CELL: two-sided stencil fixes

With these changes, the tests/stencil_twoside test now works.

- Eliminate blending from the stencil_twoside test, as it produces an
  unneeded dependency on having blending working

- The spe_splat() function will now work if the register being splatted
  and the destination register are the same

- Separate fragment code generated for front-facing and back-facing
  fragments.  Often these are the same; if two-sided stenciling is on,
  they can be different.  This is easier and faster than generating
  code that does both tests and merges the results.

- Fixed a cut/paste bug where if the back Z-pass stencil operation
  were different from all the other operations, the back Z-fail
  results were incorrect.

10 files changed, 110 insertions, 204 deletions

diff --git a/src/gallium/drivers/cell/common.h b/src/gallium/drivers/cell/common.h
index 87488ea..a670ed3 100644
--- a/src/gallium/drivers/cell/common.h
+++ b/src/gallium/drivers/cell/common.h
@@ -130,6 +130,9 @@
 #define CELL_FENCE_EMITTED   1
 #define CELL_FENCE_SIGNALLED 2
 
+#define CELL_FACING_FRONT    0
+#define CELL_FACING_BACK     1
+
 struct cell_fence
 {
    /** There's a 16-byte status qword per SPU */
@@ -160,7 +163,8 @@ struct cell_command_fragment_ops
    struct pipe_depth_stencil_alpha_state dsa;
    struct pipe_blend_state blend;
    struct pipe_blend_color blend_color;
-   unsigned code[SPU_MAX_FRAGMENT_OPS_INSTS];
+   unsigned code_front[SPU_MAX_FRAGMENT_OPS_INSTS];
+   unsigned code_back[SPU_MAX_FRAGMENT_OPS_INSTS];
 };
 
 
diff --git a/src/gallium/drivers/cell/ppu/cell_gen_fragment.c b/src/gallium/drivers/cell/ppu/cell_gen_fragment.c
index d9c3ff3..6e425ea 100644
--- a/src/gallium/drivers/cell/ppu/cell_gen_fragment.c
+++ b/src/gallium/drivers/cell/ppu/cell_gen_fragment.c
@@ -1412,144 +1412,72 @@ gen_stencil_values(struct spe_function *f, unsigned int stencil_op,
  * and released by the corresponding spe_release_register_set() call.
  */
 static void
-gen_get_stencil_values(struct spe_function *f, const struct pipe_depth_stencil_alpha_state *dsa,
+gen_get_stencil_values(struct spe_function *f, const struct pipe_stencil_state *stencil,
+                       const unsigned int depth_enabled,
                        unsigned int fbS_reg, 
                        unsigned int *fail_reg, unsigned int *zfail_reg, 
-                       unsigned int *zpass_reg, unsigned int *back_fail_reg, 
-                       unsigned int *back_zfail_reg, unsigned int *back_zpass_reg)
+                       unsigned int *zpass_reg)
 {
-   unsigned zfail_op, back_zfail_op;
+   unsigned zfail_op;
 
    /* Stenciling had better be enabled here */
-   ASSERT(dsa->stencil[0].enabled);
+   ASSERT(stencil->enabled);
 
    /* If the depth test is not enabled, it is treated as though it always
-    * passes.  In particular, that means that the "zfail_op" (and the backfacing
-    * counterpart, if active) are not considered - a failing stencil test will
-    * trigger the "fail_op", and a passing stencil test will trigger the
-    * "zpass_op".
+    * passes, which means that the zfail_op is not considered - a
+    * failing stencil test triggers the fail_op, and a passing one
+    * triggers the zpass_op
     *
-    * By overriding the operations in this case to be PIPE_STENCIL_OP_KEEP,
-    * we keep them from being calculated.
+    * As an optimization, override calculation of the zfail_op values
+    * if they aren't going to be used.  By setting the value of
+    * the operation to PIPE_STENCIL_OP_KEEP, its value will be assumed
+    * to match the incoming stencil values, and no calculation will
+    * be done.
     */
-   if (dsa->depth.enabled) {
-      zfail_op = dsa->stencil[0].zfail_op;
-      back_zfail_op = dsa->stencil[1].zfail_op;
+   if (depth_enabled) {
+      zfail_op = stencil->zfail_op;
    }
    else {
       zfail_op = PIPE_STENCIL_OP_KEEP;
-      back_zfail_op = PIPE_STENCIL_OP_KEEP;
    }
 
