[Mesa-dev] [PATCH v2 4/7] nir: add an instruction set API
Jason Ekstrand
jason at jlekstrand.net
Thu Oct 1 08:47:39 PDT 2015
On Thu, Oct 1, 2015 at 8:14 AM, Connor Abbott <cwabbott0 at gmail.com> wrote:
> On Wed, Sep 30, 2015 at 12:35 PM, Jason Ekstrand <jason at jlekstrand.net> wrote:
>> On Wed, Sep 30, 2015 at 8:11 AM, Connor Abbott <cwabbott0 at gmail.com> wrote:
>>> This will replace direct usage of nir_instrs_equal() in the CSE pass,
>>> which reduces an O(n^2) algorithm with an effectively O(n) one. It'll
>>> also be useful for implementing GVN on top of GCM.
>>>
>>> v2:
>>> - Add texture support.
>>> - Add more comments.
>>> - Rename instr_can_hash() to instr_can_rewrite() since it's really more
>>> about whether its uses can be rewritten, and it's implicitly used by
>>> nir_instrs_equal() as well.
>>> - Rename nir_instr_set_add() to nir_instr_set_add_or_rewrite() (Jason).
>>> - Make the HASH() macro less magical (Topi).
>>> - Rewrite the commit message.
>>>
>>> Signed-off-by: Connor Abbott <cwabbott0 at gmail.com>
>>> ---
>>> src/glsl/nir/nir_instr_set.c | 311 +++++++++++++++++++++++++++++++++++++++++++
>>> src/glsl/nir/nir_instr_set.h | 35 +++++
>>> 2 files changed, 346 insertions(+)
>>>
>>> diff --git a/src/glsl/nir/nir_instr_set.c b/src/glsl/nir/nir_instr_set.c
>>> index 72ab048..a6f2226 100644
>>> --- a/src/glsl/nir/nir_instr_set.c
>>> +++ b/src/glsl/nir/nir_instr_set.c
>>> @@ -23,6 +23,178 @@
>>>
>>> #include "nir_instr_set.h"
>>>
>>> +#define HASH(hash, data) _mesa_fnv32_1a_accumulate((hash), (data))
>>> +
>>> +static uint32_t
>>> +hash_src(uint32_t hash, const nir_src *src)
>>> +{
>>> + assert(src->is_ssa);
>>> + hash = HASH(hash, src->ssa);
>>> + return hash;
>>> +}
>>> +
>>> +static uint32_t
>>> +hash_alu_src(uint32_t hash, const nir_alu_src *src, unsigned num_components)
>>> +{
>>> + hash = HASH(hash, src->abs);
>>> + hash = HASH(hash, src->negate);
>>> +
>>> + for (unsigned i = 0; i < num_components; i++)
>>> + hash = HASH(hash, src->swizzle[i]);
>>> +
>>> + hash = hash_src(hash, &src->src);
>>> + return hash;
>>> +}
>>> +
>>> +static uint32_t
>>> +hash_alu(uint32_t hash, const nir_alu_instr *instr)
>>> +{
>>> + hash = HASH(hash, instr->op);
>>> + hash = HASH(hash, instr->dest.dest.ssa.num_components);
>>
>> Why are you hasing the dest.ssa.num_components instead of the
>> writemask? They should be the same in any case, but this seems a bit
>> out-of-place.
>
> No particular reason. I can change it if you want.
>
>>
>>> +
>>> + if (nir_op_infos[instr->op].algebraic_properties & NIR_OP_IS_COMMUTATIVE) {
>>> + assert(nir_op_infos[instr->op].num_inputs == 2);
>>> + uint32_t hash0 = hash_alu_src(hash, &instr->src[0],
>>> + nir_ssa_alu_instr_src_components(instr, 0));
>>> + uint32_t hash1 = hash_alu_src(hash, &instr->src[1],
>>> + nir_ssa_alu_instr_src_components(instr, 1));
>>> + /* For commutative operations, we need some commutative way of
>>> + * combining the hashes. One option would be to XOR them but that
>>> + * means that anything with two identical sources will hash to 0 and
>>> + * that's common enough we probably don't want the guaranteed
>>> + * collision. Either addition or multiplication will also work.
