This reverts commit a4031bdfa9. It's
redundant with the sample mask predication done at this point by the
common logical send lowering infrastructure, and rather buggy because
it wasn't applying the correct sample mask in shaders using discard,
since the dispatch mask returned by FS_OPCODE_MOV_DISPATCH_TO_FLAGS
doesn't reflect samples discarded by the shader, so it could have led
to data corruption in fragment shader invocations that execute discard
based on a non-dynamically uniform condition.
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
The introduction of 16-bit types with VK_KHR_16bit_storages implies that
push constant offsets could be multiple of 2-bytes. Some assertions are
updated so offsets should be just multiple of size of the base type but
in some cases we can not assume it as doubles aren't aligned to 8 bytes
in some cases.
For 16-bit types, the push constant offset takes into account the
internal offset in the 32-bit uniform bucket adding 2-bytes when we access
not 32-bit aligned elements. In all 32-bit aligned cases it just becomes 0.
v2: Assert offsets to be aligned to the dest type size. (Jason Ekstrand)
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Restrict the use of untyped_surface_write with 16-bit pairs in
ssbo to the cases where we can guarantee that offset is multiple
of 4.
Taking into account that VK_KHR_relaxed_block_layout is available
in ANV we can only guarantee that when we have a constant offset
that is multiple of 4. For non constant offsets we will always use
byte_scattered_write.
v2: (Jason Ekstrand)
- Assert offset_reg to be multiple of 4 if it is immediate.
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
16-bit load_ubo/ssbo operations that call do_untyped_read_vector don't
guarantee that offsets are multiple of 4-bytes as required by untyped_read
message. This happens for example in the case of f16mat3x3 when then
VK_KHR_relaxed_block_layout is enabled.
Vectors reads when we have non-constant offsets are implemented with
multiple byte_scattered_read messages that not require 32-bit aligned offsets.
Now for all constant offsets we can use the untyped_read_surface message.
In the case of constant offsets not aligned to 32-bits, we calculate a
start offset 32-bit aligned and use the shuffle_32bit_load_result_to_16bit_data
function and the first_component parameter to skip the copy of the unneeded
component.
v2: (Jason Ekstrand)
Use untyped_read_surface messages always we have constant offsets.
v3: (Jason Ekstrand)
Simplify loop for reads with non constant offsets.
Use end - start to calculate the number of 32-bit components to read with
constant offsets.
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
This helper used to load 16bit components from 32-bits read now allows
skipping components with the new parameter first_component. The semantics
now skip components until we reach the first_component, and then reads the
number of components passed to the function.
All previous uses of the helper are updated to use 0 as first_component.
This will allow read 16-bit components when the first one is not aligned
32-bit. Enabling more usages of untyped_reads with 16-bit types.
v2: (Jason Ektrand)
Change parameters order to first_component, num_components
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
The surfaces that backup the GPU buffers have a boundary check that
considers that access to partial dwords are considered out-of-bounds.
For example, buffers with 1,3 16-bit elements has size 2 or 6 and the
last two bytes would always be read as 0 or its writting ignored.
The introduction of 16-bit types implies that we need to align the size
to 4-bytew multiples so that partial dwords could be read/written.
Adding an inconditional +2 size to buffers not being multiple of 2
solves this issue for the general cases of UBO or SSBO.
But, when unsized arrays of 16-bit elements are used it is not possible
to know if the size was padded or not. To solve this issue the
implementation calculates the needed size of the buffer surfaces,
as suggested by Jason:
surface_size = isl_align(buffer_size, 4) +
(isl_align(buffer_size, 4) - buffer_size)
So when we calculate backwards the buffer_size in the backend we
update the resinfo return value with:
buffer_size = (surface_size & ~3) - (surface_size & 3)
It is also exposed this buffer requirements when robust buffer access
is enabled so these buffer sizes recommend being multiple of 4.
v2: (Jason Ekstrand)
Move padding logic fron anv to isl_surface_state.
