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. 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) _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
