Mesa (master): i965/fs: Disable CSE on instructions writing to HW_REG.

[Matt Turner]

Module: Mesa
Branch: master
Commit: 6ff8f0630833396fb7aff266657d4e1a04400719
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=6ff8f0630833396fb7aff266657d4e1a04400719

Author: Matt Turner <mattst88 at gmail.com>
Date:   Thu Sep 26 13:38:11 2013 -0700

i965/fs: Disable CSE on instructions writing to HW_REG.

CSE would otherwise combine the two mul(8) emitted by [iu]mulExtended:

	mul(8)  acc0 x y
	mach(8) null x y
	mov(8)  lsb  acc0
	...
	mul(8)  acc0 x y
	mach(8) msb  x y
Into:
	mul(8)  temp x y
	mov(8)  acc0 temp
	mach(8) null x y
	mov(8)  lsb  acc0
	...
	mov(8)  acc0 temp
	mach(8) msb  x y

But mul(8) into the accumulator produces more than 32-bits of precision,
which is required and lost if multiplying into a general register and
moving to the accumulator.

Reviewed-by: Eric Anholt <eric at anholt.net>

---

 src/mesa/drivers/dri/i965/brw_fs_cse.cpp |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_fs_cse.cpp b/src/mesa/drivers/dri/i965/brw_fs_cse.cpp
index ccd4e5e..61b3aeb 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_cse.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_cse.cpp
@@ -98,7 +98,8 @@ fs_visitor::opt_cse_local(bblock_t *block, exec_list *aeb)
       if (is_expression(inst) &&
           !inst->predicate &&
           !inst->is_partial_write() &&
-          !inst->conditional_mod)
+          !inst->conditional_mod &&
+          inst->dst.file != HW_REG)
       {
 	 bool found = false;