i965/fs: Emit MADs from (x + -(y * z)).

Just use the negation source modifier on one of the multiplicand
arguments.

total instructions in shared programs: 5889529 -> 5880016 (-0.16%)
instructions in affected programs:     600846 -> 591333 (-1.58%)

Reviewed-by: Kristian Høgsberg <[email protected]>

1 files changed, 12 insertions, 0 deletions

diff --git a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
index 6ddb267cc19..7c062ec8abd 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
@@ -431,10 +431,21 @@ fs_visitor::try_emit_mad(ir_expression *ir)
    ir_rvalue *nonmul = ir->operands[1];
    ir_expression *mul = ir->operands[0]->as_expression();
 
+   bool mul_negate = false;
+   if (mul && mul->operation == ir_unop_neg) {
+      mul = mul->operands[0]->as_expression();
+      mul_negate = true;
+   }
+
    if (!mul || mul->operation != ir_binop_mul) {
       nonmul = ir->operands[0];
       mul = ir->operands[1]->as_expression();
 
+      if (mul && mul->operation == ir_unop_neg) {
+         mul = mul->operands[0]->as_expression();
+         mul_negate = true;
+      }
+
       if (!mul || mul->operation != ir_binop_mul)
          return false;
    }
@@ -449,6 +460,7 @@ fs_visitor::try_emit_mad(ir_expression *ir)
 
    mul->operands[0]->accept(this);
    fs_reg src1 = this->result;
+   src1.negate ^= mul_negate;
 
    mul->operands[1]->accept(this);
    fs_reg src2 = this->result;