[Mesa-dev] [PATCH 2/2] i965: Optimize multiplication by -1 into a negated MOV.

[Matt Turner]

instructions in affected programs:     968 -> 942 (-2.69%)
helped:                                4
---
 src/mesa/drivers/dri/i965/brw_fs.cpp   | 9 +++++++++
 src/mesa/drivers/dri/i965/brw_vec4.cpp | 5 +++++
 2 files changed, 14 insertions(+)

diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
index e74a22e..988e36a 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
@@ -2335,6 +2335,15 @@ fs_visitor::opt_algebraic()
 	    break;
 	 }
 
+	 /* a * -1.0 = -a */
+	 if (inst->src[1].is_negative_one()) {
+	    inst->opcode = BRW_OPCODE_MOV;
+            inst->src[0].negate = !inst->src[0].negate;
+	    inst->src[1] = reg_undef;
+	    progress = true;
+	    break;
+	 }
+
          /* a * 0.0 = 0.0 */
          if (inst->src[1].is_zero()) {
             inst->opcode = BRW_OPCODE_MOV;
diff --git a/src/mesa/drivers/dri/i965/brw_vec4.cpp b/src/mesa/drivers/dri/i965/brw_vec4.cpp
index ee74052..7868465 100644
--- a/src/mesa/drivers/dri/i965/brw_vec4.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4.cpp
@@ -725,6 +725,11 @@ vec4_visitor::opt_algebraic()
 	    inst->opcode = BRW_OPCODE_MOV;
 	    inst->src[1] = src_reg();
 	    progress = true;
+	 } else if (inst->src[1].is_negative_one()) {
+	    inst->opcode = BRW_OPCODE_MOV;
+            inst->src[0].negate = !inst->src[0].negate;
+	    inst->src[1] = src_reg();
+	    progress = true;
 	 }
 	 break;
       case BRW_OPCODE_CMP:
-- 
2.0.5