clang and not by gcc, missed DSE

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99407

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Richard Biener <rguenth@gcc.gnu.org>:

https://gcc.gnu.org/g:4bdf739f835520ccbc433dc9eac461895741f317

commit r13-2769-g4bdf739f835520ccbc433dc9eac461895741f317
Author: Richard Biener <rguenther@suse.de>
Date:   Thu Sep 22 09:40:40 2022 +0200

    tree-optimization/99407 - DSE with data-ref analysis

    The following resolves the issue that DSE cannot handle references
    with variable offsets well when identifying possible uses of a store.
    Instead of just relying on ref_maybe_used_by_stmt_p we use data-ref
    analysis, making sure to perform that at most once per stmt.  The
    new mode is only exercised by the DSE pass before loop optimization
    as specified by a new pass parameter and when expensive optimizations
    are enabled, so it's disabled below -O2.

            PR tree-optimization/99407
            * tree-ssa-dse.cc (dse_stmt_to_dr_map): New global.
            (dse_classify_store): Use data-ref analysis to disambiguate more
uses.
            (pass_dse::use_dr_analysis_p): New pass parameter.
            (pass_dse::set_pass_param): Implement.
            (pass_dse::execute): Allocate and deallocate dse_stmt_to_dr_map.
            * passes.def: Allow DR analysis for the DSE pass before loop.

            * gcc.dg/vect/tsvc/vect-tsvc-s243.c: Remove XFAIL.

[Bug tree-optimization/99407] s243 benchmark of TSVC is vectorized by clang and not by gcc, missed DSE

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99407

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
      Known to work|                            |13.0
             Status|NEW                         |RESOLVED

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
Fixed for GCC 13.

[Bug tree-optimization/99407] s243 benchmark of TSVC is vectorized by clang and not by gcc, missed DSE

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99407

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |juzhe.zhong at rivai dot ai

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 106989 has been marked as a duplicate of this bug. ***

[Bug tree-optimization/99407] s243 benchmark of TSVC is vectorized by clang and not by gcc, missed DSE

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99407

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |13.0