[Mesa-dev] [PATCH 04/13] i965: Mask out unused Align16 components in brw_untyped_atomic.

[Francisco Jerez]

This is currently not a problem because the vec4 visitor happens to
mask out unused components from the destination, but it might become
an issue when we start using atomics without writeback message.  In
any case it seems sensible to set it again here because the
consequences of setting the wrong writemask (random graphics memory
corruption) are difficult to debug and can easily go unnoticed.
---
 src/mesa/drivers/dri/i965/brw_eu_emit.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_eu_emit.c b/src/mesa/drivers/dri/i965/brw_eu_emit.c
index 2b1d6ff..0b655d4 100644
--- a/src/mesa/drivers/dri/i965/brw_eu_emit.c
+++ b/src/mesa/drivers/dri/i965/brw_eu_emit.c
@@ -2799,16 +2799,25 @@ brw_untyped_atomic(struct brw_compile *p,
                    bool response_expected)
 {
    const struct brw_context *brw = p->brw;
+   const bool align1 = (brw_inst_access_mode(brw, p->current) == BRW_ALIGN_1);
+   /* Mask out unused components -- This is especially important in Align16
+    * mode on generations that don't have native support for SIMD4x2 atomics,
+    * because unused but enabled components will cause the dataport to perform
+    * additional atomic operations on the addresses that happen to be in the
+    * uninitialized Y, Z and W coordinates of the payload.
+    */
+   const unsigned mask = (align1 ? WRITEMASK_XYZW : WRITEMASK_X);
    brw_inst *insn = brw_next_insn(p, BRW_OPCODE_SEND);
 
-   brw_set_dest(p, insn, retype(dest, BRW_REGISTER_TYPE_UD));
+   brw_set_dest(p, insn, retype(brw_writemask(dest, mask),
+                                BRW_REGISTER_TYPE_UD));
    brw_set_src0(p, insn, retype(payload, BRW_REGISTER_TYPE_UD));
    brw_set_src1(p, insn, brw_imm_d(0));
    brw_set_dp_untyped_atomic_message(
       p, insn, atomic_op, bind_table_index, msg_length,
       brw_surface_payload_size(p, response_expected,
                                brw->gen >= 8 || brw->is_haswell, true),
-      brw_inst_access_mode(brw, insn) == BRW_ALIGN_1);
+      align1);
 }
 
 static void
-- 
2.1.3