Struct Flags

pub struct Flags { /* private fields */ }

Expand description

Flags group shared.

Implementations§

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impl Flags

User-defined settings.

pub fn predicate_view(&self) -> PredicateView<'_>

Get a view of the boolean predicates.

pub fn regalloc_algorithm(&self) -> RegallocAlgorithm

Algorithm to use in register allocator.

Supported options:

backtracking: A backtracking allocator with range splitting; more expensive but generates better code.
single_pass: A single-pass algorithm that yields quick compilation but results in code with more register spills and moves.

pub fn opt_level(&self) -> OptLevel

Optimization level for generated code.

Supported levels:

none: Minimise compile time by disabling most optimizations.
speed: Generate the fastest possible code
speed_and_size: like “speed”, but also perform transformations aimed at reducing code size.

pub fn tls_model(&self) -> TlsModel

Defines the model used to perform TLS accesses.

pub fn stack_switch_model(&self) -> StackSwitchModel

Defines the model used to performing stack switching.

This determines the compilation of stack_switch instructions. If set to basic, we simply save all registers, update stack pointer and frame pointer (if needed), and jump to the target IP. If set to update_windows_tib, we additionally update information about the active stack in Windows’ Thread Information Block.

pub fn libcall_call_conv(&self) -> LibcallCallConv

Defines the calling convention to use for LibCalls call expansion.

This may be different from the ISA default calling convention.

The default value is to use the same calling convention as the ISA default calling convention.

This list should be kept in sync with the list of calling conventions available in isa/call_conv.rs.

pub fn probestack_size_log2(&self) -> u8

The log2 of the size of the stack guard region.

Stack frames larger than this size will have stack overflow checked by calling the probestack function.

The default is 12, which translates to a size of 4096.

pub fn probestack_strategy(&self) -> ProbestackStrategy

Controls what kinds of stack probes are emitted.

Supported strategies:

outline: Always emits stack probes as calls to a probe stack function.
inline: Always emits inline stack probes.

pub fn bb_padding_log2_minus_one(&self) -> u8

The log2 of the size to insert dummy padding between basic blocks

This is a debugging option for stressing various cases during code generation without requiring large functions. This will insert 0-byte padding between basic blocks of the specified size.

The amount of padding inserted two raised to the power of this value minus one. If this value is 0 then no padding is inserted.

The default for this option is 0 to insert no padding as it’s only intended for testing and development.

pub fn regalloc_checker(&self) -> bool

Enable the symbolic checker for register allocation.

This performs a verification that the register allocator preserves equivalent dataflow with respect to the original (pre-regalloc) program. This analysis is somewhat expensive. However, if it succeeds, it provides independent evidence (by a carefully-reviewed, from-first-principles analysis) that no regalloc bugs were triggered for the particular compilations performed. This is a valuable assurance to have as regalloc bugs can be very dangerous and difficult to debug.

pub fn regalloc_verbose_logs(&self) -> bool

Enable verbose debug logs for regalloc2.

This adds extra logging for regalloc2 output, that is quite valuable to understand decisions taken by the register allocator as well as debugging it. It is disabled by default, as it can cause many log calls which can slow down compilation by a large amount.

pub fn enable_alias_analysis(&self) -> bool

Do redundant-load optimizations with alias analysis.

This enables the use of a simple alias analysis to optimize away redundant loads. Only effective when opt_level is speed or speed_and_size.

pub fn enable_verifier(&self) -> bool

Run the Cranelift IR verifier at strategic times during compilation.

This makes compilation slower but catches many bugs. The verifier is always enabled by default, which is useful during development.

pub fn enable_pcc(&self) -> bool

Enable proof-carrying code translation validation.

This adds a proof-carrying-code mode. Proof-carrying code (PCC) is a strategy to verify that the compiler preserves certain properties or invariants in the compiled code. For example, a frontend that translates WebAssembly to CLIF can embed PCC facts in the CLIF, and Cranelift will verify that the final machine code satisfies the stated facts at each intermediate computed value. Loads and stores can be marked as “checked” and their memory effects can be verified as safe.

pub fn is_pic(&self) -> bool

Enable Position-Independent Code generation.

pub fn use_colocated_libcalls(&self) -> bool

Use colocated libcalls.

Generate code that assumes that libcalls can be declared “colocated”, meaning they will be defined along with the current function, such that they can use more efficient addressing.

pub fn enable_float(&self) -> bool

Enable the use of floating-point instructions.