    /* One-sided or front-facing stencil */
-   if (dsa->stencil[0].fail_op == PIPE_STENCIL_OP_KEEP) {
+   if (stencil->fail_op == PIPE_STENCIL_OP_KEEP) {
       *fail_reg = fbS_reg;
    }
    else {
       *fail_reg = spe_allocate_available_register(f);
-      gen_stencil_values(f, dsa->stencil[0].fail_op, dsa->stencil[0].ref_value, 
+      gen_stencil_values(f, stencil->fail_op, stencil->ref_value, 
          0xff, fbS_reg, *fail_reg);
    }
 
+   /* Check the possibly overridden value, not the structure value */
    if (zfail_op == PIPE_STENCIL_OP_KEEP) {
       *zfail_reg = fbS_reg;
    }
-   else if (zfail_op == dsa->stencil[0].fail_op) {
+   else if (zfail_op == stencil->fail_op) {
       *zfail_reg = *fail_reg;
    }
    else {
       *zfail_reg = spe_allocate_available_register(f);
-      gen_stencil_values(f, dsa->stencil[0].zfail_op, dsa->stencil[0].ref_value, 
+      gen_stencil_values(f, stencil->zfail_op, stencil->ref_value, 
          0xff, fbS_reg, *zfail_reg);
    }
 
-   if (dsa->stencil[0].zpass_op == PIPE_STENCIL_OP_KEEP) {
+   if (stencil->zpass_op == PIPE_STENCIL_OP_KEEP) {
       *zpass_reg = fbS_reg;
    }
-   else if (dsa->stencil[0].zpass_op == dsa->stencil[0].fail_op) {
+   else if (stencil->zpass_op == stencil->fail_op) {
       *zpass_reg = *fail_reg;
    }
-   else if (dsa->stencil[0].zpass_op == zfail_op) {
+   else if (stencil->zpass_op == zfail_op) {
       *zpass_reg = *zfail_reg;
    }
    else {
       *zpass_reg = spe_allocate_available_register(f);
-      gen_stencil_values(f, dsa->stencil[0].zpass_op, dsa->stencil[0].ref_value, 
+      gen_stencil_values(f, stencil->zpass_op, stencil->ref_value, 
          0xff, fbS_reg, *zpass_reg);
    }
-
-   /* If two-sided stencil is enabled, we have more work to do. */
-   if (!dsa->stencil[1].enabled) {
-      /* This just flags that the registers need not be deallocated later */
-      *back_fail_reg = fbS_reg;
-      *back_zfail_reg = fbS_reg;
-      *back_zpass_reg = fbS_reg;
-   }
-   else {
-      /* Same calculations as above, but for the back stencil */
-      if (dsa->stencil[1].fail_op == PIPE_STENCIL_OP_KEEP) {
-         *back_fail_reg = fbS_reg;
-      }
-      else if (dsa->stencil[1].fail_op == dsa->stencil[0].fail_op) {
-         *back_fail_reg = *fail_reg;
-      }
-      else if (dsa->stencil[1].fail_op == zfail_op) {
-         *back_fail_reg = *zfail_reg;
-      }
-      else if (dsa->stencil[1].fail_op == dsa->stencil[0].zpass_op) {
-         *back_fail_reg = *zpass_reg;
-      }
-      else {
-         *back_fail_reg = spe_allocate_available_register(f);
-         gen_stencil_values(f, dsa->stencil[1].fail_op, dsa->stencil[1].ref_value, 
-            0xff, fbS_reg, *back_fail_reg);
-      }
-
-      if (back_zfail_op == PIPE_STENCIL_OP_KEEP) {
-         *back_zfail_reg = fbS_reg;
-      }
-      else if (back_zfail_op == dsa->stencil[0].fail_op) {
-         *back_zfail_reg = *fail_reg;
-      }
-      else if (back_zfail_op == zfail_op) {
-         *back_zfail_reg = *zfail_reg;
-      }
-      else if (back_zfail_op == dsa->stencil[0].zpass_op) {
-         *back_zfail_reg = *zpass_reg;
-      }
-      else if (back_zfail_op == dsa->stencil[1].fail_op) {
-         *back_zfail_reg = *back_fail_reg;
-      }
-      else {
-         *back_zfail_reg = spe_allocate_available_register(f);
-         gen_stencil_values(f, dsa->stencil[1].zfail_op, dsa->stencil[1].ref_value, 
-            0xff, fbS_reg, *back_zfail_reg);
-      }
-
-      if (dsa->stencil[1].zpass_op == PIPE_STENCIL_OP_KEEP) {
-         *back_zpass_reg = fbS_reg;
-      }
-      else if (dsa->stencil[1].zpass_op == dsa->stencil[0].fail_op) {
-         *back_zpass_reg = *fail_reg;
-      }
-      else if (dsa->stencil[1].zpass_op == zfail_op) {
-         *back_zpass_reg = *zfail_reg;
-      }
-      else if (dsa->stencil[1].zpass_op == dsa->stencil[0].zpass_op) {
-         *back_zpass_reg = *zpass_reg;
-      }
-      else if (dsa->stencil[1].zpass_op == dsa->stencil[1].fail_op) {
-         *back_zpass_reg = *back_fail_reg;
-      }
-      else if (dsa->stencil[1].zpass_op == back_zfail_op) {
-         *back_zpass_reg = *back_zfail_reg;
-      }
-      else {
-         *back_zfail_reg = spe_allocate_available_register(f);
-         gen_stencil_values(f, dsa->stencil[1].zpass_op, dsa->stencil[1].ref_value, 
-            0xff, fbS_reg, *back_zpass_reg);
-      }
-   } /* End of calculations for back-facing stencil */
 }
 
