i965/fs: Add support for generating MADs.

Improves nexuiz performance 0.65% +/- .10% (n=5) on my gen6, and .39%
+/- .11% (n=10) on gen7.  No statistically significant performance
difference on warsow (n=5, but only one shader has MADs).

v2: Add support for MADs in 16-wide by using compression control.
v3: Don't generate MADs when it will force an immediate to be moved to a temp.
    (it's not clear whether this is a win or not, but it should result in less
     questionable change to codegen compared to v2).

Reviewed-by: Kenneth Graunke <[email protected]> (v2)

1 files changed, 41 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 ea8cd371786..e670ba79c18 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
@@ -182,6 +182,43 @@ fs_visitor::try_emit_saturate(ir_expression *ir)
    return true;
 }
 
+bool
+fs_visitor::try_emit_mad(ir_expression *ir, int mul_arg)
+{
+   /* 3-src instructions were introduced in gen6. */
+   if (intel->gen < 6)
+      return false;
+
+   /* MAD can only handle floating-point data. */
+   if (ir->type != glsl_type::float_type)
+      return false;
+
+   ir_rvalue *nonmul = ir->operands[1 - mul_arg];
+   ir_expression *mul = ir->operands[mul_arg]->as_expression();
+
+   if (!mul || mul->operation != ir_binop_mul)
+      return false;
+
+   if (nonmul->as_constant() ||
+       mul->operands[0]->as_constant() ||
+       mul->operands[1]->as_constant())
+      return false;
+
+   nonmul->accept(this);
+   fs_reg src0 = this->result;
+
+   mul->operands[0]->accept(this);
+   fs_reg src1 = this->result;
+
+   mul->operands[1]->accept(this);
+   fs_reg src2 = this->result;
+
+   this->result = fs_reg(this, ir->type);
+   emit(BRW_OPCODE_MAD, this->result, src0, src1, src2);
+
+   return true;
+}
+
 void
 fs_visitor::visit(ir_expression *ir)
 {
@@ -193,6 +230,10 @@ fs_visitor::visit(ir_expression *ir)
 
    if (try_emit_saturate(ir))
       return;
+   if (ir->operation == ir_binop_add) {
+      if (try_emit_mad(ir, 0) || try_emit_mad(ir, 1))
+	 return;
+   }
 
    for (operand = 0; operand < ir->get_num_operands(); operand++) {
       ir->operands[operand]->accept(this);