This PR fixes two bugs in the riscv64 backend, where branch instructions were emitted in the middle of a basic block:
Constant emission, where the constants are inlined into the vcode and are jumped over at runtime,
The BrTableCheck pseudo-instruction, which was always emitted before a BrTable instruction, and would handle jumping to the default label.
The first bug was resolved by introducing two new psuedo instructions, LoadConst32 and LoadConst64. Both of these instructions serve to delay the original encoding to emission time, after regalloc2 has run.
The second bug was fixed by removing the BrTableCheck instruction. As it was always emitted directly before BrTable, it was easier to remove it and merge the two into a single instruction.
* Alias analysis: refactor for use by other driver loops.
This PR pulls the core of the alias analysis infrastructure into a
`process_inst()` method that operates on a single instruction, and
allows another compiler pass to apply store-to-load forwarding and
redundant-load elimination interleaved with other work. The existing
behavior remains unchanged; the pass's toplevel loop calls this
extracted method.
This refactor is a prerequisite for using the alias analysis as part of
a refactored egraph-based optimization framework.
* Review feedback: remove unneeded mut.
Rework the compilation of amodes in the aarch64 backend to stop reusing registers and instead generate fresh virtual registers for intermediates. This resolves some SSA checker violations with the aarch64 backend, and as a nice side-effect removes some unnecessary movs in the generated code.
As loading constants on aarch64 can take up to 4 instructions, we need to plumb through some additional registers. Rather than pass a fixed list of registers in, pass an allocation function.
Avoid reusing a destination virtual register for 64-bit constants in the s390x backend. This change addresses a case identified by the regalloc2 ssa validator, as the destination register was written to twice when constants were generated via the MachInst::gen_constant function.
Introduce a temporary for an intermediate value in the lowering of div in the x64 backend. Additionally, add a src argument to the shift_r smart constructor, which is why the diff got larger than just the div lowering.
Avoid reusing output registers in make_i64x2_from_lanes by threading the output name instead, and using smart constructors for x64_pinsrd instead of constructing the instructions directly.
* Cranelift: implement `heap_{load,store}` instruction legalization
This does not remove `heap_addr` yet, but it does factor out the common
bounds-check-and-compute-the-native-address functionality that is shared between
all of `heap_{addr,load,store}`.
Finally, this adds a missing optimization for when we can dedupe explicit bounds
checks for static memories and Spectre mitigations.
* Cranelift: Enable `heap_load_store_*` run tests on all targets
* Turn off probestack by default in Cranelift
The probestack feature is not implemented for the aarch64 and s390x
backends and currently the on-by-default status requires the aarch64 and
s390x implementations to be a stub. Turning off probestack by default
allows the s390x and aarch64 backends to panic with an error message to
avoid providing a false sense of security. When the probestack option is
implemented for all backends, however, it may be reasonable to
re-enable.
* aarch64: Improve codegen for AMode fallback
Currently the final fallback for finalizing an `AMode` will generate
both a constant-loading instruction as well as an `add` instruction to
the base register into the same temporary. This commit improves the
codegen by removing the `add` instruction and folding the final add into
the finalized `AMode`. This changes the `extendop` used but both
registers are 64-bit so shouldn't be affected by the extending
operation.
* aarch64: Implement inline stack probes
This commit implements inline stack probes for the aarch64 backend in
Cranelift. The support here is modeled after the x64 support where
unrolled probes are used up to a particular threshold after which a loop
is generated. The instructions here are similar in spirit to x64 except
that unlike x64 the stack pointer isn't modified during the unrolled
loop to avoid needing to re-adjust it back up at the end of the loop.
* Enable inline probestack for AArch64 and Riscv64
This commit enables inline probestacks for the AArch64 and Riscv64
architectures in the same manner that x86_64 has it enabled now. Some
more testing was additionally added since on Unix platforms we should be
guaranteed that Rust's stack overflow message is now printed too.
* Enable probestack for aarch64 in cranelift-fuzzgen
* Address review comments
* Remove implicit stack overflow traps from x64 backend
This commit removes implicit `StackOverflow` traps inserted by the x64
backend for stack-based operations. This was historically required when
stack overflow was detected with page faults but Wasmtime no longer
requires that since it's not suitable for wasm modules which call host
functions. Additionally no other backend implements this form of
implicit trap-code additions so this is intended to synchronize the
behavior of all the backends.