 /* Note that fbZ_reg may *not* be set on entry, if in fact
@@ -1559,7 +1487,7 @@ gen_get_stencil_values(struct spe_function *f, const struct pipe_depth_stencil_a
 static boolean
 gen_stencil_depth_test(struct spe_function *f, 
                        const struct pipe_depth_stencil_alpha_state *dsa, 
-                       const int const facing_reg,
+                       const uint facing,
                        const int mask_reg, const int fragZ_reg, 
                        const int fbZ_reg, const int fbS_reg)
 {
@@ -1571,6 +1499,8 @@ gen_stencil_depth_test(struct spe_function *f,
    boolean need_to_calculate_stencil_values;
    boolean need_to_writemask_stencil_values;
 
+   struct pipe_stencil_state *stencil;
+
    /* Registers.  We may or may not actually allocate these, depending
     * on whether the state values indicate that we need them.
     */
@@ -1598,6 +1528,20 @@ gen_stencil_depth_test(struct spe_function *f,
    spe_comment(f, 0, "Allocating stencil register set");
    spe_allocate_register_set(f);
 
+   /* The facing we're given is the fragment facing; it doesn't
+    * exactly match the stencil facing.  If stencil is enabled,
+    * but two-sided stencil is *not* enabled, we use the same
+    * stencil settings for both front- and back-facing fragments.
+    * We only use the "back-facing" stencil for backfacing fragments
+    * if two-sided stenciling is enabled.
+    */
+   if (facing == CELL_FACING_BACK && dsa->stencil[1].enabled) {
+      stencil = &dsa->stencil[1];
+   }
+   else {
+      stencil = &dsa->stencil[0];
+   }
+
    /* Calculate the writemask.  If the writemask is trivial (either
     * all 0s, meaning that we don't need to calculate any stencil values
     * because they're not going to change the stencil anyway, or all 1s,
@@ -1608,24 +1552,20 @@ gen_stencil_depth_test(struct spe_function *f,
     * Note that if the backface stencil is *not* enabled, the backface
     * stencil will have the same values as the frontface stencil.
     */
-   if (dsa->stencil[0].fail_op == PIPE_STENCIL_OP_KEEP &&
-       dsa->stencil[0].zfail_op == PIPE_STENCIL_OP_KEEP &&
-       dsa->stencil[0].zpass_op == PIPE_STENCIL_OP_KEEP &&
-       dsa->stencil[1].fail_op == PIPE_STENCIL_OP_KEEP &&
-       dsa->stencil[1].zfail_op == PIPE_STENCIL_OP_KEEP &&
-       dsa->stencil[1].zpass_op == PIPE_STENCIL_OP_KEEP) {
-       /* No changes to any stencil values */
+   if (stencil->fail_op == PIPE_STENCIL_OP_KEEP &&
+       stencil->zfail_op == PIPE_STENCIL_OP_KEEP &&
+       stencil->zpass_op == PIPE_STENCIL_OP_KEEP) {
        need_to_calculate_stencil_values = false;
        need_to_writemask_stencil_values = false;
     }
-    else if (dsa->stencil[0].write_mask == 0x0 && dsa->stencil[1].write_mask == 0x0) {
+    else if (stencil->write_mask == 0x0) {
       /* All changes are writemasked out, so no need to calculate
        * what those changes might be, and no need to write anything back.
        */
       need_to_calculate_stencil_values = false;
       need_to_writemask_stencil_values = false;
    }
-   else if (dsa->stencil[0].write_mask == 0xff && dsa->stencil[1].write_mask == 0xff) {
+   else if (stencil->write_mask == 0xff) {
       /* Still trivial, but a little less so.  We need to write the stencil
        * values, but we don't need to mask them.
        */
@@ -1645,14 +1585,7 @@ gen_stencil_depth_test(struct spe_function *f,
        */
       spe_comment(f, 0, "Computing stencil writemask");
       stencil_writemask_reg = spe_allocate_available_register(f);
-      spe_load_uint(f, stencil_writemask_reg, dsa->stencil[0].write_mask);
-      if (dsa->stencil[1].enabled && dsa->stencil[0].write_mask != dsa->stencil[1].write_mask) {
-         unsigned int back_write_mask_reg = spe_allocate_available_register(f);
-         spe_comment(f, 0, "Resolving two-sided stencil writemask");
-         spe_load_uint(f, back_write_mask_reg, dsa->stencil[1].write_mask);
-         spe_selb(f, stencil_writemask_reg, stencil_writemask_reg, back_write_mask_reg, facing_reg);
-         spe_release_register(f, back_write_mask_reg);
-      }
+      spe_load_uint(f, stencil_writemask_reg, dsa->stencil[facing].write_mask);
    }
 
    /* At least one-sided stenciling must be on.  Generate code that
@@ -1666,19 +1599,7 @@ gen_stencil_depth_test(struct spe_function *f,
     */
    spe_comment(f, 0, "Running basic stencil test");
    stencil_pass_reg = spe_allocate_available_register(f);
-   gen_stencil_test(f, &dsa->stencil[0], 0xff, mask_reg, fbS_reg, stencil_pass_reg);
-
-   /* If two-sided stenciling is on, generate code to run the stencil
-    * test on the backfacing stencil as well, and combine the two results
-    * into the one correct result based on facing.
-    */
-   if (dsa->stencil[1].enabled) {
-      unsigned int temp_reg = spe_allocate_available_register(f);
-      spe_comment(f, 0, "Running backface stencil test");
-      gen_stencil_test(f, &dsa->stencil[1], 0xff, mask_reg, fbS_reg, temp_reg);
-      spe_selb(f, stencil_pass_reg, stencil_pass_reg, temp_reg, facing_reg);
-      spe_release_register(f, temp_reg);
-   }
+   gen_stencil_test(f, stencil, 0xff, mask_reg, fbS_reg, stencil_pass_reg);
 
    /* Generate code that, given the mask of valid fragments and the
     * mask of valid fragments that passed the stencil test, computes
@@ -1698,9 +1619,6 @@ gen_stencil_depth_test(struct spe_function *f,
 
    /* We may not need to calculate stencil values, if the writemask is off */
    if (need_to_calculate_stencil_values) {
-      unsigned int back_stencil_fail_values, back_stencil_pass_depth_fail_values, back_stencil_pass_depth_pass_values;
-      unsigned int front_stencil_fail_values, front_stencil_pass_depth_fail_values, front_stencil_pass_depth_pass_values;
-
       /* Generate code that calculates exactly which stencil values we need,
        * without calculating the same value twice (say, if two different
        * stencil ops have the same value).  This code will work for one-sided
@@ -1715,51 +1633,11 @@ gen_stencil_depth_test(struct spe_function *f,
        * This function will allocate a variant number of registers that
        * will be released as part of the register set.
        */
-      spe_comment(f, 0, "Computing stencil values");
-      gen_get_stencil_values(f, dsa, fbS_reg, 
-         &front_stencil_fail_values, &front_stencil_pass_depth_fail_values, 
-         &front_stencil_pass_depth_pass_values, &back_stencil_fail_values, 
-         &back_stencil_pass_depth_fail_values, &back_stencil_pass_depth_pass_values);
-
-      /* Tricky, tricky, tricky - the things we do to create optimal
-       * code...
-       *
-       * The various stencil values registers may overlap with each other
-       * and with fbS_reg arbitrarily (as any particular operation is
-       * only calculated once and stored in one register, no matter
-       * how many times it is used).  So we can't change the values 
-       * within those registers directly - if we change a value in a
-       * register that's being referenced by two different calculations,
-       * we've just unwittingly changed the second value as well...
-       *
-       * Avoid this by allocating new registers to hold the results
-       * (there may be 2, if the depth test is off, or 3, if it is on).
-       * These will be released as part of the register set.
-       */
-      if (!dsa->stencil[1].enabled) {
-         /* The easy case: if two-sided stenciling is *not* enabled, we
-          * just use the front-sided values.
-          */
-         stencil_fail_values = front_stencil_fail_values;
-         stencil_pass_depth_fail_values = front_stencil_pass_depth_fail_values;
-         stencil_pass_depth_pass_values = front_stencil_pass_depth_pass_values;
-      }
-      else { /* two-sided stencil enabled */
-         spe_comment(f, 0, "Resolving backface stencil values");
-         /* Allocate new registers for the needed merged values */
-         stencil_fail_values = spe_allocate_available_register(f);
-         spe_selb(f, stencil_fail_values, front_stencil_fail_values, back_stencil_fail_values, facing_reg);
-         if (dsa->depth.enabled) {
-            stencil_pass_depth_fail_values = spe_allocate_available_register(f);
-            spe_selb(f, stencil_pass_depth_fail_values, front_stencil_pass_depth_fail_values, back_stencil_pass_depth_fail_values, facing_reg);
-         }
-         else {
-            stencil_pass_depth_fail_values = fbS_reg;
-         }
-         stencil_pass_depth_pass_values = spe_allocate_available_register(f);
-         spe_selb(f, stencil_pass_depth_pass_values, front_stencil_pass_depth_pass_values, back_stencil_pass_depth_pass_values, facing_reg);
-      }
-   }
+      spe_comment(f, 0, facing == CELL_FACING_FRONT ? "Computing front-facing stencil values" : "Computing back-facing stencil values");
+      gen_get_stencil_values(f, stencil, dsa->depth.enabled, fbS_reg, 
+         &stencil_fail_values, &stencil_pass_depth_fail_values, 
+         &stencil_pass_depth_pass_values);
+   }  
 
    /* We now have all the stencil values we need.  We also need 
     * the results of the depth test to figure out which
@@ -1896,10 +1774,12 @@ gen_stencil_depth_test(struct spe_function *f,
  * should be much faster.
  *
  * \param cell  the rendering context (in)
+ * \param facing whether the generated code is for front-facing or 
+ *              back-facing fragments
  * \param f     the generated function (out)
  */
 void
-cell_gen_fragment_function(struct cell_context *cell, struct spe_function *f)
+cell_gen_fragment_function(struct cell_context *cell, uint facing, struct spe_function *f)
 {
    const struct pipe_depth_stencil_alpha_state *dsa = cell->depth_stencil;
    const struct pipe_blend_state *blend = cell->blend;
@@ -1917,7 +1797,8 @@ cell_gen_fragment_function(struct cell_context *cell, struct spe_function *f)
    const int fragB_reg = 10;  /* vector float */
    const int fragA_reg = 11;  /* vector float */
    const int mask_reg = 12;   /* vector uint */
-   const int facing_reg = 13; /* uint */
+
+   ASSERT(facing == CELL_FACING_FRONT || facing == CELL_FACING_BACK);
 
    /* offset of quad from start of tile
     * XXX assuming 4-byte pixels for color AND Z/stencil!!!!
@@ -1945,7 +1826,6 @@ cell_gen_fragment_function(struct cell_context *cell, struct spe_function *f)
    spe_allocate_register(f, fragB_reg);
    spe_allocate_register(f, fragA_reg);
    spe_allocate_register(f, mask_reg);
-   spe_allocate_register(f, facing_reg);
 
    quad_offset_reg = spe_allocate_available_register(f);
    fbRGBA_reg = spe_allocate_available_register(f);
@@ -1969,6 +1849,7 @@ cell_gen_fragment_function(struct cell_context *cell, struct spe_function *f)
       spe_release_register(f, y2_reg);
    }
 
