This is the implementation of https://github.com/bytecodealliance/wasmtime/issues/4155, using the "inverted API" approach suggested by @cfallin (thanks!) in Cranelift, and trait object to provide a backend for an all-included experience in Wasmtime.
After the suggestion of Chris, `Function` has been split into mostly two parts:
- on the one hand, `FunctionStencil` contains all the fields required during compilation, and that act as a compilation cache key: if two function stencils are the same, then the result of their compilation (`CompiledCodeBase<Stencil>`) will be the same. This makes caching trivial, as the only thing to cache is the `FunctionStencil`.
- on the other hand, `FunctionParameters` contain the... function parameters that are required to finalize the result of compilation into a `CompiledCode` (aka `CompiledCodeBase<Final>`) with proper final relocations etc., by applying fixups and so on.
Most changes are here to accomodate those requirements, in particular that `FunctionStencil` should be `Hash`able to be used as a key in the cache:
- most source locations are now relative to a base source location in the function, and as such they're encoded as `RelSourceLoc` in the `FunctionStencil`. This required changes so that there's no need to explicitly mark a `SourceLoc` as the base source location, it's automatically detected instead the first time a non-default `SourceLoc` is set.
- user-defined external names in the `FunctionStencil` (aka before this patch `ExternalName::User { namespace, index }`) are now references into an external table of `UserExternalNameRef -> UserExternalName`, present in the `FunctionParameters`, and must be explicitly declared using `Function::declare_imported_user_function`.
- some refactorings have been made for function names:
- `ExternalName` was used as the type for a `Function`'s name; while it thus allowed `ExternalName::Libcall` in this place, this would have been quite confusing to use it there. Instead, a new enum `UserFuncName` is introduced for this name, that's either a user-defined function name (the above `UserExternalName`) or a test case name.
- The future of `ExternalName` is likely to become a full reference into the `FunctionParameters`'s mapping, instead of being "either a handle for user-defined external names, or the thing itself for other variants". I'm running out of time to do this, and this is not trivial as it implies touching ISLE which I'm less familiar with.
The cache computes a sha256 hash of the `FunctionStencil`, and uses this as the cache key. No equality check (using `PartialEq`) is performed in addition to the hash being the same, as we hope that this is sufficient data to avoid collisions.
A basic fuzz target has been introduced that tries to do the bare minimum:
- check that a function successfully compiled and cached will be also successfully reloaded from the cache, and returns the exact same function.
- check that a trivial modification in the external mapping of `UserExternalNameRef -> UserExternalName` hits the cache, and that other modifications don't hit the cache.
- This last check is less efficient and less likely to happen, so probably should be rethought a bit.
Thanks to both @alexcrichton and @cfallin for your very useful feedback on Zulip.
Some numbers show that for a large wasm module we're using internally, this is a 20% compile-time speedup, because so many `FunctionStencil`s are the same, even within a single module. For a group of modules that have a lot of code in common, we get hit rates up to 70% when they're used together. When a single function changes in a wasm module, every other function is reloaded; that's still slower than I expect (between 10% and 50% of the overall compile time), so there's likely room for improvement.
Fixes#4155.
Ported the existing implementations of the following opcodes on AArch64
to ISLE:
- `AvgRound`
- Also introduced support for `i64x2` vectors, as per the docs.
- `SqmulRoundSat`
Copyright (c) 2022 Arm Limited
* Cranelift: Add instructions for getting the current stack/frame pointers and return address
This is the initial part of https://github.com/bytecodealliance/wasmtime/issues/4535
* x64: Remove `Amode::RbpOffset` and use `Amode::ImmReg` instead
We just special case getting operands from `Amode`s now.
* Fix s390x `get_return_address`; require `preserve_frame_pointers=true`
* Assert that `Amode::ImmRegRegShift` doesn't use rbp/rsp
* Handle non-allocatable registers in Amode::with_allocs
* Use "stack" instead of "r15" on s390x
* r14 is an allocatable register on s390x, so it shouldn't be used with `MovPReg`
* Cranellift: remove Baldrdash support and related features.
As noted in Mozilla's bugzilla bug 1781425 [1], the SpiderMonkey team
has recently determined that their current form of integration with
Cranelift is too hard to maintain, and they have chosen to remove it
from their codebase. If and when they decide to build updated support
for Cranelift, they will adopt different approaches to several details
of the integration.
In the meantime, after discussion with the SpiderMonkey folks, they
agree that it makes sense to remove the bits of Cranelift that exist
to support the integration ("Baldrdash"), as they will not need
them. Many of these bits are difficult-to-maintain special cases that
are not actually tested in Cranelift proper: for example, the
Baldrdash integration required Cranelift to emit function bodies
without prologues/epilogues, and instead communicate very precise
information about the expected frame size and layout, then stitched
together something post-facto. This was brittle and caused a lot of
incidental complexity ("fallthrough returns", the resulting special
logic in block-ordering); this is just one example. As another
example, one particular Baldrdash ABI variant processed stack args in
reverse order, so our ABI code had to support both traversal
orders. We had a number of other Baldrdash-specific settings as well
that did various special things.
