From: Kenneth Graunke <kenneth@whitecape.org>
Date: Fri, 21 Apr 2017 08:28:13 +0000 (-0700)
Subject: i965/vec4: Avoid reswizzling MACH instructions in opt_register_coalesce().
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=2faf227ec2e22c7a37e0a54783a3f0a0062ac852;p=mesa.git

i965/vec4: Avoid reswizzling MACH instructions in opt_register_coalesce().

opt_register_coalesce() was optimizing sequences such as:

   mul(8) acc0:D, attr18.xyyy:D, attr19.xyyy:D
   mach(8) vgrf5.xy:D, attr18.xyyy:D, attr19.xyyy:D
   mov(8) m4.zw:F, vgrf5.xxxy:F

into:

   mul(8) acc0:D, attr18.xyyy:D, attr19.xyyy:D
   mach(8) m4.zw:D, attr18.xxxy:D, attr19.xxxy:D

This doesn't work - if we're going to reswizzle MACH, we'd need to
reswizzle the MUL as well.  Here, the MUL fills the accumulator's .zw
components with attr18.yy * attr19.yy.  But the MACH instruction expects
.z to contain attr18.x * attr19.x.  Bogus results ensue.

No change in shader-db on Haswell.  Prevents regressions in Timothy's
patches to use enhanced layouts for varying packing (which rearrange
code just enough to trigger this pre-existing bug, but were fine
themselves).

Acked-by: Timothy Arceri <tarceri@itsqueeze.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
---

diff --git a/src/intel/compiler/brw_vec4.cpp b/src/intel/compiler/brw_vec4.cpp
index 0b92ba704e5..4bb774bf10e 100644
--- a/src/intel/compiler/brw_vec4.cpp
+++ b/src/intel/compiler/brw_vec4.cpp
@@ -1071,6 +1071,13 @@ 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.
+    */
+   if (opcode == BRW_OPCODE_MACH)
+      return false;
+
    if (!can_do_writemask(devinfo) && dst_writemask != WRITEMASK_XYZW)
       return false;