[Bug tree-optimization/108844] New: sincos opportunity missed

[Bug tree-optimization/108844] New: sincos opportunity missed

[tkoenig at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108844

            Bug ID: 108844
           Summary: sincos opportunity missed
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tkoenig at gcc dot gnu.org
  Target Milestone: ---

Two related test cases (which do the same, but are handled differently).

This is code for calculating a Jacobian, a frequent task in solving
non-linear systems of equations.  (I am using C instead of Fortran because
Fortran does not support fallthrough).

$ cat a.c
#include <math.h>

void f1 (double x, double y, double f[2], double fjac[2][2], int flag)
{
  switch (flag)
    {
    case 1:
      f[0] = x * y;
      f[1] = sin(x)*y*y;
      break;
    case 2:
      fjac[0][0] = y;
      fjac[1][0] = cos(x)*y*y;
      fjac[0][1] = x;
      fjac[1][1] = 2*sin(x)*y;
      break;
    case 3:
      f[0] = x * y;
      f[1] = sin(x)*y*y;
      fjac[0][0] = y;
      fjac[1][0] = cos(x)*y*y;
      fjac[0][1] = x;
      fjac[1][1] = 2*sin(x)*y;
      break;
     default:
      __builtin_unreachable();
    }
}
$ cat b.c
#include <math.h>

void f1 (double x, double y, double f[2], double fjac[2][2], int flag)
{
  switch (flag)
    {
    case 1:
    case 3:
      f[0] = x * y;
      f[1] = sin(x)*y*y;
      if (flag != 3)
        break;
      /* Fallthrough */
    case 2:
      fjac[0][0] = y;
      fjac[1][0] = cos(x)*y*y;
      fjac[0][1] = x;
      fjac[1][1] = 2*sin(x)*y;
      break;
    default:
      __builtin_unreachable();
    }
}
$ gcc -O3 -S a.c b.c

a.s looks good for flag=3:
        leaq    64(%rsp), %rsi
        leaq    72(%rsp), %rdi
        movaps  %xmm3, 48(%rsp)
        movsd   %xmm1, 32(%rsp)
        movsd   %xmm0, 24(%rsp)
        call    sincos

but the code for flag=2 looks like

        cmpl    $2, %edx
        je      .L2
[...]
.L2:
        .cfi_restore_state
        movaps  %xmm3, 32(%rsp)
        movsd   %xmm1, 24(%rsp)
        movsd   %xmm0, (%rsp)
        call    cos
        movsd   (%rsp), %xmm2
        movq    %xmm0, %rbx
        movapd  %xmm2, %xmm0
        call    sin

b.s generates no call to sincos:
$ egrep  '(sin|cos)' b.s
        call    sin
        call    sin
        call    cos

[Bug tree-optimization/108844] sincos opportunity missed

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108844

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2023-02-20
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed.  Probably a algorithmic deficiency in the sincos pass which tries
to combine all sin/cos uses of a specific value but in this case would need
to combine them into two distinct sincos calls.