This PR removes Baldrdash ABI support, the `fallthrough_return`
instruction, and pulls some threads to remove now-unused bits as a
result of those two, with the understanding that the SpiderMonkey folks
will build new functionality as needed in the future and we can perhaps
find cleaner abstractions to make it all work.
[1] https://bugzilla.mozilla.org/show_bug.cgi?id=1781425
* Review feedback.
* Fix (?) DWARF debug tests: add `--disable-cache` to wasmtime invocations.
The debugger tests invoke `wasmtime` from within each test case under
the control of a debugger (gdb or lldb). Some of these tests started to
inexplicably fail in CI with unrelated changes, and the failures were
only inconsistently reproducible locally. It seems to be cache related:
if we disable cached compilation on the nested `wasmtime` invocations,
the tests consistently pass.
* Review feedback.
* Allow 64-bit vectors and implement for interpreter
The AArch64 backend already supports 64-bit vectors; this simply allows
instructions to make use of that.
Implemented support for 64-bit vectors within the interpreter to allow
interpret runtests to use them.
Copyright (c) 2022 Arm Limited
* Disable 64-bit SIMD `iaddpairwise` tests on s390x
Copyright (c) 2022 Arm Limited
* cranelift: Restrict `br_table` to `i32` indices
In #4498 it was proposed that we should only accept `i32` indices
to `br_table`. The rationale for this is that larger types lead the
users to a false sense of flexibility (since we don't support jump
tables larger than u32's), and narrower types are not well tested
paths that would be safer if we removed them.
* cranelift: Reduce directly from i128 to i32 in Switch
Preserving frame pointers -- even inside leaf functions -- makes it easy to
capture the stack of a running program, without requiring any side tables or
metadata (like `.eh_frame` sections). Many sampling profilers and similar tools
walk frame pointers to capture stacks. Enabling this option will play nice with
those tools.
Introduce a new concept in the IR that allows a producer to create
dynamic vector types. An IR function can now contain global value(s)
that represent a dynamic scaling factor, for a given fixed-width
vector type. A dynamic type is then created by 'multiplying' the
corresponding global value with a fixed-width type. These new types
can be used just like the existing types and the type system has a
set of hard-coded dynamic types, such as I32X4XN, which the user
defined types map onto. The dynamic types are also used explicitly
to create dynamic stack slots, which have no set size like their
existing counterparts. New IR instructions are added to access these
new stack entities.
Currently, during codegen, the dynamic scaling factor has to be
lowered to a constant so the dynamic slots do eventually have a
compile-time known size, as do spill slots.
The current lowering for aarch64 just targets Neon, using a dynamic
scale of 1.
Copyright (c) 2022, Arm Limited.
* cranelift: Fix `bint` implementation on interpreter
The interpreter was returning -1 instead of 1 for positive values.
This also extends the bint test suite to cover all types.
* cranelift: Restrict `bint` to scalar values only
In #4104 we discussed whether it makes sense for the division and
remainder ops to support vector types. We concluded that because most
hardware doesn't support it directly, it probably is not ideal to force
all backends to polyfill it. In the future we can always reverse this
decision, perhaps with a platform-independent legalization.
This PR restricts the allowed types on the CLIF ops to integer types
only.
Currently, we have partial Spectre mitigation: we protect heap accesses
with dynamic bounds checks. Specifically, we guard against errant
accesses on the misspeculated path beyond the bounds-check conditional
branch by adding a conditional move that is also dependent on the
bounds-check condition. This data dependency on the condition is not
speculated and thus will always pick the "safe" value (in the heap case,
a NULL address) on the misspeculated path, until the pipeline flushes
and recovers onto the correct path.
This PR uses the same technique both for table accesses -- used to
implement Wasm tables -- and for jumptables, used to implement Wasm
`br_table` instructions.
In the case of Wasm tables, the cmove picks the table base address on
the misspeculated path. This is equivalent to reading the first table
entry. This prevents loads of arbitrary data addresses on the
misspeculated path.
In the case of `br_table`, the cmove picks index 0 on the misspeculated
path. This is safer than allowing a branch to an address loaded from an
index under misspeculation (i.e., it preserves control-flow integrity
even under misspeculation).
The table mitigation is controlled by a Cranelift setting, on by
default. The br_table mitigation is always on, because it is part of the
single lowering pseudoinstruction. In both cases, the impact should be
minimal: a single extra cmove in a (relatively) rarely-used operation.
The table mitigation is architecture-independent (happens during
legalization); the br_table mitigation has been implemented for both x64
and aarch64. (I don't know enough about s390x to implement this
confidently there, but would happily review a PR to do the same on that
platform.)