This fixes a test added prior for aarch64 to properly abort the process
instead of accidentally being caught by Wasmtime.
* Fix a style issue
* Cranelift: consider heap's guard pages when legalizing `heap_addr`
Fixes#5328
* Update comment to align more directly with implementation
* Add legalization tests for `heap_addr` and offset guard pages
Fix shadowing identified in #5322 for imul and swiden_high/swiden_low/uwiden_high/uwiden_low combinations in the x64 backend, and remove some redundant rules from the aarch64 dynamic neon ruleset. Additionally, add tests to the x64 backend showing that the imul specializations are firing.
Add assertions to the OperandCollector that show we're not using pinned vregs, and use reg_fixed_nonallocatable constraints when a real register is used with other constraint generation functions like reg_use etc.
* Cranelift: Define `heap_load` and `heap_store` instructions
* Cranelift: Implement interpreter support for `heap_load` and `heap_store`
* Cranelift: Add a suite runtests for `heap_{load,store}`
There are so many knobs we can twist for heaps and I wanted to exhaustively test
all of them, so I wrote a script to generate the tests. I've checked in the
script in case we want to make any changes in the future, but I don't think it
is worth adding this to CI to check that scripts are up to date or anything like
that.
* Review feedback
* Shrink the size of SigData in Cranelift
* Update cranelift/codegen/src/machinst/abi.rs
Co-authored-by: Jamey Sharp <jamey@minilop.net>
* Change ret arg length to u16
* Add test
Co-authored-by: Jamey Sharp <jamey@minilop.net>
Avoid naming %rcx as written by the CoffTlsGetAddr pseudo-instruction in the x64 backend, and instead emit a fixed-def constraint for a fresh VReg and %rcx.
Remove some unnecessary moves in the x64 gen_memcpy implementation -- the call instruction that's generated will already constrain the args to those registers.
We can encode more constants into 12-bit immediates if we do the following
rewrite for comparisons with odd constants:
A >= B + 1
==> A - 1 >= B
==> A > B
* Cranelift: Make `heap_addr` return calculated `base + index + offset`
Rather than return just the `base + index`.
(Note: I've chosen to use the nomenclature "index" for the dynamic operand and
"offset" for the static immediate.)
This move the addition of the `offset` into `heap_addr`, instead of leaving it
for the subsequent memory operation, so that we can Spectre-guard the full
address, and not allow speculative execution to read the first 4GiB of memory.
Before this commit, we were effectively doing
load(spectre_guard(base + index) + offset)
Now we are effectively doing
load(spectre_guard(base + index + offset))
Finally, this also corrects `heap_addr`'s documented semantics to say that it
returns an address that will trap on access if `index + offset + access_size` is
out of bounds for the given heap, rather than saying that the `heap_addr` itself
will trap. This matches the implemented behavior for static memories, and after
https://github.com/bytecodealliance/wasmtime/pull/5190 lands (which is blocked
on this commit) will also match the implemented behavior for dynamic memories.
* Update heap_addr docs
* Factor out `offset + size` to a helper
Modify return pseudo-instructions to have pairs of registers: virtual and real. This allows us to constrain the virtual registers to the real ones specified by the abi, instead of directly emitting moves to those real registers.
Remove the dependency on VCode for VReg allocation. This will simplify the changes in #5172, as that PR introduces the need to allocate temporary registers from the ABI context.
This change also allows us to remove some fields from VCode: reftyped_vregs_set and have_ref_values.
Add a MemFlags operand to the bitcast instruction, where only the
`big` and `little` flags are accepted. These define the lane order
to be used when casting between types of different lane counts.
Update all users to pass an appropriate MemFlags argument.
Implement lane swaps where necessary in the s390x back-end.
This is the final part necessary to fix
https://github.com/bytecodealliance/wasmtime/issues/4566.
Change add_nan_canon_seq to use vselect instead of bitselect.
This is more straightforward and removes bitcast operations.
Codegen should be unchanged.
The simplifier was performing an optimization to replace bitselect
with vselect if the all bytes of the condition mask could be shown
to be all ones or all zeros.
This optimization only ever made any difference in codegen on the
x64 target. Therefore, move this optimization to the x64 back-end
and perform it in ISLE instead. Resulting codegen should be
unchanged, with slightly improved compile time.
This also eliminates a few endian-dependent bitcast operations.
