On Sun, Oct 11, 2015 at 9:25 PM, Matt Turner <matts...@gmail.com> wrote: > On Sun, Oct 11, 2015 at 5:26 PM, Ilia Mirkin <imir...@alum.mit.edu> wrote: >> On Sat, Oct 10, 2015 at 1:17 PM, Matt Turner <matts...@gmail.com> wrote: >>> Curro added this in commit 3ee2daf23d (before the vec4/NIR backend was >>> added) but it was missed in the new NIR backend. Add it there as well. >>> >>> instructions in affected programs: 1857 -> 1810 (-2.53%) >>> helped: 15 >>> --- >>> src/mesa/drivers/dri/i965/brw_vec4_nir.cpp | 8 +------- >>> 1 file changed, 1 insertion(+), 7 deletions(-) >>> >>> diff --git a/src/mesa/drivers/dri/i965/brw_vec4_nir.cpp >>> b/src/mesa/drivers/dri/i965/brw_vec4_nir.cpp >>> index 41bd80d..fdf767d 100644 >>> --- a/src/mesa/drivers/dri/i965/brw_vec4_nir.cpp >>> +++ b/src/mesa/drivers/dri/i965/brw_vec4_nir.cpp >>> @@ -1237,14 +1237,8 @@ vec4_visitor::nir_emit_alu(nir_alu_instr *instr) >>> break; >>> >>> case nir_op_b2i: >>> - emit(AND(dst, op[0], src_reg(1))); >>> - break; >>> - >>> case nir_op_b2f: >>> - op[0].type = BRW_REGISTER_TYPE_D; >>> - dst.type = BRW_REGISTER_TYPE_D; >>> - emit(AND(dst, op[0], src_reg(0x3f800000u))); >>> - dst.type = BRW_REGISTER_TYPE_F; >>> + emit(MOV(dst, negate(op[0]))); >> >> For my own edification, could you explain how this works? Let's say >> you have a sequence like... >> >> bool b = ...; /* b contains 0 or ~0 "internally" */ >> int x = floatBitsToInt((float)b) + 1; > > b2f generates a type-converting MOV: mov dst:F, -src0:D.
Aha, this is the bit that I was missing. That makes sense then. > > Input of 0 is 0 negated, and 0.0f. Input of ~0 (-1) is 1 negated, and 1.0f. > > Your sequence would generate > > mov r0:F, -r1:D > add r2:D, r0:D, 1 > > and copy propagation won't mess things up because it only operates on > mixed-types in known-safe cases. > > (I haven't confirmed this) If that were broken, probably a lot more things would be broken. -ilia _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
