optimization/7426: unable to find a register to spill in class `FLOAT_REGS'

[gbeauchesne@mandrakesoft.com]

>Number:         7426
>Category:       optimization
>Synopsis:       unable to find a register to spill in class `FLOAT_REGS'
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Jul 28 14:36:00 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator:     Gwenole Beauchesne
>Release:        GNU C version 3.2 2002-07-26 (prerelease) (i686-pc-linux-gnu)
>Organization:
>Environment:
i686-mandrake-linux-gnu
>Description:
[gb@no gcc]$ ./cc1 -O -march=athlon ice.c 
 f
ice.c: In function `f':
ice.c:11: unable to find a register to spill in class `FLOAT_REGS'

ice.c:11: this is the insn:
(insn 18 52 23 (set (subreg:SF (reg/v:DI 29 rmm0 [59]) 0)
        (minus:SF (reg:SF 8 st(0) [62])
            (mem/j:SF (symbol_ref:SI ("pos")) [0 pos+0 S4 A32]))) 533 {*fop_sf_1_nosse} (insn_list 15 (nil))
    (expr_list:REG_DEAD (reg:SF 8 st(0) [62])
        (nil)))
ice.c:11: confused by earlier errors, bailing out
>How-To-Repeat:
Testcase extracted from <chromium>/src/EnemyAircraft_Omni.cpp (EnemyAircraft_Omni::move).

[gb@no gcc]$ cat ice.c 
float lastMoveX;
float pos[2];

extern void * target;

void f()
{
  float *hpos = pos;
  float diff[2] = { hpos[0] - pos[0], hpos[1] - pos[1] };
  lastMoveX = (0.9 * lastMoveX) + (0.1 * (0.01 * diff[0]));
}

Compile with -O -march=athlon to exhaust the bug. Likewise for any arch that has PTA_MMX flag but "pentium-mmx".
>Fix:
-march=i686 is OK.
>Release-Note:
>Audit-Trail:
>Unformatted: