i965: Define virtual instruction to calculate the high 32 bits of a multiply.

This instruction will translate to the MUL/MACH sequence that computes
the high 32-bits of the result of a 64-bit multiply.  Before Gen8
integer operations that used the accumulator were limited to 8-wide,
but the SIMD lowering pass can easily be hooked up to sidestep this
limitation, we just need a virtual opcode to represent the MUL/MACH
sequence in the IR.

Reviewed-by: Matt Turner <mattst88@gmail.com>

src/mesa/drivers/dri/i965/brw_defines.h

@@ -1214,6 +1214,11 @@ enum opcode {
     * GLSL barrier()
     */
    SHADER_OPCODE_BARRIER,
+
+   /**
+    * Calculate the high 32-bits of a 32x32 multiply.
+    */
+   SHADER_OPCODE_MULH,
 };
 
 enum brw_urb_write_flags {

src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp

@@ -534,6 +534,7 @@ fs_visitor::try_constant_propagate(fs_inst *inst, acp_entry *entry)
 
       case BRW_OPCODE_MACH:
       case BRW_OPCODE_MUL:
+      case SHADER_OPCODE_MULH:
       case BRW_OPCODE_ADD:
       case BRW_OPCODE_OR:
       case BRW_OPCODE_AND:

src/mesa/drivers/dri/i965/brw_fs_cse.cpp

@@ -61,6 +61,7 @@ is_expression(const fs_visitor *v, const fs_inst *const inst)
    case BRW_OPCODE_CMPN:
    case BRW_OPCODE_ADD:
    case BRW_OPCODE_MUL:
+   case SHADER_OPCODE_MULH:
    case BRW_OPCODE_FRC:
    case BRW_OPCODE_RNDU:
    case BRW_OPCODE_RNDD:

src/mesa/drivers/dri/i965/brw_shader.cpp

@@ -778,6 +778,8 @@ brw_instruction_name(enum opcode op)
       return "cs_terminate";
    case SHADER_OPCODE_BARRIER:
       return "barrier";
+   case SHADER_OPCODE_MULH:
+      return "mulh";
    }
 
    unreachable("not reached");
@@ -996,6 +998,7 @@ backend_instruction::is_commutative() const
    case BRW_OPCODE_XOR:
    case BRW_OPCODE_ADD:
    case BRW_OPCODE_MUL:
+   case SHADER_OPCODE_MULH:
       return true;
    case BRW_OPCODE_SEL:
       /* MIN and MAX are commutative. */
@@ -1103,6 +1106,7 @@ backend_instruction::can_do_saturate() const
    case BRW_OPCODE_MATH:
    case BRW_OPCODE_MOV:
    case BRW_OPCODE_MUL:
+   case SHADER_OPCODE_MULH:
    case BRW_OPCODE_PLN:
    case BRW_OPCODE_RNDD:
    case BRW_OPCODE_RNDE:

src/mesa/drivers/dri/i965/brw_vec4_copy_propagation.cpp

@@ -179,6 +179,7 @@ try_constant_propagate(const struct brw_device_info *devinfo,
 
    case BRW_OPCODE_MACH:
    case BRW_OPCODE_MUL:
+   case SHADER_OPCODE_MULH:
    case BRW_OPCODE_ADD:
    case BRW_OPCODE_OR:
    case BRW_OPCODE_AND:

src/mesa/drivers/dri/i965/brw_vec4_cse.cpp

@@ -62,6 +62,7 @@ is_expression(const vec4_instruction *const inst)
    case BRW_OPCODE_CMPN:
    case BRW_OPCODE_ADD:
    case BRW_OPCODE_MUL:
+   case SHADER_OPCODE_MULH:
    case BRW_OPCODE_FRC:
    case BRW_OPCODE_RNDU:
    case BRW_OPCODE_RNDD: