i965: Fix register allocation of GLSL fp inputs.

Before, if the VP output something that is in the attributes coming into
the WM but which isn't used by the WM, then WM would end up reading subsequent
varyings from the wrong places.  This was visible with a GLSL demo
using gl_PointSize in the VS and a varying in the WM, as point size is in
the VUE but not used by the WM.  There is now a regression test in piglit,
glsl-unused-varying.

1 files changed, 21 insertions, 10 deletions

diff --git a/src/mesa/drivers/dri/i965/brw_wm_glsl.c b/src/mesa/drivers/dri/i965/brw_wm_glsl.c
index 23caf59435..4936703799 100644
--- a/src/mesa/drivers/dri/i965/brw_wm_glsl.c
+++ b/src/mesa/drivers/dri/i965/brw_wm_glsl.c
@@ -302,7 +302,7 @@ static void prealloc_reg(struct brw_wm_compile *c)
 {
     int i, j;
     struct brw_reg reg;
-    int nr_interp_regs = 0;
+    int urb_read_length = 0;
     GLuint inputs = FRAG_BIT_WPOS | c->fp_interp_emitted | c->fp_deriv_emitted;
     GLuint reg_index = 0;
 
@@ -366,18 +366,29 @@ static void prealloc_reg(struct brw_wm_compile *c)
     }
 
     /* fragment shader inputs */
-    for (i = 0; i < FRAG_ATTRIB_MAX; i++) {
-	if (inputs & (1<<i)) {
-	    nr_interp_regs++;
-	    reg = brw_vec8_grf(reg_index, 0);
-	    for (j = 0; j < 4; j++)
-		set_reg(c, PROGRAM_PAYLOAD, i, j, reg);
-	    reg_index += 2;
-	}
+    for (i = 0; i < VERT_RESULT_MAX; i++) {
+       int fp_input;
+
+       if (i >= VERT_RESULT_VAR0)
+	  fp_input = i - VERT_RESULT_VAR0 + FRAG_ATTRIB_VAR0;
+       else if (i <= VERT_RESULT_TEX7)
+	  fp_input = i;
+       else
+	  fp_input = -1;
+
+       if (fp_input >= 0 && inputs & (1 << fp_input)) {
+	  urb_read_length = reg_index;
+	  reg = brw_vec8_grf(reg_index, 0);
+	  for (j = 0; j < 4; j++)
+	     set_reg(c, PROGRAM_PAYLOAD, fp_input, j, reg);
+       }
+       if (c->key.vp_outputs_written & (1 << i)) {
+	  reg_index += 2;
+       }
     }
 
     c->prog_data.first_curbe_grf = c->key.nr_depth_regs * 2;
-    c->prog_data.urb_read_length = nr_interp_regs * 2;
+    c->prog_data.urb_read_length = urb_read_length;
     c->prog_data.curb_read_length = c->nr_creg;
     c->emit_mask_reg = brw_uw1_reg(BRW_GENERAL_REGISTER_FILE, reg_index, 0);
     reg_index++;