We already don't convert constants out of SSA, and in our backend we'd
like to have only one way of saying something is still in SSA.
The one tricky part about this is that we may now leave some undef
instructions around if they aren't part of a phi-web, so we have to be
more careful about deleting them.
v2: rename and flip meaning of flag (Jason)
Reviewed-by: Jason Ekstrand <jason.ekstrand@intel.com>
This commit switches us from the current setup of using hash sets for
use/def sets to using linked lists. Doing so should save us quite a bit of
memory because we aren't carrying around 3 hash sets per register and 2 per
SSA value. It should also save us CPU time because adding/removing things
from use/def sets is 4 pointer manipulations instead of a hash lookup.
Running shader-db 50 times with USE_NIR=0, NIR, and NIR + use/def lists:
GLSL IR Only: 586.4 +/- 1.653833
NIR with hash sets: 675.4 +/- 2.502108
NIR + use/def lists: 641.2 +/- 1.557043
I also ran a memory usage experiment with Ken's patch to delete GLSL IR and
keep NIR. This patch cuts an aditional 42.9 MiB of ralloc'd memory over
and above what we gained by deleting the GLSL IR on the same dota trace.
On the code complexity side of things, some things are now much easier and
others are a bit harder. One of the operations we perform constantly in
optimization passes is to replace one source with another. Due to the fact
that an instruction can use the same SSA value multiple times, we had to
iterate through the sources of the instruction and determine if the use we
were replacing was the only one before removing it from the set of uses.
With this patch, uses are per-source not per-instruction so we can just
remove it safely. On the other hand, trying to iterate over all of the
instructions that use a given value is more difficult. Fortunately, the
two places we do that are the ffma peephole where it doesn't matter and GCM
where we already gracefully handle duplicates visits to an instruction.
Another aspect here is that using linked lists in this way can be tricky to
get right. With sets, things were quite forgiving and the worst that
happened if you didn't properly remove a use was that it would get caught
in the validator. With linked lists, it can lead to linked list corruption
which can be harder to track. However, we do just as much validation of
the linked lists as we did of the sets so the validator should still catch
these problems. While working on this series, the vast majority of the
bugs I had to fix were caught by assertions. I don't think the lists are
going to be that much worse than the sets.
Reviewed-by: Connor Abbott <cwabbott0@gmail.com>
The out-of-SSA pass was one of the first passes written when getting SSA
up-and-going (for obvious reasons). As such, it came before a lot of the
nifty SSA-based helpers were introduced. This commit modernizes it so that
we're no longer doing nearly as much manual banging on use/def sets.
Reviewed-by: Connor Abbott <cwabbott0@gmail.com>
v2:
- Single statement, by using memset return value as suggested by Ian
Romanick.
- No internal declaration, as suggested by Jason Ekstrand.
- Move macros to a header.
Reviewed-by: Jason Ekstrand <jason.ekstrand@intel.com>
This is to enable the code to build with -Werror=vla in the short term,
and enable the code to build with MSVC2013 soon after.
Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
This adds a parent_instr field similar to the one for ssa_def. The
difference here is that the parent_instr field on a nir_register can be
NULL if the register does not have a unique definition or if that
definition does not dominate all its uses. We set this field in the
out-of-SSA pass so that backends can get SSA-like information even after
they have gone out of SSA.
Reviewed-by: Connor Abbott <cwabbott0@gmail.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Right now, the nir_instr_prev function function blindly looks up the
previous element in the exec list and casts it to an instruction even if
it's the tail sentinel. The next commit will change this to return null if
it's the first instruction. Making this change first avoids getting a
segfault between commits. The only reason we never noticed is that, thanks
to the way things are laid out in nir_block, the casted instruction's type
was never parallal_copy.
Reviewed-by: Connor Abbott <cwabbott0@gmail.com>
This avoids the overhead of copying structures and better matches the newly
added nir_alu_src_copy and nir_alu_dest_copy.
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Connor Abbott <cwabbott0@gmail.com>
Almost all instructions we nir_ssa_def_init() for are nir_dests, and you
have to keep from forgetting to set is_ssa when you do. Just provide the
simpler helper, instead.