With these fixes, all this PR has to do is instantiate and run the
checker on the `regalloc2::Output`. This is off by default, and is
enabled by setting the `regalloc_checker` Cranelift option.
This restores the old functionality provided by e.g. the
`backtracking_checked` regalloc algorithm setting rather than
`backtracking` when we were still on regalloc.rs.
This PR switches Cranelift over to the new register allocator, regalloc2.
See [this document](https://gist.github.com/cfallin/08553421a91f150254fe878f67301801)
for a summary of the design changes. This switchover has implications for
core VCode/MachInst types and the lowering pass.
Overall, this change brings improvements to both compile time and speed of
generated code (runtime), as reported in #3942:
```
Benchmark Compilation (wallclock) Execution (wallclock)
blake3-scalar 25% faster 28% faster
blake3-simd no diff no diff
meshoptimizer 19% faster 17% faster
pulldown-cmark 17% faster no diff
bz2 15% faster no diff
SpiderMonkey, 21% faster 2% faster
fib(30)
clang.wasm 42% faster N/A
```
This change removes all variants of `load*_complex` and `store*_complex`
from Cranelift; this is a breaking change to the instructions exposed by
CLIF. The complete list of instructions removed is: `load_complex`,
`store_complex`, `uload8_complex`, `sload8_complex`, `istore8_complex`,
`sload8_complex`, `uload16_complex`, `sload16_complex`,
`istore16_complex`, `uload32_complex`, `sload32_complex`,
`istore32_complex`, `uload8x8_complex`, `sload8x8_complex`,
`sload16x4_complex`, `uload16x4_complex`, `uload32x2_complex`,
`sload32x2_complex`.
The rationale for this removal is that the Cranelift backend now has the
ability to pattern-match multiple upstream additions in order to
calculate the address to access. Previously, this was not possible so
the `*_complex` instructions were needed. Over time, these instructions
have fallen out of use in this repository, making the additional
overhead of maintaining them a chore.
Looking at [the `fcmp`
documentation](https://docs.rs/cranelift-codegen/0.80.0/cranelift_codegen/ir/trait.InstBuilder.html#method.fcmp)--generated
from Cranelift's instruction definitions, the charts explaining the
logic for the various conditions is unreadable. Since rendering those charts
as plain text is problematic, this change wraps them as code sections
for a consistent layout.
This opcode was removed as part of the old-backend cleanup in #3446.
While this opcode will definitely go away eventually, it is
unfortunately still used today in Lucet (as we just discovered while
working to upgrade Lucet's pinned Cranelift version). Lucet is
deprecated and slated to eventually be completely sunset in favor of
Wasmtime; but until that happens, we need to keep this opcode.
This also paves the way for unifying TargetIsa and MachBackend, since now they map one to one. In theory the two traits could be merged, which would be nice to limit the number of total concepts. Also they have quite different responsibilities, so it might be fine to keep them separate.
Interestingly, this PR started as removing RegInfo from the TargetIsa trait since the adapter returned a dummy value there. From the fallout, noticed that all Display implementations didn't needed an ISA anymore (since these were only used to render ISA specific registers). Also the whole family of RegInfo / ValueLoc / RegUnit was exclusively used for the old backend, and these could be removed. Notably, some IR instructions needed to be removed, because they were using RegUnit too: this was the oddball of regfill / regmove / regspill / copy_special, which were IR instructions inserted by the old regalloc. Fare thee well!
Implemented `Smulhi` for the Cranelift interpreter, performing signed
integer multiplication and producing the high half of a double-length
result.
Copyright (c) 2021, Arm Limited
Implemented the following Opcodes for the Cranelift interpreter:
- `Unarrow` to combine two SIMD vectors into a new vector with twice
the lanes but half the width, with signed inputs which are clamped to
`0x00`.
- `Uunarrow` to perform the same operation as `Unarrow` but treating
inputs as unsigned.
- `Snarrow` to perform the same operation as `Unarrow` but treating
both inputs and outputs as signed, and saturating accordingly.
Note that all 3 instructions saturate at the type boundaries.
Copyright (c) 2021, Arm Limited
- Fixed CI tests for AArch64 and old x86.
- Rename `simd-umulhi.clif` to `umulhi.clif`.
- Rename `simd-umulhi-aarch64.clif` to `simd-umulhi.clif`.
Copyright (c) 2021, Arm Limited.
The tests for the SIMD floating-point maximum and minimum operations
require particular care because the handling of the NaN values is
non-deterministic and may vary between platforms. There is no way to
match several NaN values in a test, so the solution is to extract the
non-deterministic test cases into a separate file that is subsequently
replicated for every backend under test, with adjustments made to the
expected results.
Copyright (c) 2021, Arm Limited.
Also, reorganize the AArch64-specific VCode instructions for unary
narrowing and widening vector operations, so that they are more
straightforward to use.
Copyright (c) 2021, Arm Limited.
