intel/compiler: remove inexact algebraic optimizations from the backend

NIR already has these and correctly considers exact/inexact qualification,
whereas the backend doesn't and can apply the optimizations where it
shouldn't. This happened to be the case in a handful of Tomb Raider shaders,
where NIR would skip the optimizations because of a precise qualification
but the backend would then (incorrectly) apply them anyway.

Besides this, considering that we are not emitting much math in the backend
these days it is unlikely that these optimizations are useful in general. A
shader-db run confirms that MAD and LRP optimizations, for example, were only
being triggered in cases where NIR would skip them due to precise
requirements, so in the near future we might want to remove more of these,
but for now we just remove the ones that are not completely correct.

Suggested-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>

diff --git a/src/intel/compiler/brw_fs.cpp b/src/intel/compiler/brw_fs.cpp
index ebcdd52d668b5ce6d91d75fef668a4874cc92cbe..186275b32406510da42fd84561619b17e23316e4 100644 (file)
--- a/src/intel/compiler/brw_fs.cpp
+++ b/src/intel/compiler/brw_fs.cpp
@@ -2576,15 +2576,6 @@ fs_visitor::opt_algebraic()
             break;
          }
 
-         /* a * 0.0 = 0.0 */
-         if (inst->src[1].is_zero()) {
-            inst->opcode = BRW_OPCODE_MOV;
-            inst->src[0] = inst->src[1];
-            inst->src[1] = reg_undef;
-            progress = true;
-            break;
-         }
-
          if (inst->src[0].file == IMM) {
             assert(inst->src[0].type == BRW_REGISTER_TYPE_F);
             inst->opcode = BRW_OPCODE_MOV;
@@ -2598,14 +2589,6 @@ fs_visitor::opt_algebraic()
          if (inst->src[1].file != IMM)
             continue;
 
-         /* a + 0.0 = a */
-         if (inst->src[1].is_zero()) {
-            inst->opcode = BRW_OPCODE_MOV;
-            inst->src[1] = reg_undef;
-            progress = true;
-            break;
-         }
-
          if (inst->src[0].file == IMM) {
             assert(inst->src[0].type == BRW_REGISTER_TYPE_F);
             inst->opcode = BRW_OPCODE_MOV;
@@ -2633,16 +2616,6 @@ fs_visitor::opt_algebraic()
             break;
          }
          break;
-      case BRW_OPCODE_LRP:
-         if (inst->src[1].equals(inst->src[2])) {
-            inst->opcode = BRW_OPCODE_MOV;
-            inst->src[0] = inst->src[1];
-            inst->src[1] = reg_undef;
-            inst->src[2] = reg_undef;
-            progress = true;
-            break;
-         }
-         break;
       case BRW_OPCODE_CMP:
          if ((inst->conditional_mod == BRW_CONDITIONAL_Z ||
               inst->conditional_mod == BRW_CONDITIONAL_NZ) &&
@@ -2720,17 +2693,7 @@ fs_visitor::opt_algebraic()
          }
          break;
       case BRW_OPCODE_MAD:
-         if (inst->src[1].is_zero() || inst->src[2].is_zero()) {
-            inst->opcode = BRW_OPCODE_MOV;
-            inst->src[1] = reg_undef;
-            inst->src[2] = reg_undef;
-            progress = true;
-         } else if (inst->src[0].is_zero()) {
-            inst->opcode = BRW_OPCODE_MUL;
-            inst->src[0] = inst->src[2];
-            inst->src[2] = reg_undef;
-            progress = true;
-         } else if (inst->src[1].is_one()) {
+         if (inst->src[1].is_one()) {
             inst->opcode = BRW_OPCODE_ADD;
             inst->src[1] = inst->src[2];
             inst->src[2] = reg_undef;