cell: re-order the z/stencil fetch/extract/convert instructions for better perf

The new instruction order is 10 cycles faster.

1 files changed, 51 insertions, 55 deletions

diff --git a/src/gallium/drivers/cell/ppu/cell_gen_fragment.c b/src/gallium/drivers/cell/ppu/cell_gen_fragment.c
index 4d28d48..b3cce68 100644
--- a/src/gallium/drivers/cell/ppu/cell_gen_fragment.c
+++ b/src/gallium/drivers/cell/ppu/cell_gen_fragment.c
@@ -1813,93 +1813,88 @@ gen_depth_stencil(struct cell_context *cell,
    const enum pipe_format zs_format = cell->framebuffer.zsbuf->format;
    boolean write_depth_stencil;
 
-   /* We may or may not need to allocate a register for Z or stencil values */
-   int fbS_reg = -1, fbZ_reg = -1;
-
-   /* framebuffer's combined z/stencil values for quad */
+   /* framebuffer's combined z/stencil values register */
    int fbZS_reg = spe_allocate_available_register(f);
 
+   /* Framebufer Z values register */
+   int fbZ_reg = spe_allocate_available_register(f);
 
-   spe_comment(f, 0, "Fetch Z/stencil quad from tile");
+   /* Framebuffer stencil values register (may not be used) */
+   int fbS_reg = spe_allocate_available_register(f);
+
+   /* 24-bit mask register (may not be used) */
+   int zmask_reg = spe_allocate_available_register(f);
 
-   /* fetch quad of depth/stencil values from tile at (x,y) */
-   /* Load: fbZS_reg = memory[depth_tile_reg + offset_reg] */
-   /* XXX Not sure this is allowed if we've only got a 16-bit Z buffer... */
-   spe_lqx(f, fbZS_reg, depth_tile_reg, quad_offset_reg);
-
-   /* From the Z/stencil buffer format, pull out the bits we need for
-    * Z and/or stencil.  We'll also convert the incoming fragment Z
-    * value in fragZ_reg from a floating point value in [0.0..1.0] to
-    * an unsigned integer value with the appropriate resolution.
-    * Note that even if depth or stencil is *not* enabled, if it's
-    * present in the buffer, we pull it out and put it back later;
-    * otherwise, we can inadvertently destroy the contents of
-    * buffers we're not supposed to touch (e.g., if the user is
-    * clearing the depth buffer but not the stencil buffer, a
-    * quad of constant depth is drawn over the surface; the stencil
-    * buffer must be maintained).
+   /**
+    * The following code:
+    * 1. fetch quad of packed Z/S values from the framebuffer tile.
+    * 2. extract the separate the Z and S values from packed values
+    * 3. convert fragment Z values from float in [0,1] to 32/24/16-bit ints
+    *
+    * The instructions for doing this are interleaved for better performance.
     */
+   spe_comment(f, 0, "Fetch Z/stencil quad from tile");
+
    switch(zs_format) {
    case PIPE_FORMAT_S8Z24_UNORM: /* fall through */
    case PIPE_FORMAT_X8Z24_UNORM:
-      /* Pull out both Z and stencil */
-      setup_optional_register(f, &fbZ_reg);
-      setup_optional_register(f, &fbS_reg);
+      /* prepare mask to extract Z vals from ZS vals */
+      spe_load_uint(f, zmask_reg, 0x00ffffff);
 
-      /* four 24-bit Z values in the low-order bits */
-      spe_and_uint(f, fbZ_reg, fbZS_reg, 0x00ffffff);
-
-      /* Incoming fragZ_reg value is a float in 0.0...1.0; convert
-       * to a 24-bit unsigned integer
-       */
+      /* convert fragment Z from [0,1] to 32-bit ints */
       spe_cfltu(f, fragZ_reg, fragZ_reg, 32);
+
+      /* Load: fbZS_reg = memory[depth_tile_reg + offset_reg] */
+      spe_lqx(f, fbZS_reg, depth_tile_reg, quad_offset_reg);
+
+      /* right shift 32-bit fragment Z to 24 bits */
       spe_rotmi(f, fragZ_reg, fragZ_reg, -8);
 
