Commit dc7f449d1ac53a66e6efb56ccf2a5953418a26ca introduced a new method
for avoiding MOVs: try to rewrite the destination of the instruction
that produced the RHS so it writes into the LHS.
Unfortunately, this is not safe for swizzled texturing operations, as
they return a set of four contiguous registers. Consider the following:
(assign (x)
(var_ref vec_ctor_x)
(swiz x (tex vec4 (var_ref m_sampY) (var_ref m_cordY) 0 1 ())))
In this case, the source and destination registers are equal, since
reg_offset is 0 for both. Yet, this is only a partial move: the texture
operation generates four registers, and the LHS only covers one.
Fixes color distortion in XBMC when using GLSL shaders.
NOTE: This is a candidate for the 8.0 branch (with the previous commit).
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=44333
Signed-off-by: Kenneth Graunke <kenn...@whitecape.org>
---
src/mesa/drivers/dri/i965/brw_fs_visitor.cpp | 6 ++++++
1 files changed, 6 insertions(+), 0 deletions(-)
diff --git a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
index e670ba7..bf1da9d 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
@@ -605,6 +605,12 @@ fs_visitor::try_rewrite_rhs_to_dst(ir_assignment *ir,
!src.equals(&last_rhs_inst->dst))
return false;
+ /* If last_rhs_inst wrote a different number of components than our LHS,
+ * we can't safely rewrite it.
+ */
+ if (ir->lhs->type->vector_elements != last_rhs_inst->regs_written())
+ return false;
+
/* Success! Rewrite the instruction. */
last_rhs_inst->dst = dst;
--
1.7.9
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