>>> + */
>>> + hash = hash0 * hash1;
>>> + } else {
>>> + for (unsigned i = 0; i < nir_op_infos[instr->op].num_inputs; i++) {
>>> + hash = hash_alu_src(hash, &instr->src[i],
>>> + nir_ssa_alu_instr_src_components(instr, i));
>>> + }
>>> + }
>>> +
>>> + return hash;
>>> +}
>>> +
>>> +static uint32_t
>>> +hash_load_const(uint32_t hash, const nir_load_const_instr *instr)
>>> +{
>>> + hash = HASH(hash, instr->def.num_components);
>>> +
>>> + hash = _mesa_fnv32_1a_accumulate_block(hash, instr->value.f,
>>> + instr->def.num_components
>>> + * sizeof(instr->value.f[0]));
>>> +
>>> + return hash;
>>> +}
>>> +
>>> +static int
>>> +cmp_phi_src(const void *data1, const void *data2)
>>> +{
>>> + const nir_phi_src *src1 = data1, *src2 = data2;
>>> + return src1->pred->index - src2->pred->index;
>>> +}
>>> +
>>> +static uint32_t
>>> +hash_phi(uint32_t hash, const nir_phi_instr *instr)
>>> +{
>>> + hash = HASH(hash, instr->instr.block);
>>> +
>>> + /* sort sources by predecessor index, since the order shouldn't matter */
>>> + unsigned num_preds = instr->instr.block->predecessors->entries;
>>> + nir_phi_src *srcs = malloc(num_preds * sizeof(nir_phi_src));
>>
>> You could use NIR_VLA and put it on the stack. That'd probably be more
>> efficient. Also, why are you copying the entire source and not just
>> making a list of pointers?
>
> Good point. It does prevent a pointer dereference when comparing, but
> that's probably less expensive than copying the entire thing when
> swapping.
>
>>
>>> + unsigned i = 0;
>>> + nir_foreach_phi_src(instr, src) {
>>> + srcs[i++] = *src;
>>> + }
>>> + qsort(srcs, num_preds, sizeof(nir_phi_src), cmp_phi_src);
>>
>> Sorting seems like as good a way as any. Another option would be to
>> do like we do for commutative ALU ops and multiply. Might be more
>> efficient but it probably doesn't matter too much.
>
> Perhaps, although sorting seems safer, since it's closer to how the
> hash is supposed to be used. For example, one thing hashing to 0 will
> make everything hash to 0, and I suspect there might be other problems
> where things aren't getting mixed as well -- which is more of a issue
> when combining more than 2 things, although it's not great for
> combining sources either.
I think it's fairly unlikely that we'll actually have something hash
to zero, especially given that we're hashing block indices in there as
well. I think the added hash-table scratching resulting from such a
collision is probably less expensive than all this copying, an
external library call, and a quick sort. Then again, we have no data
so we're just throwing darts at the wall and claiming to be closer to
the unmarked bulls-eye than the other. :-)
Which makes me wonder, why are we hashing the index and not the pointer?