Move calculus of original size from spirv to driver backend.
v3: (Jason Ekstrand)
Rename some variables and use a similar expresion when calculating.
padding than when obtaining the original buffer size.
Avoid use of unnecesary component call at brw_fs_nir.
v4: (Jason Ekstrand)
Complete comment with buffer size calculus explanation in brw_fs_nir.
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
This code to re-set the type of the source and destination is not
necessary since we never manipulate the types. Looks like a
left over from a time where we had to retype to float temporarily
to handle 64-bit inputs.
Reviewed-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com>
Divide it by two as we do for other stages. This is because the
component layout qualifier is always in 32-bit units.
Fixes issues in a new CTS test (still WIP):
KHR-GL45.enhanced_layouts.varying_double_components
Reviewed-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com>
Gen 10 has a strange hardware bug involving V immediates with W types.
It appears that a mov(8) g2<1>W 0x76543210V will actually result in g2
getting the value {3, 2, 1, 0, 3, 2, 1, 0}. In particular, the bottom
four nibbles are repeated instead of the top four being taken. (A mov
of 0x00003210V yields the same result.) This bug does not appear in any
hardware documentation as far as we can tell and the simulator does not
implement the bug either.
Commit 6132992cdb was mostly a no-op
except that it changed the type of the subgroup invocation from UW to W
and caused us to tickle this bug with basically every compute shader
that uses any sort of invocation ID (which is most of them). This is
also potentially an issue for geometry shader input pulls and SampleID
setup. The easy solution is just to change the few places where we use
a vector integer immediate with a W type to use a UW type.
Reviewed-by: Matt Turner <mattst88@gmail.com>
Cc: mesa-stable@lists.freedesktop.org
Fixes: 6132992cdb
SSBO loads were using byte_scattered read messages as they allow
reading 16-bit size components. byte_scattered messages can only
operate one component at a time so we needed to emit as many messages
as components.
But for vec2 and vec4 of 16-bit, being multiple of 32-bit we can use the
untyped_surface_read message to read pairs of 16-bit components using only
one message. Once each pair is read it is unshuffled to return the proper
16-bit components. vec3 case is assimilated to vec4 but the 4th component
is ignored.
16-bit scalars are read using one byte_scattered_read message.
v2: Removed use of stride = 2 on sources (Jason Ekstrand)
Rework optimization using unshuffle 16 reads (Chema Casanova)
v3: Use W and D types insead of HF and F in shuffle to avoid rounding
erros (Jason Ekstrand)
Use untyped_surface_read for 16-bit vec3. (Jason Ekstrand)
v4: Use subscript insead of chaging type and stride (Jason Ekstrand)
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Currently, we use byte-scattered write messages for storing 16-bit
into an SSBO. This is because untyped surface messages have a fixed
32-bit size.
This patch optimizes these 16-bit writes by combining 2 values (e.g,
two consecutive components aligned with 32-bits) into a 32-bit register,
packing the two 16-bit words.
16-bit single component values will continue to use byte-scattered
write messages. The same will happens when the first consecutive
component is not aligned 32-bits.
This optimization reduces the number of SEND messages used for storing
16-bit values potentially by 2 or 4, which cuts down execution time
significantly because byte-scattered writes are an expensive
operation as they only write a component for message.
v2: Removed use of stride = 2 on sources (Jason Ekstrand)
Rework optimization using shuffle 16 write and enable writes
of 16bit vec4 with only one message of 32-bits. (Chema Casanova)
v3: - Fix coding style (Eduardo Lima)
- Reorganize code to avoid duplication. (Jason Ekstrand)
- Include new comments to explain the length calculations to
fix alignment issues of components. (Jason Ekstrand)
- Fix issues with writemask yz with 16-bit writes. (Jason Ektrand)
v4: (Jason Ekstrand)
- Reorganize 64-bit ssbo-writes to avoid using slots_per_component.
