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Date:	Thu, 03 Sep 1998 10:48:21 +0100
Date-warning:	Date header was inserted by risoe.dk
From:	Kristian Nielsen <kristian DOT nielsen AT risoe DOT dk>
Subject:	Found problem with -fpeep-spills in PGCC 2.90.29
To:	beastium-list AT Desk DOT nl
Message-id:	<01J1D87D9B928X38A4@risoe.dk>
MIME-version:	1.0 (generated by tm-edit 7.106)
Sender:	Marc Lehmann <pcg AT goof DOT com>
Status:	RO
Lines:	102

Hi,

I found a way to reproduce a problem with the -fpeep-spills optimization
in pgcc-2.90.29 980515 (egcs-1.0.3 release). The example is reasonably
short, and the assembler output with and without -fpeep-spills have
essentially only a single difference (an extra spill and reload without
-fpeep-spills), so I hope it will be useful to find the bug.

Compiled with

    gcc -O3 -o pgcc-bug-bad pgcc-bug.c -lm

the program below gives the (wrong) output

    Before: vy = 5
    After: vy = 1000

Compiled with

    gcc -O3 -fno-peep-spills -o pgcc-bug-ok pgcc-bug.c -lm

the program gives the (correct) output

    Before: vy = 5
    After: vy = 5

Program text and assembler output with and without -fpeep-spills are
also available via WWW on

    http://www.diku.dk/~bombadil/pgcc-bug.c
    http://www.diku.dk/~bombadil/pgcc-bug-bad.S
    http://www.diku.dk/~bombadil/pgcc-bug-ok.S

Hope this helps,

 - Kristian.

------------------------------------------------------------------------
typedef double MCNUM;
typedef struct {MCNUM x, y, z;} Coords;
typedef MCNUM Rotation[3][3];

/* Add two coordinates */
static Coords
coords_add(Coords a, Coords b)
{
  Coords c;

  c.x = a.x + b.x;
  c.y = a.y + b.y;
  c.z = a.z + b.z;
  return c;
}

/* Multiply matrix and corrdinate vector */
static Coords
rot_apply(Rotation t, Coords a)
{
  Coords b;

  b.x = t[0][0]*a.x + t[0][1]*a.y + t[0][2]*a.z;
  b.y = t[1][0]*a.x + t[1][1]*a.y + t[1][2]*a.z;
  b.z = t[2][0]*a.x + t[2][1]*a.y + t[2][2]*a.z;
  return b;
}

static void
mccoordschange(Coords a, Rotation t, double *x, double *y, double *z,
	       double *vx, double *vy, double *vz, double *time,
	       double *s1, double *s2)
{
  Coords b, c;

  b.x = *x;
  b.y = *y;
  b.z = *z;
  c = rot_apply(t, b);
  b = coords_add(c, a);
  *x = b.x;
  *y = b.y;
  *z = b.z;

  b.x = *vx;
  b.y = *vy;
  b.z = *vz;
  c = rot_apply(t, b);
  *vx = c.x;
  *vy = c.y;
  *vz = c.z;
}

Coords a = {0, 0, 1000};
Rotation t = { {1,0,0}, {0,1,0}, {0,0,1} };

main()
{
  double x = 10, y = 20, z = 0, vx = 3, vy = 5, vz = 50;
  double time = 0, s1 = 0, s2 = 0;
  printf("Before: vy = %g\n", vy);
  mccoordschange(a, t, &x, &y, &z, &vx, &vy, &vz, &time, &s1, &s2);
  printf("After: vy = %g\n", vy);
}

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