>>
>>> + for (i = 0; i < num_preds; i++) {
>>> + hash = hash_src(hash, &srcs[i].src);
>>> + hash = HASH(hash, srcs[i].pred);
>>> + }
>>> + free(srcs);
>>> +
>>> + return hash;
>>> +}
>>> +
>>> +static uint32_t
>>> +hash_intrinsic(uint32_t hash, const nir_intrinsic_instr *instr)
>>> +{
>>> + const nir_intrinsic_info *info = &nir_intrinsic_infos[instr->intrinsic];
>>> + hash = HASH(hash, instr->intrinsic);
>>> +
>>> + if (info->has_dest)
>>> + hash = HASH(hash, instr->dest.ssa.num_components);
>>> +
>>> + assert(info->num_variables == 0);
>>> +
>>> + hash = _mesa_fnv32_1a_accumulate_block(hash, instr->const_index,
>>> + info->num_indices
>>> + * sizeof(instr->const_index[0]));
>>> + return hash;
>>> +}
>>> +
>>> +static uint32_t
>>> +hash_tex(uint32_t hash, const nir_tex_instr *instr)
>>> +{
>>> + hash = HASH(hash, instr->op);
>>> + hash = HASH(hash, instr->num_srcs);
>>> +
>>> + for (unsigned i = 0; i < instr->num_srcs; i++) {
>>> + hash = HASH(hash, instr->src[i].src_type);
>>> + hash = hash_src(hash, &instr->src[i].src);
>>> + }
>>> +
>>> + hash = HASH(hash, instr->coord_components);
>>> + hash = HASH(hash, instr->sampler_dim);
>>> + hash = HASH(hash, instr->is_array);
>>> + hash = HASH(hash, instr->is_shadow);
>>> + hash = HASH(hash, instr->is_new_style_shadow);
>>> + hash = HASH(hash, instr->const_offset);
>>> + unsigned component = instr->component;
>>> + hash = HASH(hash, component);
>>> + hash = HASH(hash, instr->sampler_index);
>>> + hash = HASH(hash, instr->sampler_array_size);
>>> +
>>> + assert(!instr->sampler);
>>> +
>>> + return hash;
>>> +}
>>> +
>>> +/* Computes a hash of an instruction for use in a hash table. Note that this
>>> + * will only work for instructions where instr_can_rewrite() returns true, and
>>> + * it should return identical hashes for two instructions that are the same
>>> + * according nir_instrs_equal().
>>> + */
>>> +
>>> +static uint32_t
>>> +hash_instr(const void *data)
>>> +{
>>> + const nir_instr *instr = data;
>>> + uint32_t hash = _mesa_fnv32_1a_offset_bias;
>>> +
>>> + switch (instr->type) {
>>> + case nir_instr_type_alu:
>>> + hash = hash_alu(hash, nir_instr_as_alu(instr));
>>> + break;
>>> + case nir_instr_type_load_const:
>>> + hash = hash_load_const(hash, nir_instr_as_load_const(instr));
>>> + break;
>>> + case nir_instr_type_phi:
>>> + hash = hash_phi(hash, nir_instr_as_phi(instr));
>>> + break;
>>> + case nir_instr_type_intrinsic:
>>> + hash = hash_intrinsic(hash, nir_instr_as_intrinsic(instr));
>>> + break;
>>> + case nir_instr_type_tex:
>>> + hash = hash_tex(hash, nir_instr_as_tex(instr));
>>> + break;
>>> + default:
>>> + unreachable("Invalid instruction type");
>>> + }
>>> +
>>> + return hash;
>>> +}
>>> +
>>> bool
>>> nir_srcs_equal(nir_src src1, nir_src src2)
>>> {
>>> @@ -66,6 +238,12 @@ nir_alu_srcs_equal(const nir_alu_instr *alu1, const nir_alu_instr *alu2,
>>> return nir_srcs_equal(alu1->src[src1].src, alu2->src[src2].src);
>>> }
>>>
>>> +/* Returns "true" if two instructions are equal. Note that this will only
>>> + * work for the subset of instructions defined by instr_can_rewrite(). Also,
>>> + * it should only return "true" for instructions that hash_instr() will return
>>> + * the same hash for (ignoring collisions, of course).