- Comment about why suffle is needed when using byte_scattered_write.
Signed-off-by: Eduardo Lima <elima@igalia.com>
Signed-off-by: Jose Maria Casanova Crespo <jmcasanova@igalia.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
This helpers are used to load/store 16-bit types from/to 32-bit
components.
The functions shuffle_32bit_load_result_to_16bit_data and
shuffle_16bit_data_for_32bit_write are implemented in a similar
way than the analogous functions for handling 64-bit types.
v1: Explain need of temporary in shuffle operations. (Jason Ekstrand)
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Used to enable 16-bit reads at do_untyped_vector_read, that is used on
the following intrinsics:
* nir_intrinsic_load_shared
* nir_intrinsic_load_ssbo
v2: Removed use of stride = 2 on 16-bit sources (Jason Ekstrand)
v3: - Add bitsize to scattered read operation (Jason Ekstrand)
- Remove implementation of 16-bit UBO read from this patch.
- Avoid assertion at opt_algebraic caused by ADD of two IMM with
offset with BRW_REGISTER_TYPE_UD type found on matrix tests.
(Jose Maria Casanova)
v4: (Jason Ekstrand)
- Put if case for 16-bits at the beginning of the if ladder.
- Use type_sz(dest.type) * 8 as bit_size parameter for scattered read.
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
While on Untyped Surface messages the bits of the execution mask are
ANDed with the corresponding bits of the Pixel/Sample Mask, that is
not the case for byte scattered writes. That is needed to avoid ssbo
stores writing on helper invocations. So when that can affect, we load
the sample mask, and predicate the send message.
Note: the need for this patch was tested with a custom test. Right now
the 16 bit storage CTS tests doesnt need this path in order to get a
full pass.
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
We need to rely on byte scattered writes as untyped writes are 32-bit
size. We could try to keep using 32-bit messages when we have two or
four 16-bit elements, but for simplicity sake, we use the same message
for any component number. We revisit this aproach in the follwing
patches.
v2: Removed use of stride = 2 on 16-bit sources (Jason Ekstrand)
v3: (Jason Ekstrand)
- Include bit_size to scattered write message and remove namespace
- specific for scattered messages.
- Move comment to proper place.
- Squashed with i965/fs: Adjust type_size/type_slots on store_ssbo.
(Jose Maria Casanova)
- Take into account that get_nir_src returns now WORD types for
16-bit sources instead of DWORD.
v4: (Jason Ekstrand)
- Rename lenght variable to num_components.
- Include assertions before emit_untyped_write.
- Remove type_slot in favor of num_slot and first_slot.
Signed-off-by: Jose Maria Casanova Crespo <jmcasanova@igalia.com>
Signed-off-by: Alejandro Piñeiro <apinheiro@igalia.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
By default we don't set the rounding mode. We only set
round-to-near-even or round-to-zero mode if explicitly set from nir.
v2: Use a single SHADER_OPCODE_RND_MODE opcode taking an immediate
with the rounding mode (Curro)
v3: Use new helper brw_rnd_mode_from_nir_op (Jason Ekstrand)
Signed-off-by: Jose Maria Casanova Crespo <jmcasanova@igalia.com>
Signed-off-by: Alejandro Piñeiro <apinheiro@igalia.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Conversions to 16-bit need having aligment between the 16-bit
and 32-bit types. So the conversion operations unpack 16-bit types
to with an stride=2 and then applies a MOV with the conversion.
v2 (Jason Ekstrand):
- Avoid the general use of stride=2 for 16-bit register types.
v3 (Topi Pohjolainen)
- Code style fix
(Jason Ekstrand)
- Now nir_op_f2f16 was renamed to nir_op_f2f16_undef
because conversion to f16 with undefined rounding is explicit
Signed-off-by: Eduardo Lima <elima@igalia.com>
Signed-off-by: Alejandro Piñeiro <apinheiro@igalia.com>
Signed-off-by: Jose Maria Casanova Crespo <jmcasanova@igalia.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
We use the same hardware mechanism for both atomic counters and SSBO
atomics, so there's really no benefit to maintaining separate code to
handle each case. Instead, we can just use Rob's shiny new NIR pass to
convert atomic_uints to SSBOs, and delete piles of code.
