glsl: Hard-code noise to zero in builtin_functions.cpp

Version 4.4 of the GLSL spec changed the definition of noise*() to
always return zero and earlier versions of the spec allowed zero as a
valid implementation.

All drivers, as far as I can tell, unconditionally call lower_noise()
today which turns ir_unop_noise into zero.  We've got a 10-year-old
comment in there saying "In the future, ir_unop_noise may be replaced by
a call to a function that implements noise."  Well, it's the future now
and we've not yet gotten around to that.  In the mean time, the GLSL
spec has made doing so illegal.

To make things worse, we then pretend to handle the opcode in
glsl_to_nir, ir_to_mesa, and st_glsl_to_tgsi even though it should never
get there given the lowering.  The lowering in st_glsl_to_tgsi defines
noise*() to be 0.5 which is an illegal implementation of the noise
functions according to pre-4.4 specs.  We also have opcodes for this in
NIR which are never used because, again, we always call lower_noise().

Let's just kill the whole opcode and make builtin_builder.cpp build a
bunch of functions that just return zero.

Reviewed-by: Alyssa Rosenzweig <[email protected]>
Reviewed-by: Kenneth Graunke <[email protected]>
Reviewed-by: Eric Anholt <[email protected]>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4624>

4 files changed, 0 insertions, 24 deletions

diff --git a/src/mesa/drivers/dri/i965/brw_link.cpp b/src/mesa/drivers/dri/i965/brw_link.cpp
index 67e4a36103f..cfd56cef0df 100644
--- a/src/mesa/drivers/dri/i965/brw_link.cpp
+++ b/src/mesa/drivers/dri/i965/brw_link.cpp
@@ -135,7 +135,6 @@ process_glsl_ir(struct brw_context *brw,
    do_vec_index_to_cond_assign(shader->ir);
    lower_vector_insert(shader->ir, true);
    lower_offset_arrays(shader->ir);
-   lower_noise(shader->ir);
    lower_quadop_vector(shader->ir, false);
 
    validate_ir_tree(shader->ir);
diff --git a/src/mesa/program/ir_to_mesa.cpp b/src/mesa/program/ir_to_mesa.cpp
index adb8720c622..3b8472384ca 100644
--- a/src/mesa/program/ir_to_mesa.cpp
+++ b/src/mesa/program/ir_to_mesa.cpp
@@ -1030,15 +1030,6 @@ ir_to_mesa_visitor::visit(ir_expression *ir)
       inst->saturate = true;
       break;
    }
-   case ir_unop_noise: {
-      const enum prog_opcode opcode =
-	 prog_opcode(OPCODE_NOISE1
-		     + (ir->operands[0]->type->vector_elements) - 1);
-      assert((opcode >= OPCODE_NOISE1) && (opcode <= OPCODE_NOISE4));
-
-      emit(ir, opcode, result_dst, op[0]);
-      break;
-   }
 
    case ir_binop_add:
       emit(ir, OPCODE_ADD, result_dst, op[0], op[1]);
@@ -3022,8 +3013,6 @@ _mesa_ir_link_shader(struct gl_context *ctx, struct gl_shader_program *prog)
 	 progress = lower_if_to_cond_assign((gl_shader_stage)i, ir,
                                             options->MaxIfDepth) || progress;
 
-         progress = lower_noise(ir) || progress;
-
 	 /* If there are forms of indirect addressing that the driver
 	  * cannot handle, perform the lowering pass.
 	  */
diff --git a/src/mesa/state_tracker/st_glsl_to_ir.cpp b/src/mesa/state_tracker/st_glsl_to_ir.cpp
index 4d2a45728a9..e450fec6d99 100644
--- a/src/mesa/state_tracker/st_glsl_to_ir.cpp
+++ b/src/mesa/state_tracker/st_glsl_to_ir.cpp
@@ -159,7 +159,6 @@ st_link_shader(struct gl_context *ctx, struct gl_shader_program *prog)
       do_vec_index_to_cond_assign(ir);
       lower_vector_insert(ir, true);
       lower_quadop_vector(ir, false);
-      lower_noise(ir);
       if (options->MaxIfDepth == 0) {
          lower_discard(ir);
       }
diff --git a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
index a9a824f7bda..8eb0dda9fae 100644
--- a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
+++ b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
@@ -1572,17 +1572,6 @@ glsl_to_tgsi_visitor::visit_expression(ir_expression* ir, st_src_reg *op)
       emit_asm(ir, TGSI_OPCODE_DFRACEXP, undef_dst, result_dst, op[0]);
       break;
 
-   case ir_unop_noise: {
-      /* At some point, a motivated person could add a better
-       * implementation of noise.  Currently not even the nvidia
-       * binary drivers do anything more than this.  In any case, the
-       * place to do this is in the GL state tracker, not the poor
-       * driver.
-       */
-      emit_asm(ir, TGSI_OPCODE_MOV, result_dst, st_src_reg_for_float(0.5));
-      break;
-   }
-
    case ir_binop_add:
       emit_asm(ir, TGSI_OPCODE_ADD, result_dst, op[0], op[1]);
       break;