Mesa (master): i965/vec4: Use reads_accumulator_implicitly(), not MACH checks.

[Kenneth Graunke]

Module: Mesa
Branch: master
Commit: 6b10c37b9c3a73add73f444fe1aee73c9ec82c94
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=6b10c37b9c3a73add73f444fe1aee73c9ec82c94

Author: Kenneth Graunke <kenneth at whitecape.org>
Date:   Sat Apr 22 15:02:08 2017 -0700

i965/vec4: Use reads_accumulator_implicitly(), not MACH checks.

Curro pointed out that I should not just check for MACH, but use
the reads_accumulator_implicitly() helper, which would also prevent
the same bug with MAC and SADA2 (if we ever decide to use them).

Cc: mesa-stable at lists.freedesktop.org
Reviewed-by: Francisco Jerez <currojerez at riseup.net>

---

 src/intel/compiler/brw_vec4.cpp | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/intel/compiler/brw_vec4.cpp b/src/intel/compiler/brw_vec4.cpp
index 4bb774bf10..0909ddb586 100644
--- a/src/intel/compiler/brw_vec4.cpp
+++ b/src/intel/compiler/brw_vec4.cpp
@@ -1071,11 +1071,11 @@ vec4_instruction::can_reswizzle(const struct gen_device_info *devinfo,
    if (devinfo->gen == 6 && is_math() && swizzle != BRW_SWIZZLE_XYZW)
       return false;
 
-   /* Don't touch MACH - it uses the accumulator results from an earlier
-    * MUL - so we'd need to reswizzle both.  We don't do that, so just
-    * avoid it entirely.
+   /* We can't swizzle implicit accumulator access.  We'd have to
+    * reswizzle the producer of the accumulator value in addition
+    * to the consumer (i.e. both MUL and MACH).  Just skip this.
     */
-   if (opcode == BRW_OPCODE_MACH)
+   if (reads_accumulator_implicitly())
       return false;
 
    if (!can_do_writemask(devinfo) && dst_writemask != WRITEMASK_XYZW)