+   /* Generate the alpha test, if needed. */
    if (dsa->alpha.enabled) {
       gen_alpha_test(dsa, f, mask_reg, fragA_reg);
    }
@@ -2095,7 +1976,7 @@ cell_gen_fragment_function(struct cell_context *cell, struct spe_function *f)
           * gen_stencil_depth_test() function must ignore the
           * fbZ_reg register if depth is not enabled.
           */
-         write_depth_stencil = gen_stencil_depth_test(f, dsa, facing_reg, mask_reg, fragZ_reg, fbZ_reg, fbS_reg);
+         write_depth_stencil = gen_stencil_depth_test(f, dsa, facing, mask_reg, fragZ_reg, fbZ_reg, fbS_reg);
       }
       else if (dsa->depth.enabled) {
          int zmask_reg = spe_allocate_available_register(f);
diff --git a/src/gallium/drivers/cell/ppu/cell_gen_fragment.h b/src/gallium/drivers/cell/ppu/cell_gen_fragment.h
index b59de19..2fabfdf 100644
--- a/src/gallium/drivers/cell/ppu/cell_gen_fragment.h
+++ b/src/gallium/drivers/cell/ppu/cell_gen_fragment.h
@@ -31,7 +31,7 @@
 
 
 extern void
-cell_gen_fragment_function(struct cell_context *cell, struct spe_function *f);
+cell_gen_fragment_function(struct cell_context *cell, uint facing, struct spe_function *f);
 
 
 #endif /* CELL_GEN_FRAGMENT_H */
diff --git a/src/gallium/drivers/cell/ppu/cell_state_emit.c b/src/gallium/drivers/cell/ppu/cell_state_emit.c
index dd2d7f7..031b27f 100644
--- a/src/gallium/drivers/cell/ppu/cell_state_emit.c
+++ b/src/gallium/drivers/cell/ppu/cell_state_emit.c
@@ -75,23 +75,29 @@ lookup_fragment_ops(struct cell_context *cell)
     * If not found, create/save new fragment ops command.
     */
    if (!ops) {
-      struct spe_function spe_code;
+      struct spe_function spe_code_front, spe_code_back;
 
       if (0)
          debug_printf("**** Create New Fragment Ops\n");
 
       /* Prepare the buffer that will hold the generated code. */
-      spe_init_func(&spe_code, SPU_MAX_FRAGMENT_OPS_INSTS * SPE_INST_SIZE);
+      spe_init_func(&spe_code_front, SPU_MAX_FRAGMENT_OPS_INSTS * SPE_INST_SIZE);
+      spe_init_func(&spe_code_back, SPU_MAX_FRAGMENT_OPS_INSTS * SPE_INST_SIZE);
 
-      /* generate new code */
-      cell_gen_fragment_function(cell, &spe_code);
+      /* generate new code.  Always generate new code for both front-facing
+       * and back-facing fragments, even if it's the same code in both
+       * cases.
+       */
+      cell_gen_fragment_function(cell, CELL_FACING_FRONT, &spe_code_front);
+      cell_gen_fragment_function(cell, CELL_FACING_BACK, &spe_code_back);
 
       /* alloc new fragment ops command */
       ops = CALLOC_STRUCT(cell_command_fragment_ops);
 
       /* populate the new cell_command_fragment_ops object */
       ops->opcode = CELL_CMD_STATE_FRAGMENT_OPS;
-      memcpy(ops->code, spe_code.store, spe_code_size(&spe_code));
+      memcpy(ops->code_front, spe_code_front.store, spe_code_size(&spe_code_front));
+      memcpy(ops->code_back, spe_code_back.store, spe_code_size(&spe_code_back));
       ops->dsa = *cell->depth_stencil;
       ops->blend = *cell->blend;
 
@@ -99,7 +105,8 @@ lookup_fragment_ops(struct cell_context *cell)
       util_keymap_insert(cell->fragment_ops_cache, &key, ops, NULL);
 
       /* release rtasm buffer */
-      spe_release_func(&spe_code);
+      spe_release_func(&spe_code_front);
+      spe_release_func(&spe_code_back);
    }
    else {
       if (0)
diff --git a/src/gallium/drivers/cell/spu/spu_command.c b/src/gallium/drivers/cell/spu/spu_command.c
index d726622..d5faf4e 100644
--- a/src/gallium/drivers/cell/spu/spu_command.c
+++ b/src/gallium/drivers/cell/spu/spu_command.c
@@ -214,7 +214,8 @@ cmd_state_fragment_ops(const struct cell_command_fragment_ops *fops)
 
