[Mesa-dev] [PATCH] i965/fs: Fix 32-bit integer multiplication.

[Eric Anholt]

The MUL opcode does a 16bit * 32bit multiply, and we need to do the
MACH to get the top 16bit * 32bit added in.

Fixes fs-op-mult-int-*, fs-op-mult-ivec*
---
 src/mesa/drivers/dri/i965/brw_fs_emit.cpp    |    5 +++++
 src/mesa/drivers/dri/i965/brw_fs_visitor.cpp |   18 +++++++++++++++++-
 2 files changed, 22 insertions(+), 1 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_fs_emit.cpp b/src/mesa/drivers/dri/i965/brw_fs_emit.cpp
index e168e54..0a4b236 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_emit.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_emit.cpp
@@ -655,6 +655,11 @@ fs_visitor::generate_code()
       case BRW_OPCODE_MUL:
 	 brw_MUL(p, dst, src[0], src[1]);
 	 break;
+      case BRW_OPCODE_MACH:
+	 brw_set_acc_write_control(p, 1);
+	 brw_MACH(p, dst, src[0], src[1]);
+	 brw_set_acc_write_control(p, 0);
+	 break;
 
       case BRW_OPCODE_FRC:
 	 brw_FRC(p, dst, src[0]);
diff --git a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
index 2e3f9be..13ff840 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
@@ -287,7 +287,23 @@ fs_visitor::visit(ir_expression *ir)
       break;
 
    case ir_binop_mul:
-      emit(BRW_OPCODE_MUL, this->result, op[0], op[1]);
+      if (ir->type->is_integer()) {
+	 /* For integer multiplication, the MUL uses the low 16 bits
+	  * of one of the operands (src0 on gen6, src1 on gen7).  The
+	  * MACH accumulates in the contribution of the upper 16 bits
+	  * of that operand.
+	  *
+	  * FINISHME: Emit just the MUL if we know an operand is small
+	  * enough.
+	  */
+	 struct brw_reg acc = retype(brw_acc_reg(), BRW_REGISTER_TYPE_D);
+
+	 emit(BRW_OPCODE_MUL, acc, op[0], op[1]);
+	 emit(BRW_OPCODE_MACH, reg_null_d, op[0], op[1]);
+	 emit(BRW_OPCODE_MOV, this->result, fs_reg(acc));
+      } else {
+	 emit(BRW_OPCODE_MUL, this->result, op[0], op[1]);
+      }
       break;
    case ir_binop_div:
       assert(!"not reached: should be handled by ir_div_to_mul_rcp");
-- 
1.7.5.4