Reviewed-by: Jason Ekstrand <jason.ekstrand@intel.com>
Designated initializers with anonymous unions don't work in MSVC or
GCC < 4.6. With a couple of constructor methods, we don't need them any
more and the code is actually cleaner.
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=88467
Reviewed-by: Connor Abbot <cwabbott0@gmail.com>
Previously, the set API required the user to do all of the hashing of keys
as it passed them in. Since the hashing function is intrinsically tied to
the comparison function, it makes sense for the hash set to know about
it. Also, it makes for a somewhat clumsy API as the user is constantly
calling hashing functions many of which have long names. This is
especially bad when the standard call looks something like
_mesa_set_add(ht, _mesa_pointer_hash(key), key);
In the above case, there is no reason why the hash set shouldn't do the
hashing for you. We leave the option for you to do your own hashing if
it's more efficient, but it's no longer needed. Also, if you do do your
own hashing, the hash set will assert that your hash matches what it
expects out of the hashing function. This should make it harder to mess up
your hashing.
This is analygous to 94303a0750 where we did this for hash_table
Signed-off-by: Jason Ekstrand <jason.ekstrand@intel.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
parallel_copy_copy was a silly name. Also, things were getting long and
annoying, so I added a foreach macro. For historical reasons, several of
the original iterations over parallel copy entries in from_ssa used the
_safe variants of the loop. However, all of these no longer ever remove an
entry so it's ok to make them all use the normal iterator.
Reviewed-by: Connor Abbott <cwabbott0@gmail.com>
Previously, we were doing a lazy creation of the parallel copy
instructions. This is confusing, hard to get right, and involves some
extra state tracking of the copies. This commit adds an extra walk over
the basic blocks to add the block-end parallel copies up front. This
should be much less confusing and, consequently, easier to get right. This
commit also adds more comments about parallel copies to help explain what
all is going on.
As a consequence of these changes, we can now remove the at_end parameter
from nir_parallel_copy_instr.
Reviewed-by: Connor Abbott <cwabbott0@gmail.com>
As it was, we weren't ever using load_const in a non-SSA way. This allows
us to substantially simplify the load_const instruction. If we ever need a
non-SSA constant load, we can do a load_const and an imov.
Reviewed-by: Connor Abbott <cwabbott0@gmail.com>
nir_metadata_dirty was a terrible name because the parameter it takes is
the metadata to be preserved. This is really confusing because it looks
like it's doing the opposite of what it is actually doing. Now it's named
sensibly.
Reviewed-by: Connor Abbott <cwabbott0@gmail.com>
Instead, we give SSA definitions a temporary index of 0xFFFFFFFF if the
instruction does not have a block and a proper index when it actually gets
added to the list.
Reviewed-by: Connor Abbott <cwabbott0@gmail.com>
Backends want to be able to do special things with constant values such as
put them into immediates or make decisions based on whether or not a value
is constant. Before, constants always got lowered to a load_const into a
register and then a register use. Now we leave constants as SSA values so
backends can special-case them if they want. Since handling constant SSA
values is trivial, this shouldn't be a problem for backends.
Reviewed-by: Connor Abbott <cwabbott0@gmail.com>
This commit rewrites the out-of-SSA pass to not be nearly as naieve. It's
based on "Revisiting Out-of-SSA Translation for Correctness, Code Quality,
and Efficiency" by Boissinot et. al. It should be fairly close to
state-of-the art.
Reviewed-by: Connor Abbott <cwabbott0@gmail.com>
Since we don't actually have an "if" instruction, this is a very common
pattern when iterating over instructions. This adds a helper function for
it to make things a little less painful.
Reviewed-by: Connor Abbott <cwabbott0@gmail.com>
This pass is kind of stupidly implemented but it should be enough to get us
up and going. We probably want something better that doesn't generate all
of the redundant moves eventually. However, the i965 backend should be
able to handle the movs, so I'm not too worried about it in the short term.