    D_PRINTF(CELL_DEBUG_CMD, "CMD_STATE_FRAGMENT_OPS\n");
    /* Copy SPU code from batch buffer to spu buffer */
-   memcpy(spu.fragment_ops_code, fops->code, SPU_MAX_FRAGMENT_OPS_INSTS * 4);
+   memcpy(spu.fragment_ops_code_front, fops->code_front, SPU_MAX_FRAGMENT_OPS_INSTS * 4);
+   memcpy(spu.fragment_ops_code_back, fops->code_back, SPU_MAX_FRAGMENT_OPS_INSTS * 4);
    /* Copy state info (for fallback case only) */
    memcpy(&spu.depth_stencil_alpha, &fops->dsa, sizeof(fops->dsa));
    memcpy(&spu.blend, &fops->blend, sizeof(fops->blend));
@@ -234,7 +235,8 @@ cmd_state_fragment_ops(const struct cell_command_fragment_ops *fops)
     * raw state records that the fallback code requires.
     */
    if ((spu.init.debug_flags & CELL_DEBUG_FRAGMENT_OP_FALLBACK) == 0) {
-      spu.fragment_ops = (spu_fragment_ops_func) spu.fragment_ops_code;
+      spu.fragment_ops[CELL_FACING_FRONT] = (spu_fragment_ops_func) spu.fragment_ops_code_front;
+      spu.fragment_ops[CELL_FACING_BACK] = (spu_fragment_ops_func) spu.fragment_ops_code_back;
    }
    else {
       /* otherwise, the default fallback code remains in place */
diff --git a/src/gallium/drivers/cell/spu/spu_main.c b/src/gallium/drivers/cell/spu/spu_main.c
index c8bb251..7033f60 100644
--- a/src/gallium/drivers/cell/spu/spu_main.c
+++ b/src/gallium/drivers/cell/spu/spu_main.c
@@ -63,7 +63,8 @@ one_time_init(void)
     * This will normally be overriden by a code-gen'd function
     * unless CELL_FORCE_FRAGMENT_OPS_FALLBACK is set.
     */
-   spu.fragment_ops = spu_fallback_fragment_ops;
+   spu.fragment_ops[CELL_FACING_FRONT] = spu_fallback_fragment_ops;
+   spu.fragment_ops[CELL_FACING_BACK] = spu_fallback_fragment_ops;
 }
 
 
@@ -90,7 +91,8 @@ main(main_param_t speid, main_param_t argp)
 
    ASSERT(sizeof(tile_t) == TILE_SIZE * TILE_SIZE * 4);
    ASSERT(sizeof(struct cell_command_render) % 8 == 0);
-   ASSERT(((unsigned long) &spu.fragment_ops_code) % 8 == 0);
+   ASSERT(((unsigned long) &spu.fragment_ops_code_front) % 8 == 0);
+   ASSERT(((unsigned long) &spu.fragment_ops_code_back) % 8 == 0);
    ASSERT(((unsigned long) &spu.fragment_program_code) % 8 == 0);
 
    one_time_init();
diff --git a/src/gallium/drivers/cell/spu/spu_main.h b/src/gallium/drivers/cell/spu/spu_main.h
index 692790c..24cf7d7 100644
--- a/src/gallium/drivers/cell/spu/spu_main.h
+++ b/src/gallium/drivers/cell/spu/spu_main.h
@@ -85,8 +85,7 @@ typedef void (*spu_fragment_ops_func)(uint x, uint y,
                                       vector float fragGreen,
                                       vector float fragBlue,
                                       vector float fragAlpha,
-                                      vector unsigned int mask,
-                                      uint facing);
+                                      vector unsigned int mask);
 
 /** Function for running fragment program */
 typedef vector unsigned int (*spu_fragment_program_func)(vector float *inputs,
@@ -170,9 +169,10 @@ struct spu_global
    ubyte ztile_status[CELL_MAX_HEIGHT/TILE_SIZE][CELL_MAX_WIDTH/TILE_SIZE] ALIGN16_ATTRIB;
 