The ssbo_start section of the binding table becomes a combined ABO and
SSBO section, with ABOs first, then SSBOs.
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
The MOV instruction can extract bytes to words/double words, and
words/double words to quadwords, but not byte to quadwords.
For unsigned byte to quadword, we can read them as words and AND off the
high byte and extract to quadword in one instruction. For signed bytes,
we need to first sign extend to word and the sign extend that word to a
quadword.
Fixes the following test on CHV, BXT, and GLK:
KHR-GL46.shader_ballot_tests.ShaderBallotBitmasks
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=103628
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Fixes the following tests on CHV, BXT, and GLK:
KHR-GL46.shader_ballot_tests.ShaderBallotFunctionBallot
dEQP-VK.spirv_assembly.instruction.compute.uconvert.uint32_to_int64
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=103115
The GL_ARB_shader_ballot spec says that gl_SubGroupSizeARB is declared
as a uniform. This means that it cannot change across an invocation
such as a draw call or a compute dispatch. For compute shaders, we're
ok because we only ever use one dispatch size. For fragment, however,
the hardware dynamically chooses between SIMD8 and SIMD16 which violates
the spec. Instead, let's just pick a subgroup size based on the shader
stage. The fixed size we choose for compute shaders is a bit higher
than strictly needed but there's no real harm in that. The advantage is
that, if they do anything interesting with the value, NIR will see it as
an immediate and can optimize better.
Acked-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Subgroup invocation is computed using a vector immediate and some
dispatch-aware arithmetic. Unfortunately, due to the vector arithmetic,
and the fact that it's frequently read 16-wide, it's not something that
can easily be CSEd by the back-end compiler. There are a few different
possible approaches to this problem:
1) Emit the code to calculate the subgroup invocation on-the-fly and
trust NIR to do the CSE. This is what we were doing.
2) Add a back-end instruction for the subgroup ID. This has the
advantage of helping the back-end compiler with CSE but has the
downside of very poor scheduling for the calculation because it has
to be emitted in the back-end.
3) Emit the calculation at the top of the program and re-use the
result. This gets rid of the CSE problem but comes at the cost of
an extra live register.
This commit switches us from 1) to 3). We choose to store the subgroup
invocation values as a W type to reduce the impact of the extra live
register. Trusting NIR and using 1) was fine but we're soon going to
want to use the subgroup invocation value for other things in the
back-end compiler and this makes it much easier to do without having to
worry about CSE problems.
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
We're going to want subgroup ID for SPIR-V subgroups eventually anyway.
We really only want to push one and calculate the other from it. It
makes a bit more sense to push the subgroup ID because it's simpler to
calculate and because it's a real API thing. The only advantage to
pushing the base thread ID is to avoid a single SHL in the shader.
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Previously, brw_nir_lower_intrinsics added the param and then emitted a
load_uniform intrinsic to load it directly. This commit switches things
over to use a specific NIR intrinsic for the thread id. The one thing I
don't like about this approach is that we have to copy thread_local_id
over to the new visitor in import_uniforms.
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Before, we bailing in assign_constant_locations based on the minimum
dispatch size. The more direct thing to do is simply to check for
whether or not we have constant locations and bail if we do. For
nir_setup_uniforms, it's completely safe to do it multiple times because
we just copy a value from the NIR shader.
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
This is what we really wanted all along. Always retyping to D works
because that's what get_nir_src() always gives us, at least for 32-bit
types. The SPIR-V variants of these operations accept arbitrary types
and we need this if we're going to handle 64 or 16-bit values.
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
The index is any value provided by the shader and this can be called in
non-uniform control flow so we can't just take component 0. Found by
inspection.