>>> + */
>>> +
>>> bool
>>> nir_instrs_equal(const nir_instr *instr1, const nir_instr *instr2)
>>> {
>>> @@ -204,3 +382,136 @@ nir_instrs_equal(const nir_instr *instr1, const nir_instr *instr2)
>>> return false;
>>> }
>>>
>>> +static bool
>>> +src_is_ssa(nir_src *src, void *data)
>>> +{
>>> + (void) data;
>>> + return src->is_ssa;
>>> +}
>>> +
>>> +static bool
>>> +dest_is_ssa(nir_dest *dest, void *data)
>>> +{
>>> + (void) data;
>>> + return dest->is_ssa;
>>> +}
>>> +
>>> +/* This function determines if uses of an instruction can safely be rewritten
>>> + * to use another identical instruction instead. Note that this function must
>>> + * be kept in sync with hash_instr() and nir_instrs_equal() -- only
>>> + * instructions that pass this test will be handed on to those functions, and
>>> + * conversely they must handle everything that this function returns true for.
>>> + */
>>> +
>>> +static bool
>>> +instr_can_rewrite(nir_instr *instr)
>>> +{
>>> + /* We only handle SSA. */
>>> + if (!nir_foreach_dest(instr, dest_is_ssa, NULL) ||
>>> + !nir_foreach_src(instr, src_is_ssa, NULL))
>>> + return false;
>>> +
>>> + switch (instr->type) {
>>> + case nir_instr_type_alu:
>>> + case nir_instr_type_load_const:
>>> + case nir_instr_type_phi:
>>> + return true;
>>> + case nir_instr_type_tex: {
>>> + nir_tex_instr *tex = nir_instr_as_tex(instr);
>>> +
>>> + /* Don't support un-lowered sampler derefs currently. */
>>> + if (tex->sampler)
>>> + return false;
>>> +
>>> + return true;
>>> + }
>>> + case nir_instr_type_intrinsic: {
>>> + const nir_intrinsic_info *info =
>>> + &nir_intrinsic_infos[nir_instr_as_intrinsic(instr)->intrinsic];
>>> + return (info->flags & NIR_INTRINSIC_CAN_ELIMINATE) &&
>>> + (info->flags & NIR_INTRINSIC_CAN_REORDER) &&
>>> + info->num_variables == 0; /* not implemented yet */
>>> + }
>>> + case nir_instr_type_call:
>>> + case nir_instr_type_jump:
>>> + case nir_instr_type_ssa_undef:
>>> + return false;
>>> + case nir_instr_type_parallel_copy:
>>> + default:
>>> + unreachable("Invalid instruction type");
>>> + }
>>> +
>>> + return false;
>>> +}
>>> +
>>> +static nir_ssa_def *
>>> +nir_instr_get_dest_ssa_def(nir_instr *instr)
>>> +{
>>> + switch (instr->type) {
>>> + case nir_instr_type_alu:
>>> + assert(nir_instr_as_alu(instr)->dest.dest.is_ssa);
>>> + return &nir_instr_as_alu(instr)->dest.dest.ssa;
>>> + case nir_instr_type_load_const:
>>> + return &nir_instr_as_load_const(instr)->def;
>>> + case nir_instr_type_phi:
>>> + assert(nir_instr_as_phi(instr)->dest.is_ssa);
>>> + return &nir_instr_as_phi(instr)->dest.ssa;
>>> + case nir_instr_type_intrinsic:
>>> + assert(nir_instr_as_intrinsic(instr)->dest.is_ssa);
>>> + return &nir_instr_as_intrinsic(instr)->dest.ssa;
>>> + case nir_instr_type_tex:
>>> + assert(nir_instr_as_tex(instr)->dest.is_ssa);
>>> + return &nir_instr_as_tex(instr)->dest.ssa;
>>> + default:
>>> + unreachable("We never ask for any of these");
>>> + }
>>> +}
>>> +
>>> +static bool
>>> +cmp_func(const void *data1, const void *data2)
>>> +{
>>> + return nir_instrs_equal(data1, data2);
>>> +}
