A dynamic heap address computation may create up to two conditional
branches: the usual bounds-check, but also (in some cases) an
offset-addition overflow check.
The x64 backend had reversed the condition code for this check,
resulting in an always-trapping execution for a valid offset. I'm
somewhat surprised this has existed so long, but I suppose the
particular conditions (large offset, small offset guard, dynamic heap)
have been somewhat rare in our testing so far.
Found via fuzzing in #2453.
* Make cranelift_codegen::isa::unwind::input public
* Move UnwindCode's common offset field out of the structure
* Make MachCompileResult::unwind_info more generic
* Record initial stack pointer offset
A new associated type Info is added to MachInstEmit, which is the
immutable counterpart to State. It can't easily be constructed from an
ABICallee, since it would require adding an associated type to the
latter, and making so leaks the associated type in a lot of places in
the code base and makes the code harder to read. Instead, the EmitInfo
state can simply be passed to the `Vcode::emit` function directly.
This PR updates the AArch64 ABI implementation so that it (i) properly
respects that v8-v15 inclusive have callee-save lower halves, and
caller-save upper halves, by conservatively approximating (to full
registers) in the appropriate directions when generating prologue
caller-saves and when informing the regalloc of clobbered regs across
callsites.
In order to prevent saving all of these vector registers in the prologue
of every non-leaf function due to the above approximation, this also
makes use of a new regalloc.rs feature to exclude call instructions'
writes from the clobber set returned by register allocation. This is
safe whenever the caller and callee have the same ABI (because anything
the callee could clobber, the caller is allowed to clobber as well
without saving it in the prologue).
Fixes#2254.
Previously, in #2128, we factored out a common "vanilla 64-bit ABI"
implementation from the AArch64 ABI code, with the idea that this should
be largely compatible with x64. This PR alters the new x64 backend to
make use of the shared infrastructure, removing the duplication that
existed previously. The generated code is nearly (not exactly) the same;
the only difference relates to how the clobber-save region is padded in
the prologue.
This also changes some register allocations in the aarch64 code because
call support in the shared ABI infra now passes a temp vreg in, rather
than requiring use of a fixed, non-allocable temp; tests have been
updated, and the runtime behavior is unchanged.
This change is a pure refactoring--no change to functionality. It removes newlines between the `use ...` statements in the x64 backend so that rustfmt can format them according to its convention. I noticed some files had followed a manual convention but subsequent additions did not seem to fit; this change fixes that and lightly coalesces some of the occurrences of `use a::b; use a::c;` into `use::{b, c}`.
Before this patch, running the x64 new backend would require both
compiling with --features experimental_x64 and running with
`use_new_backend`.
This patches changes this behavior so that the runtime flag is not
needed anymore: using the feature flag will enforce usage of the new
backend everywhere, making using and testing it much simpler:
cargo run --features experimental_x64 ;; other CLI options/flags
This also gives a hint at what the meta language generation would look
like after switching to the new backend.
Compiling only with the x64 codegen flag gives a nice compile time speedup.
- Properly mask constant values down to appropriate width when
generating a constant value directly in aarch64 backend. This was a
miscompilation introduced in the new-isel refactor. In combination
with failure to respect NarrowValueMode, this resulted in a very
subtle bug when an `i32` constant was used in bit-twiddling logic.
- Add support for `iadd_ifcout` in aarch64 backend as used in explicit
heap-check mode. With this change, we no longer fail heap-related
tests with the huge-heap-region mode disabled.
- Remove a panic that was occurring in some tests that are currently
ignored on aarch64, by simply returning empty/default information in
`value_label` functionality rather than touching unimplemented APIs.
This is not a bugfix per-se, but removes confusing panic messages from
`cargo test` output that might otherwise mislead.
compilation.
This saves ~0.14% instruction count, ~0.18% allocated bytes, and ~1.5%
allocated blocks on a `clif-util wasm` compilation of `bz2.wasm` for
aarch64.