    /** Current fragment ops machine code, at 8-byte boundary */
-   uint fragment_ops_code[SPU_MAX_FRAGMENT_OPS_INSTS] ALIGN8_ATTRIB;
-   /** Current fragment ops function */
-   spu_fragment_ops_func fragment_ops;
+   uint fragment_ops_code_front[SPU_MAX_FRAGMENT_OPS_INSTS] ALIGN8_ATTRIB;
+   uint fragment_ops_code_back[SPU_MAX_FRAGMENT_OPS_INSTS] ALIGN8_ATTRIB;
+   /** Current fragment ops functions, 0 = frontfacing, 1 = backfacing */
+   spu_fragment_ops_func fragment_ops[2];
 
    /** Current fragment program machine code, at 8-byte boundary */
    uint fragment_program_code[SPU_MAX_FRAGMENT_PROGRAM_INSTS] ALIGN8_ATTRIB;
diff --git a/src/gallium/drivers/cell/spu/spu_per_fragment_op.c b/src/gallium/drivers/cell/spu/spu_per_fragment_op.c
index f8ffc70..683664e 100644
--- a/src/gallium/drivers/cell/spu/spu_per_fragment_op.c
+++ b/src/gallium/drivers/cell/spu/spu_per_fragment_op.c
@@ -75,8 +75,7 @@ spu_fallback_fragment_ops(uint x, uint y,
                           vector float fragG,
                           vector float fragB,
                           vector float fragA,
-                          vector unsigned int mask,
-                          uint facing)
+                          vector unsigned int mask)
 {
    vector float frag_aos[4];
    unsigned int fbc0, fbc1, fbc2, fbc3 ; /* framebuffer/tile colors */
diff --git a/src/gallium/drivers/cell/spu/spu_per_fragment_op.h b/src/gallium/drivers/cell/spu/spu_per_fragment_op.h
index a61689c..f817abf 100644
--- a/src/gallium/drivers/cell/spu/spu_per_fragment_op.h
+++ b/src/gallium/drivers/cell/spu/spu_per_fragment_op.h
@@ -38,8 +38,7 @@ spu_fallback_fragment_ops(uint x, uint y,
                           vector float fragGreen,
                           vector float fragBlue,
                           vector float fragAlpha,
-                          vector unsigned int mask,
-                          uint facing);
+                          vector unsigned int mask);
 
 
 #endif /* SPU_PER_FRAGMENT_OP */
diff --git a/src/gallium/drivers/cell/spu/spu_tri.c b/src/gallium/drivers/cell/spu/spu_tri.c
index 5f90815..22e51a8 100644
--- a/src/gallium/drivers/cell/spu/spu_tri.c
+++ b/src/gallium/drivers/cell/spu/spu_tri.c
@@ -275,15 +275,20 @@ emit_quad( int x, int y, mask_t mask)
 
          /* Execute per-fragment/quad operations, including:
           * alpha test, z test, stencil test, blend and framebuffer writing.
+          * Note that there are two different fragment operations functions
+          * that can be called, one for front-facing fragments, and one
+          * for back-facing fragments.  (Often the two are the same;
+          * but in some cases, like two-sided stenciling, they can be
+          * very different.)  So choose the correct function depending
+          * on the calculated facing.
           */
-         spu.fragment_ops(ix, iy, &spu.ctile, &spu.ztile,
+         spu.fragment_ops[setup.facing](ix, iy, &spu.ctile, &spu.ztile,
                           fragZ,
                           outputs[0*4+0],
                           outputs[0*4+1],
                           outputs[0*4+2],
                           outputs[0*4+3],
-                          mask,
-                          setup.facing);
+                          mask);
       }
    }
 }
@@ -519,7 +524,14 @@ setup_sort_vertices(const struct vertex_header *v0,
 
    setup.oneOverArea = 1.0f / area;
 
-   /* The product of area * sign indicates front/back orientation (0/1) */
+   /* The product of area * sign indicates front/back orientation (0/1).
+    * Just in case someone gets the bright idea of switching the front
+    * and back constants without noticing that we're assuming their
+    * values in this operation, also assert that the values are
+    * what we think they are.
+    */
+   ASSERT(CELL_FACING_FRONT == 0);
+   ASSERT(CELL_FACING_BACK == 1);
    setup.facing = (area * sign > 0.0f)
       ^ (spu.rasterizer.front_winding == PIPE_WINDING_CW);