i965: Fix RNDZ and RNDE on Sandybridge and Ivybridge.

On gen4/5, the RNDZ and RNDE instructions return floor(x), but set special
"round increment bits" in the flag register; a predicated ADD (+1) fixes
the result.

The documentation still lists '.r' as existing, and says that the
predicated add is necessary, but it apparently lies.  According to the
simulator, BRW_CONDITIONAL_R (7) is not a valid conditional modifier
and the RNDZ and RNDE instructions simply produce the correct value.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Anholt <eric@anholt.net>

diff --git a/src/mesa/drivers/dri/i965/brw_eu_emit.c b/src/mesa/drivers/dri/i965/brw_eu_emit.c
index 19346b5917f2ad9f2cb2b634a54fe3bb0eeb3828..007f58c341c670bc9e37c71f59c5095f74401619 100644 (file)
--- a/src/mesa/drivers/dri/i965/brw_eu_emit.c
+++ b/src/mesa/drivers/dri/i965/brw_eu_emit.c
@@ -784,6 +784,8 @@ struct brw_instruction *brw_##OP(struct brw_compile *p,     \
  * stores a rounded value (possibly the wrong way) in the dest register, but
  * also sets a per-channel "increment bit" in the flag register.  A predicated
  * add of 1.0 fixes dest to contain the desired result.
+ *
+ * Sandybridge and later appear to round correctly without an ADD.
  */
 #define ROUND(OP)                                                            \
 void brw_##OP(struct brw_compile *p,                                         \
@@ -794,10 +796,13 @@ void brw_##OP(struct brw_compile *p,                                            \
    rnd = next_insn(p, BRW_OPCODE_##OP);                                              \
    brw_set_dest(p, rnd, dest);                                               \
    brw_set_src0(p, rnd, src);                                                \
-   rnd->header.destreg__conditionalmod = 0x7; /* turn on round-increments */  \
                                                                              \
-   add = brw_ADD(p, dest, dest, brw_imm_f(1.0f));                            \
-   add->header.predicate_control = BRW_PREDICATE_NORMAL;                     \
+   if (p->brw->intel.gen < 6) {                                                      \
+      /* turn on round-increments */                                         \
+      rnd->header.destreg__conditionalmod = BRW_CONDITIONAL_R;               \
+      add = brw_ADD(p, dest, dest, brw_imm_f(1.0f));                         \
+      add->header.predicate_control = BRW_PREDICATE_NORMAL;                  \
+   }                                                                         \
 }