>>> +
>>> +struct set *
>>> +nir_instr_set_create(void *mem_ctx)
>>> +{
>>> + return _mesa_set_create(mem_ctx, hash_instr, cmp_func);
>>> +}
>>> +
>>> +void
>>> +nir_instr_set_destroy(struct set *instr_set)
>>> +{
>>> + _mesa_set_destroy(instr_set, NULL);
>>> +}
>>> +
>>> +bool
>>> +nir_instr_set_add_or_rewrite(struct set *instr_set, nir_instr *instr)
>>> +{
>>> + if (!instr_can_rewrite(instr))
>>> + return false;
>>> +
>>> + struct set_entry *entry = _mesa_set_search(instr_set, instr);
>>> + if (entry) {
>>> + nir_ssa_def *def = nir_instr_get_dest_ssa_def(instr);
>>> + nir_ssa_def *new_def =
>>> + nir_instr_get_dest_ssa_def((nir_instr *) entry->key);
>>> + nir_ssa_def_rewrite_uses(def, nir_src_for_ssa(new_def));
>>> + return true;
>>> + }
>>> +
>>> + _mesa_set_add(instr_set, instr);
>>> + return false;
>>> +}
>>> +
>>> +void
>>> +nir_instr_set_remove(struct set *instr_set, nir_instr *instr)
>>> +{
>>> + if (!instr_can_rewrite(instr))
>>> + return;
>>> +
>>> + struct set_entry *entry = _mesa_set_search(instr_set, instr);
>>> + if (entry)
>>> + _mesa_set_remove(instr_set, entry);
>>> +}
>>> +
>>> diff --git a/src/glsl/nir/nir_instr_set.h b/src/glsl/nir/nir_instr_set.h
>>> index f5baffa..a7f6c9d 100644
>>> --- a/src/glsl/nir/nir_instr_set.h
>>> +++ b/src/glsl/nir/nir_instr_set.h
>>> @@ -27,3 +27,38 @@
>>>
>>> bool nir_instrs_equal(const nir_instr *instr1, const nir_instr *instr2);
>>>
>>> +/**
>>> + * This file defines functions for creating, destroying, and manipulating an
>>> + * "instruction set," which is an abstraction for finding duplicate
>>> + * instructions using a hash set. Note that the question of whether an
>>> + * instruction is actually a duplicate (e.g. whether it has any side effects)
>>> + * is handled transparently. The user can pass any instruction to
>>> + * nir_instr_set_add_or_rewrite() and nir_instr_set_remove(), and if the
>>> + * instruction isn't safe to rewrite or isn't supported, it's silently
>>> + * removed.
>>> + */
>>> +
>>> +/*@{*/
>>> +
>>> +/** Creates an instruction set, using a given ralloc mem_ctx */
>>> +struct set *nir_instr_set_create(void *mem_ctx);
>>> +
>>> +/** Destroys an instruction set. */
>>> +void nir_instr_set_destroy(struct set *instr_set);
>>> +
>>> +/**
>>> + * Adds an instruction to an instruction set if it doesn't exist, or if it
>>> + * does already exist, rewrites all uses of it to point to the other
>>> + * already-inserted instruction. Returns 'true' if the uses of the instruction
>>> + * were rewritten.
>>> + */
>>> +bool nir_instr_set_add_or_rewrite(struct set *instr_set, nir_instr *instr);
>>> +
>>> +/**
>>> + * Removes an instruction from an instruction set, so that other instructions
>>> + * won't be merged with it.
>>> + */
>>> +void nir_instr_set_remove(struct set *instr_set, nir_instr *instr);
>>> +
>>> +/*@}*/
>>> +
>>> --
>>> 2.1.0
>>>
>>> _______________________________________________
>>> mesa-dev mailing list
>>> mesa-dev at lists.freedesktop.org
>>> http://lists.freedesktop.org/mailman/listinfo/mesa-dev
More information about the mesa-dev
mailing list