Normally, SEND messages read existing MRF values, which were previously
written by some other instruction. However, some meta-instructions
(like FS_OPCODE_UNIFORM_PULL_CONSTANT_LOAD) implicitly write MRFs before
reading them. In that case, the existing MRF values aren't actually
read.
Furthermore, from the point of view of the scheduler, such instructions
are a single atomic operation, since it isn't split into message setup
and SEND until code generation (fs_generator) time.
By ignoring any MRFs clobbered by implicit writes, we remove false
read-after-write and write-after-read dependencies.
NOTE: This is a candidate for the 9.1 branch.
Cc: Eric Anholt <e...@anholt.net>
Cc: Ian Romanick <i...@freedesktop.org>
Cc: Matt Turner <matts...@gmail.com>
Signed-off-by: Kenneth Graunke <kenn...@whitecape.org>
---
src/mesa/drivers/dri/i965/brw_fs_schedule_instructions.cpp | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)
diff --git a/src/mesa/drivers/dri/i965/brw_fs_schedule_instructions.cpp
b/src/mesa/drivers/dri/i965/brw_fs_schedule_instructions.cpp
index 3fbca6c..166b79f 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_schedule_instructions.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_schedule_instructions.cpp
@@ -495,7 +495,12 @@ instruction_scheduler::calculate_deps()
}
}
- for (int i = 0; i < inst->mlen; i++) {
+ /* Meta-instructions that use implied MRF writes internally write to
+ * the first few MRFs (as part of post-scheduling code generation).
+ * This means the existing values are not actually read, so we shouldn't
+ * consider them for RAW dependencies.
+ */
+ for (int i = v->implied_mrf_writes(inst); i < inst->mlen; i++) {
/* It looks like the MRF regs are released in the send
* instruction once it's sent, not when the result comes
* back.
@@ -600,7 +605,10 @@ instruction_scheduler::calculate_deps()
}
}
- for (int i = 0; i < inst->mlen; i++) {
+ /* Again, we don't actually read the existing value of any MRFs
+ * implicitly written by this instruction.
+ */
+ for (int i = v->implied_mrf_writes(inst); i < inst->mlen; i++) {
/* It looks like the MRF regs are released in the send
* instruction once it's sent, not when the result comes
* back.
--
1.8.1.3
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