i965/fs: Allow flipping cond mod for negated arguments.

This allows us to apply the optimization in cases where the CMP's
argument is negated, by flipping the conditional mod. For example, it
allows us to optimize this:

   add(8)       temp   a      b
   cmp.l.f0(8)  null   -temp  0.0

into

   add.g.f0(8)  temp   a      b

total instructions in shared programs: 5958360 -> 5955701 (-0.04%)
instructions in affected programs:     466880 -> 464221 (-0.57%)
GAINED:                                0
LOST:                                  1

Reviewed-by: Jason Ekstrand <jason.ekstrand@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

2 files changed, 39 insertions, 3 deletions

diff --git a/src/mesa/drivers/dri/i965/brw_fs_cmod_propagation.cpp b/src/mesa/drivers/dri/i965/brw_fs_cmod_propagation.cpp
index c8eb3a4..8a03315 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_cmod_propagation.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_cmod_propagation.cpp
@@ -62,7 +62,6 @@ opt_cmod_propagation_local(fs_visitor *v, bblock_t *block)
           !inst->dst.is_null() ||
           inst->src[0].file != GRF ||
           inst->src[0].abs ||
-          inst->src[0].negate ||
           !inst->src[1].is_zero())
          continue;
 
@@ -74,10 +73,14 @@ opt_cmod_propagation_local(fs_visitor *v, bblock_t *block)
                 scan_inst->dst.reg_offset != inst->src[0].reg_offset)
                break;
 
+            enum brw_conditional_mod cond =
+               inst->src[0].negate ? brw_swap_cmod(inst->conditional_mod)
+                                   : inst->conditional_mod;
+
             if (scan_inst->can_do_cmod() &&
                 ((!read_flag && scan_inst->conditional_mod == BRW_CONDITIONAL_NONE) ||
-                 scan_inst->conditional_mod == inst->conditional_mod)) {
-               scan_inst->conditional_mod = inst->conditional_mod;
+                 scan_inst->conditional_mod == cond)) {
+               scan_inst->conditional_mod = cond;
                inst->remove(block);
                progress = true;
             }
diff --git a/src/mesa/drivers/dri/i965/test_fs_cmod_propagation.cpp b/src/mesa/drivers/dri/i965/test_fs_cmod_propagation.cpp
index 95d335d..fefe515 100644
--- a/src/mesa/drivers/dri/i965/test_fs_cmod_propagation.cpp
+++ b/src/mesa/drivers/dri/i965/test_fs_cmod_propagation.cpp
@@ -350,3 +350,36 @@ TEST_F(cmod_propagation_test, intervening_flag_read_same_value)
    EXPECT_EQ(BRW_OPCODE_SEL, instruction(block0, 1)->opcode);
    EXPECT_EQ(BRW_PREDICATE_NORMAL, instruction(block0, 1)->predicate);
 }
+
+TEST_F(cmod_propagation_test, negate)
+{
+   fs_reg dest = v->vgrf(glsl_type::float_type);
+   fs_reg src0 = v->vgrf(glsl_type::float_type);
+   fs_reg src1 = v->vgrf(glsl_type::float_type);
+   fs_reg zero(0.0f);
+   v->emit(BRW_OPCODE_ADD, dest, src0, src1);
+   dest.negate = true;
+   v->emit(BRW_OPCODE_CMP, v->reg_null_f, dest, zero)
+      ->conditional_mod = BRW_CONDITIONAL_GE;
+
+   /* = Before =
+    *
+    * 0: add(8)        dest  src0  src1
+    * 1: cmp.ge.f0(8)  null  -dest 0.0f
+    *
+    * = After =
+    * 0: add.le.f0(8)  dest  src0  src1
+    */
+
+   v->calculate_cfg();
+   bblock_t *block0 = v->cfg->blocks[0];
+
+   EXPECT_EQ(0, block0->start_ip);
+   EXPECT_EQ(1, block0->end_ip);
+
+   EXPECT_TRUE(cmod_propagation(v));
+   EXPECT_EQ(0, block0->start_ip);
+   EXPECT_EQ(0, block0->end_ip);
+   EXPECT_EQ(BRW_OPCODE_ADD, instruction(block0, 0)->opcode);
+   EXPECT_EQ(BRW_CONDITIONAL_LE, instruction(block0, 0)->conditional_mod);
+}