-      /* four 8-bit stencil values in the high-order bits */
+      /* extract 24-bit Z values from ZS values by masking */
+      spe_and(f, fbZ_reg, fbZS_reg, zmask_reg);
+
+      /* extract 8-bit stencil values by shifting */
       spe_rotmi(f, fbS_reg, fbZS_reg, -24);
       break;
 
    case PIPE_FORMAT_Z24S8_UNORM: /* fall through */
    case PIPE_FORMAT_Z24X8_UNORM:
-      setup_optional_register(f, &fbZ_reg);
-      setup_optional_register(f, &fbS_reg);
+      /* convert fragment Z from [0,1] to 32-bit ints */
+      spe_cfltu(f, fragZ_reg, fragZ_reg, 32);
 
-      /* shift by 8 to get the upper 24-bit values */
-      spe_rotmi(f, fbS_reg, fbZS_reg, -8);
+      /* Load: fbZS_reg = memory[depth_tile_reg + offset_reg] */
+      spe_lqx(f, fbZS_reg, depth_tile_reg, quad_offset_reg);
 
-      /* Incoming fragZ_reg value is a float in 0.0...1.0; convert
-       * to a 24-bit unsigned integer
-       */
-      spe_cfltu(f, fragZ_reg, fragZ_reg, 32);
+      /* right shift 32-bit fragment Z to 24 bits */
       spe_rotmi(f, fragZ_reg, fragZ_reg, -8);
 
-      /* 8-bit stencil in the low-order bits - mask them out */
+      /* extract 24-bit Z values from ZS values by shifting */
+      spe_rotmi(f, fbZ_reg, fbZS_reg, -8);
+
+      /* extract 8-bit stencil values by masking */
       spe_and_uint(f, fbS_reg, fbZS_reg, 0x000000ff);
       break;
 
    case PIPE_FORMAT_Z32_UNORM:
-      setup_optional_register(f, &fbZ_reg);
-      /* Copy over 4 32-bit values */
-      spe_move(f, fbZ_reg, fbZS_reg);
+      /* Load: fbZ_reg = memory[depth_tile_reg + offset_reg] */
+      spe_lqx(f, fbZ_reg, depth_tile_reg, quad_offset_reg);
 
-      /* Incoming fragZ_reg value is a float in 0.0...1.0; convert
-       * to a 32-bit unsigned integer
-       */
+      /* convert fragment Z from [0,1] to 32-bit ints */
       spe_cfltu(f, fragZ_reg, fragZ_reg, 32);
+
       /* No stencil, so can't do anything there */
       break;
 
    case PIPE_FORMAT_Z16_UNORM:
-      /* XXX Not sure this is correct, but it was here before, so we're
-       * going with it for now
-       */
-      setup_optional_register(f, &fbZ_reg);
+      /* XXX This code for 16bpp Z is broken! */
+
+      /* Load: fbZS_reg = memory[depth_tile_reg + offset_reg] */
+      spe_lqx(f, fbZS_reg, depth_tile_reg, quad_offset_reg);
+
       /* Copy over 4 32-bit values */
       spe_move(f, fbZ_reg, fbZS_reg);
 
-      /* Incoming fragZ_reg value is a float in 0.0...1.0; convert
-       * to a 16-bit unsigned integer
-       */
+      /* convert Z from [0,1] to 16-bit ints */
       spe_cfltu(f, fragZ_reg, fragZ_reg, 32);
       spe_rotmi(f, fragZ_reg, fragZ_reg, -16);
       /* No stencil */
@@ -1979,9 +1974,10 @@ gen_depth_stencil(struct cell_context *cell,
    }
 
    /* Don't need these any more */
-   release_optional_register(f, fbZ_reg);
-   release_optional_register(f, fbS_reg);
    spe_release_register(f, fbZS_reg);
+   spe_release_register(f, fbZ_reg);
+   spe_release_register(f, fbS_reg);
+   spe_release_register(f, zmask_reg);
 }