Disabling use of floating-point instructions is not yet implemented.

pub fn enable_nan_canonicalization(&self) -> bool

Enable NaN canonicalization.

This replaces NaNs with a single canonical value, for users requiring entirely deterministic WebAssembly computation. This is not required by the WebAssembly spec, so it is not enabled by default.

pub fn enable_pinned_reg(&self) -> bool

Enable the use of the pinned register.

This register is excluded from register allocation, and is completely under the control of the end-user. It is possible to read it via the get_pinned_reg instruction, and to set it with the set_pinned_reg instruction.

pub fn enable_atomics(&self) -> bool

Enable the use of atomic instructions

pub fn enable_safepoints(&self) -> bool

Enable safepoint instruction insertions.

This will allow the emit_stack_maps() function to insert the safepoint instruction on top of calls and interrupt traps in order to display the live reference values at that point in the program.

pub fn enable_llvm_abi_extensions(&self) -> bool

Enable various ABI extensions defined by LLVM’s behavior.

In some cases, LLVM’s implementation of an ABI (calling convention) goes beyond a standard and supports additional argument types or behavior. This option instructs Cranelift codegen to follow LLVM’s behavior where applicable.

Currently, this applies only to Windows Fastcall on x86-64, and allows an i128 argument to be spread across two 64-bit integer registers. The Fastcall implementation otherwise does not support i128 arguments, and will panic if they are present and this option is not set.

pub fn enable_multi_ret_implicit_sret(&self) -> bool

Enable support for sret arg introduction when there are too many ret vals.

When there are more returns than available return registers, the return value has to be returned through the introduction of a return area pointer. Normally this return area pointer has to be introduced as ArgumentPurpose::StructReturn parameter, but for backward compatibility reasons Cranelift also supports implicitly introducing this parameter and writing the return values through it.

This option currently does not conform to platform ABIs and the used ABI should not be assumed to remain the same between Cranelift versions.

This option is deprecated and will be removed in the future.

Because of the above issues, and complexities of native ABI support for the concept in general, Cranelift’s support for multiple return values may also be removed in the future (#9510). For the most robust solution, it is recommended to build a convention on top of Cranelift’s primitives for passing multiple return values, for example by allocating a stackslot in the caller, passing it as an explicit StructReturn argument, storing return values in the callee, and loading results in the caller.

pub fn unwind_info(&self) -> bool

Generate unwind information.

This increases metadata size and compile time, but allows for the debugger to trace frames, is needed for GC tracing that relies on libunwind (such as in Wasmtime), and is unconditionally needed on certain platforms (such as Windows) that must always be able to unwind.

pub fn preserve_frame_pointers(&self) -> bool

Preserve frame pointers

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.

pub fn machine_code_cfg_info(&self) -> bool

Generate CFG metadata for machine code.

This increases metadata size and compile time, but allows for the embedder to more easily post-process or analyze the generated machine code. It provides code offsets for the start of each basic block in the generated machine code, and a list of CFG edges (with blocks identified by start offsets) between them. This is useful for, e.g., machine-code analyses that verify certain properties of the generated code.

pub fn enable_probestack(&self) -> bool

Enable the use of stack probes for supported calling conventions.

pub fn enable_jump_tables(&self) -> bool

Enable the use of jump tables in generated machine code.

pub fn enable_heap_access_spectre_mitigation(&self) -> bool

Enable Spectre mitigation on heap bounds checks.

This is a no-op for any heap that needs no bounds checks; e.g., if the limit is static and the guard region is large enough that the index cannot reach past it.

This option is enabled by default because it is highly recommended for secure sandboxing. The embedder should consider the security implications carefully before disabling this option.

pub fn enable_table_access_spectre_mitigation(&self) -> bool

Enable Spectre mitigation on table bounds checks.

This option uses a conditional move to ensure that when a table access index is bounds-checked and a conditional branch is used for the out-of-bounds case, a misspeculation of that conditional branch (falsely predicted in-bounds) will select an in-bounds index to load on the speculative path.

This option is enabled by default because it is highly recommended for secure sandboxing. The embedder should consider the security implications carefully before disabling this option.

pub fn enable_incremental_compilation_cache_checks(&self) -> bool

Enable additional checks for debugging the incremental compilation cache.

Enables additional checks that are useful during development of the incremental compilation cache. This should be mostly useful for Cranelift hackers, as well as for helping to debug false incremental cache positives for embedders.

This option is disabled by default and requires enabling the “incremental-cache” Cargo feature in cranelift-codegen.