[Bug 89970] i965/fs: copy propagate should propagate bitwise not into logic operations

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=89970

--- Comment #5 from Ian Romanick <idr at freedesktop.org> ---
(In reply to Ian Romanick from comment #4)
> At the time, we generated intBitsToFloat(b & floatBitsToInt(1.0)) to do b2f
> conversions.  Since b could only be 0 or -1, ~b & 0x38f00000 produces the
> same possible values as -b & 0x37f00000.  However, we now emit float(-b)
> instead, so I don't think this can occur anymore.
> 
> Maybe generating ~b & 0x3f800000 (BDW+) or -b & 0x38f00000 (SNB - HSW) for
> float(!b) is better?  Right now there's a late optimization in
> nir_opt_algebraic that does this:
> 
>    (('b2f(is_used_more_than_once)', ('inot', a)), ('bcsel', a, 0.0, 1.0)),
>    (('fneg(is_used_more_than_once)', ('b2f', ('inot', a))), ('bcsel', a,
> -0.0, -1.0)),
> 
> In at least some cases, this results in some extra load-immediate
> instructions
> 
> mov(16)         g16<1>D         1065353216D
> mov.nz.f0(16)   null<1>D        g8<8,8,1>D
> (-f0) sel(16)   g126<1>UD       g16<8,8,1>UD    0x00000000UD
> 
> Which also seems dumb.  This should be
> 
> mov.z.f0(16)    null<1>D        g8<8,8,1>D
> (-f0) sel(16)   g126<1>F        g8<8,8,1>F     1.0F

Ignore this last part.  That's rubbish.

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