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Stop retyping the output of shuffle_64bit_data_for_32bit_write. It's
always BRW_REGISTER_TYPE_D which is perfectly fine for writing out.
Also, when we change get_nir_src to return something with a 64-bit type
for 64-bit values, the retyping will not be at all what we want. Also,
retyping the output based on src.type before we whack it back to 32 bits
is a problem because the output is always 32 bits.
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
All callers of this function allocate a fs_reg expressly to pass into
it. It's much easier if we just let the helper allocate the register.
While we're here, we switch it to doing the MOVs with an integer type so
that we don't accidentally canonicalize floats on half of a double.
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
The swizzles weren't doing any good because swiz is just XYZW. Also, we
were emitting an extra set of MOVs because shuffle_64bit_data_for_32bit
already does a MOV for us. Finally, the temporary was only ever used
inside the inner loop so there's no need for it to actually be an array.
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
For some reason, the any/all predicates don't work properly with SIMD32.
In particular, it appears that a SEL with a QtrCtrl of 2H doesn't read
the correct subset of the flag register and you end up getting garbage
in the second half. Work around this by using a pair of 1-wide MOVs and
scattering the result. This fixes the any/all instructions for SIMD32.
Reviewed-by: Matt Turner <mattst88@gmail.com>
Cc: mesa-stable@lists.freedesktop.org
The any/all intrinsics return a boolean value so D or UD is the correct
type. Unfortunately, get_nir_dest has the annoying behavior of
returnning a float type by default. This causes format conversion which
gives us -1.0f or 0.0f in the register. If the consumer of the result
does an integer comparison to zero, it will give you the right boolean
value but if we do something more clever based on the 0/~0 assumption
for booleans, this will give the wrong value.
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Cc: mesa-stable@lists.freedesktop.org
In fragment shaders f0.1 is used for discards so doing ballot after a
discard can potentially cause the discard to not happen. However, we
don't support SIMD32 fragment shaders yet so this isn't a problem.
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Cc: mesa-stable@lists.freedesktop.org
We have ANY/ALL32 predicates and, for the most part, they work just
fine. (See the next commit for more details.) Also, due to the way
that flag registers are handled in hardware, instruction splitting is
able to split the CMP correctly. Specifically, that hardware looks at
the execution group and knows to shift it's flag usage up correctly so a
2H instruction will write to f0.1 instead of f0.0.
Reviewed-by: Matt Turner <mattst88@gmail.com>
Cc: mesa-stable@lists.freedesktop.org
Returns the brw_type for a given ssa.bit_size, and a reference type.
So if bit_size is 64, and the reference type is BRW_REGISTER_TYPE_F,
it returns BRW_REGISTER_TYPE_DF. The same applies if bit_size is 32
and reference type is BRW_REGISTER_TYPE_HF it returns BRW_REGISTER_TYPE_F
v2 (Jason Ekstrand):
- Use better unreachable() messages
- Add Q types
Signed-off-by: Jose Maria Casanova Crespo <jmcasanova@igalia.com>
Signed-off-by: Alejandro Piñeiro <apinheiro@igalia.com
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
ARB_enhanced_layouts allows multiple output variables to share the same
location - and these variables may not have the same sizes. For
example, consider these output variables:
// consume X/Y/Z components of 6 vectors
layout(location = 0) out vec3 a[6];
// consumes W component of the first vector
layout(location = 0, component = 3) out float b;
Looking at the first declaration, we see that VARYING_SLOT_VAR0 needs 24
components worth of space (vec3 padded out to a vec4, 4 * 6 = 24). But
looking at the second declaration, we would think that VARYING_SLOT_VAR0
needs only 4 components of space (a single float padded out to a vec4).
nir_setup_outputs() only considered the space requirements of the first
declaration it happened to see, so if 'float b' came first, it would
underallocate the output register space, causing brw_fs_validator.cpp
to assert fail about inst->dst.offset exceeding the register size.
