i965/fs: Enumerate logical fb writes arguments

Gen9 adds the ability to write out a stencil value, so we need to expand the
virtual payload by one. Abstracting this now makes that change easier to read.

I was admittedly confused early on about some of the hardcoding. If people
believe the resulting code is inferior, I am not super attached to the patch.

v2:
Remove explicit numbering from the enumeration (Matt).
Use a real naming scheme, and reference it in the opcode definition (Curro)
Add a missed hardcoded logical position in get_lowered_simd_width (Ben)
Add an assertion to make sure the component numbering is correct (Ben)

Cc: Matt Turner <mattst88@gmail.com>
Cc: Francisco Jerez <currojerez@riseup.net>
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

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

@@ -911,15 +911,9 @@ enum opcode {
 
    /**
     * Same as FS_OPCODE_FB_WRITE but expects its arguments separately as
-    * individual sources instead of as a single payload blob:
-    *
-    * Source 0: [required] Color 0.
-    * Source 1: [optional] Color 1 (for dual source blend messages).
-    * Source 2: [optional] Src0 Alpha.
-    * Source 3: [optional] Source Depth (gl_FragDepth)
-    * Source 4: [optional (gen4-5)] Destination Depth passthrough from thread
-    * Source 5: [optional] Sample Mask (gl_SampleMask).
-    * Source 6: [required] Number of color components (as a UD immediate).
+    * individual sources instead of as a single payload blob. The
+    * position/ordering of the arguments are defined by the enum
+    * fb_write_logical_srcs.
     */
    FS_OPCODE_FB_WRITE_LOGICAL,
 
@@ -1330,6 +1324,16 @@ enum brw_urb_write_flags {
       BRW_URB_WRITE_ALLOCATE | BRW_URB_WRITE_COMPLETE,
 };
 
+enum fb_write_logical_srcs {
+   FB_WRITE_LOGICAL_SRC_COLOR0,      /* REQUIRED */
+   FB_WRITE_LOGICAL_SRC_COLOR1,      /* for dual source blend messages */
+   FB_WRITE_LOGICAL_SRC_SRC0_ALPHA,
+   FB_WRITE_LOGICAL_SRC_SRC_DEPTH,   /* gl_FragDepth */
+   FB_WRITE_LOGICAL_SRC_DST_DEPTH,   /* GEN4-5: passthrough from thread */
+   FB_WRITE_LOGICAL_SRC_OMASK,       /* Sample Mask (gl_SampleMask) */
+   FB_WRITE_LOGICAL_SRC_COMPONENTS,  /* REQUIRED */
+};
+
 #ifdef __cplusplus
 /**
  * Allow brw_urb_write_flags enums to be ORed together.

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

@@ -699,10 +699,10 @@ fs_inst::components_read(unsigned i) const
       return 2;
 
    case FS_OPCODE_FB_WRITE_LOGICAL:
-      assert(src[6].file == IMM);
+      assert(src[FB_WRITE_LOGICAL_SRC_COMPONENTS].file == IMM);
       /* First/second FB write color. */
       if (i < 2)
-         return src[6].fixed_hw_reg.dw1.ud;
+         return src[FB_WRITE_LOGICAL_SRC_COMPONENTS].fixed_hw_reg.dw1.ud;
       else
          return 1;
 
@@ -3350,15 +3350,16 @@ lower_fb_write_logical_send(const fs_builder &bld, fs_inst *inst,
                             const brw_wm_prog_key *key,
                             const fs_visitor::thread_payload &payload)
 {
-   assert(inst->src[6].file == IMM);
+   assert(inst->src[FB_WRITE_LOGICAL_SRC_COMPONENTS].file == IMM);
    const brw_device_info *devinfo = bld.shader->devinfo;
-   const fs_reg &color0 = inst->src[0];
-   const fs_reg &color1 = inst->src[1];
-   const fs_reg &src0_alpha = inst->src[2];
-   const fs_reg &src_depth = inst->src[3];
-   const fs_reg &dst_depth = inst->src[4];
-   fs_reg sample_mask = inst->src[5];
-   const unsigned components = inst->src[6].fixed_hw_reg.dw1.ud;
+   const fs_reg &color0 = inst->src[FB_WRITE_LOGICAL_SRC_COLOR0];
+   const fs_reg &color1 = inst->src[FB_WRITE_LOGICAL_SRC_COLOR1];
+   const fs_reg &src0_alpha = inst->src[FB_WRITE_LOGICAL_SRC_SRC0_ALPHA];
+   const fs_reg &src_depth = inst->src[FB_WRITE_LOGICAL_SRC_SRC_DEPTH];
+   const fs_reg &dst_depth = inst->src[FB_WRITE_LOGICAL_SRC_DST_DEPTH];
+   fs_reg sample_mask = inst->src[FB_WRITE_LOGICAL_SRC_OMASK];
+   const unsigned components =
+      inst->src[FB_WRITE_LOGICAL_SRC_COMPONENTS].fixed_hw_reg.dw1.ud;
 
    /* We can potentially have a message length of up to 15, so we have to set
     * base_mrf to either 0 or 1 in order to fit in m0..m15.
@@ -4186,10 +4187,12 @@ get_lowered_simd_width(const struct brw_device_info *devinfo,
       /* Gen6 doesn't support SIMD16 depth writes but we cannot handle them
        * here.
        */
-      assert(devinfo->gen != 6 || inst->src[3].file == BAD_FILE ||
+      assert(devinfo->gen != 6 ||
+             inst->src[FB_WRITE_LOGICAL_SRC_SRC_DEPTH].file == BAD_FILE ||
              inst->exec_size == 8);
       /* Dual-source FB writes are unsupported in SIMD16 mode. */
-      return (inst->src[1].file != BAD_FILE ? 8 : inst->exec_size);
+      return (inst->src[FB_WRITE_LOGICAL_SRC_COLOR1].file != BAD_FILE ?
+              8 : inst->exec_size);
 
    case SHADER_OPCODE_TXD_LOGICAL:
       /* TXD is unsupported in SIMD16 mode. */

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

@@ -710,6 +710,7 @@ fs_visitor::emit_single_fb_write(const fs_builder &bld,
       color0, color1, src0_alpha, src_depth, dst_depth, sample_mask,
       fs_reg(components)
    };
+   assert(ARRAY_SIZE(sources) - 1 == FB_WRITE_LOGICAL_SRC_COMPONENTS);
    fs_inst *write = bld.emit(FS_OPCODE_FB_WRITE_LOGICAL, fs_reg(),
                              sources, ARRAY_SIZE(sources));