[Mesa-dev] [PATCH] i965/vec4: Don't disable channels in any/all comparisons.

[Matt Turner]

We've made a mistake in calling the Channel Enable bits "writemask",
because they do more than control which channels of the destination are
written -- they actually control which channels are enabled (surprise!
surprise!)

So, if we emit

               cmp.z.f0(8) null.xy<1>D  g10<4,4,1>.xyzzD g2<0,4,1>.xyzzD
               mov(8)      g12<1>.xUD   0x00000000UD
   (+f0.all4h) mov(8)      g12<1>.xUD   0xffffffffUD

where the CMP instruction has only .xy channel enables, it won't write
the .zw channels of the flag register, which are of course read by the
+f0.all4 predicate.

We need to always emit CMP instructions whose flag result might be read
by such a predicate with all channels enabled.
---
 src/mesa/drivers/dri/i965/brw_vec4_nir.cpp | 52 ++++++------------------------
 1 file changed, 10 insertions(+), 42 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_vec4_nir.cpp b/src/mesa/drivers/dri/i965/brw_vec4_nir.cpp
index 0f04f65..33cc02e 100644
--- a/src/mesa/drivers/dri/i965/brw_vec4_nir.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4_nir.cpp
@@ -1146,26 +1146,10 @@ vec4_visitor::nir_emit_alu(nir_alu_instr *instr)
    case nir_op_ball_iequal3:
    case nir_op_ball_fequal4:
    case nir_op_ball_iequal4: {
-      dst_reg tmp = dst_reg(this, glsl_type::bool_type);
+      unsigned swiz =
+         brw_swizzle_for_size(nir_op_infos[instr->op].input_sizes[0]);
 
-      switch (instr->op) {
-      case nir_op_ball_fequal2:
-      case nir_op_ball_iequal2:
-         tmp.writemask = WRITEMASK_XY;
-         break;
-      case nir_op_ball_fequal3:
-      case nir_op_ball_iequal3:
-         tmp.writemask = WRITEMASK_XYZ;
-         break;
-      case nir_op_ball_fequal4:
-      case nir_op_ball_iequal4:
-         tmp.writemask = WRITEMASK_XYZW;
-         break;
-      default:
-         unreachable("not reached");
-      }
-
-      emit(CMP(tmp, op[0], op[1],
+      emit(CMP(dst_null_d(), swizzle(op[0], swiz), swizzle(op[1], swiz),
                brw_conditional_for_nir_comparison(instr->op)));
       emit(MOV(dst, src_reg(0)));
       inst = emit(MOV(dst, src_reg(~0)));
@@ -1179,26 +1163,10 @@ vec4_visitor::nir_emit_alu(nir_alu_instr *instr)
    case nir_op_bany_inequal3:
    case nir_op_bany_fnequal4:
    case nir_op_bany_inequal4: {
-      dst_reg tmp = dst_reg(this, glsl_type::bool_type);
+      unsigned swiz =
+         brw_swizzle_for_size(nir_op_infos[instr->op].input_sizes[0]);
 
-      switch (instr->op) {
-      case nir_op_bany_fnequal2:
-      case nir_op_bany_inequal2:
-         tmp.writemask = WRITEMASK_XY;
-         break;
-      case nir_op_bany_fnequal3:
-      case nir_op_bany_inequal3:
-         tmp.writemask = WRITEMASK_XYZ;
-         break;
-      case nir_op_bany_fnequal4:
-      case nir_op_bany_inequal4:
-         tmp.writemask = WRITEMASK_XYZW;
-         break;
-      default:
-         unreachable("not reached");
-      }
-
-      emit(CMP(tmp, op[0], op[1],
+      emit(CMP(dst_null_d(), swizzle(op[0], swiz), swizzle(op[1], swiz),
                brw_conditional_for_nir_comparison(instr->op)));
 
       emit(MOV(dst, src_reg(0)));
@@ -1463,11 +1431,11 @@ vec4_visitor::nir_emit_alu(nir_alu_instr *instr)
    case nir_op_bany2:
    case nir_op_bany3:
    case nir_op_bany4: {
-      dst_reg tmp = dst_reg(this, glsl_type::bool_type);
-      tmp.writemask = brw_writemask_for_size(nir_op_infos[instr->op].input_sizes[0]);
-
-      emit(CMP(tmp, op[0], src_reg(0), BRW_CONDITIONAL_NZ));
+      unsigned swiz =
+         brw_swizzle_for_size(nir_op_infos[instr->op].input_sizes[0]);
 
+      emit(CMP(dst_null_d(), swizzle(op[0], swiz), src_reg(0),
+               BRW_CONDITIONAL_NZ));
       emit(MOV(dst, src_reg(0)));
       inst = emit(MOV(dst, src_reg(~0)));
       inst->predicate = BRW_PREDICATE_ALIGN16_ANY4H;
-- 
2.4.9