Fixes Piglit's tests/spec/arb_enhanced_layouts/execution/component-layout/
vs-to-fs-array-interleave-single-location.shader_test.
Thanks to Tim Arceri for finding this bug and writing a test!
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
When computing the total size of the URB for tessellation evaluation
inputs we were not accounting for this, and instead we were always
assuming that each input would take a single vec4 slot, which could
lead to computing a smaller read size than required. Specifically, this
is a problem when the last input is a dvec3/4 such that its XY components
are stored in the the second half of a payload register (which can happen
if the offset for the input in the URB is not 64-bit aligned because
there are 32-bit inputs mixed in) and the ZW components in the
first half of the next, as in this case we would fail to account for the
extra slot required for the ZW components.
Fixes (requires another fix in CTS currently in review):
KHR-GL45.enhanced_layouts.varying_locations
KHR-GL45.enhanced_layouts.varying_array_locations
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
... without the float -> double conversion. Low power parts have
additional restrictions when it comes to operating on 64-bit types, and
the instruction used to do the conversion violates one of them:
specifically, the restriction that "Source and Destination horizontal
stride must be aligned to the same qword".
Previously we generated a float and then converted, but we can avoid the
conversion by using the same extract-the-sign-bit + or-in-1.0 algorithm
by directly operating on the high four bytes of each double-precision
component in the result.
In SIMD8 and SIMD16 this cuts one instruction from the implementation,
and more importantly that instruction is the one which violated the
regioning restriction.
Along the way I removed some comments that I did not think helped, and
some code about double comparisons which does not seem to be necessary
today.
This prevents validation failures caught by the new EU validation code
added in later patches.
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
64-bit operations on Atom parts have additional restrictions over their
big-core counterparts (validated by later patches).
Specifically, the restriction that "Source and Destination horizontal
stride must be aligned to the same qword" is violated by most shift
operations since NIR uses a 32-bit value as the shift count argument,
and this causes instructions like
shl(8) g19<1>Q g5<4,4,1>Q g23<4,4,1>UD
where src1 has a 32-bit stride, but the dest and src0 have a 64-bit
stride.
This caused ~4 pixels in the ARB_shader_ballot piglit test
fs-readInvocation-uint.shader_test to be incorrect. Unfortunately no
ARB_gpu_shader_int64 test hit this case because they operate on
uniforms, and their scalar regions are an exception to the restriction.
We work around this by effectively unpacking the shift count, so that we
can read it with a 64-bit stride in the shift instruction. Unfortunately
the unpack (a MOV with a dst stride of 2) is a partial write, and cannot
be copy-propagated or CSE'd.
Bugzilla: https://bugs.freedesktop.org/101984
Triggering the push model when 64-bit inputs are involved is not easy due to
the constrains on the maximum number of registers that we allow for this mode,
however, for GS with 'points' primitive type and just a couple of double
varyings we can trigger this and it just doesn't work because the
implementation is not 64-bit aware at all. For now, let's make sure that we
don't attempt this model whith 64-bit inputs and we always fall back to pull
model for them.
Also, don't enable the VUE handles in the thread payload on the fly when we
find an input for which we need the pull model, this is not safe: if we need
to resort to the pull model we need to account for that when we setup the
thread payload so we compute the first non-payload register properly. If we
didn't do that correctly and we enable it on-the-fly here then we will end up
VUE handles on the first non-payload register which will probably lead to
GPU hangs. Instead, always enable the VUE handles for the pull model so we
can safely use them when needed. The GS is going to resort to pull model
almost in every situation anyway, so this shouldn't make a significant
difference and it makes things easier and safer.
v2: Always enable the VUE handles for pull model, this is easier and safer
and the GS is going to fallback to pull model almost always anyway (Ken)
v3: Only clamp the URB read length if we are over the maximum reserved for
push inputs as we were doing in the original code (Ken).
v4: No need to clamp the urb read length if invocations > 1
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
