codegen/src/context.rs

//! Cranelift compilation context and main entry point.
//!
//! When compiling many small functions, it is important to avoid repeatedly allocating and
//! deallocating the data structures needed for compilation. The `Context` struct is used to hold
//! on to memory allocations between function compilations.
//!
//! The context does not hold a `TargetIsa` instance which has to be provided as an argument
//! instead. This is because an ISA instance is immutable and can be used by multiple compilation
//! contexts concurrently. Typically, you would have one context per compilation thread and only a
//! single ISA instance.

use crate::alias_analysis::AliasAnalysis;
use crate::dce::do_dce;
use crate::dominator_tree::DominatorTree;
use crate::flowgraph::ControlFlowGraph;
use crate::ir::Function;
use crate::isa::TargetIsa;
use crate::legalizer::simple_legalize;
use crate::licm::do_licm;
use crate::loop_analysis::LoopAnalysis;
use crate::machinst::CompiledCode;
use crate::nan_canonicalization::do_nan_canonicalization;
use crate::remove_constant_phis::do_remove_constant_phis;
use crate::result::{CodegenResult, CompileResult};
use crate::settings::{FlagsOrIsa, OptLevel};
use crate::simple_gvn::do_simple_gvn;
use crate::simple_preopt::do_preopt;
use crate::unreachable_code::eliminate_unreachable_code;
use crate::verifier::{verify_context, VerifierErrors, VerifierResult};
use crate::{timing, CompileError};
#[cfg(feature = "souper-harvest")]
use alloc::string::String;
use alloc::vec::Vec;

#[cfg(feature = "souper-harvest")]
use crate::souper_harvest::do_souper_harvest;

/// Persistent data structures and compilation pipeline.
pub struct Context {
    /// The function we're compiling.
    pub func: Function,

    /// The control flow graph of `func`.
    pub cfg: ControlFlowGraph,

    /// Dominator tree for `func`.
    pub domtree: DominatorTree,

    /// Loop analysis of `func`.
    pub loop_analysis: LoopAnalysis,

    /// Result of MachBackend compilation, if computed.
    compiled_code: Option<CompiledCode>,

    /// Flag: do we want a disassembly with the CompiledCode?
    pub want_disasm: bool,
}

impl Context {
    /// Allocate a new compilation context.
    ///
    /// The returned instance should be reused for compiling multiple functions in order to avoid
    /// needless allocator thrashing.
    pub fn new() -> Self {
        Self::for_function(Function::new())
    }

    /// Allocate a new compilation context with an existing Function.
    ///
    /// The returned instance should be reused for compiling multiple functions in order to avoid
    /// needless allocator thrashing.
    pub fn for_function(func: Function) -> Self {
        Self {
            func,
            cfg: ControlFlowGraph::new(),
            domtree: DominatorTree::new(),
            loop_analysis: LoopAnalysis::new(),
            compiled_code: None,
            want_disasm: false,
        }
    }

    /// Clear all data structures in this context.
    pub fn clear(&mut self) {
        self.func.clear();
        self.cfg.clear();
        self.domtree.clear();
        self.loop_analysis.clear();
        self.compiled_code = None;
        self.want_disasm = false;
    }

    /// Returns the compilation result for this function, available after any `compile` function
    /// has been called.
    pub fn compiled_code(&self) -> Option<&CompiledCode> {
        self.compiled_code.as_ref()
    }

    /// Set the flag to request a disassembly when compiling with a
    /// `MachBackend` backend.
    pub fn set_disasm(&mut self, val: bool) {
        self.want_disasm = val;
    }

    /// Compile the function, and emit machine code into a `Vec<u8>`.
    ///
    /// Run the function through all the passes necessary to generate code for the target ISA
    /// represented by `isa`, as well as the final step of emitting machine code into a
    /// `Vec<u8>`. The machine code is not relocated. Instead, any relocations can be obtained
    /// from `compiled_code()`.
    ///
    /// This function calls `compile` and `emit_to_memory`, taking care to resize `mem` as
    /// needed, so it provides a safe interface.
    ///
    /// Returns information about the function's code and read-only data.
    pub fn compile_and_emit(
        &mut self,
        isa: &dyn TargetIsa,
        mem: &mut Vec<u8>,
    ) -> CompileResult<&CompiledCode> {
        let compiled_code = self.compile(isa)?;
        let code_info = compiled_code.code_info();
        let old_len = mem.len();
        mem.resize(old_len + code_info.total_size as usize, 0);
        mem[old_len..].copy_from_slice(compiled_code.code_buffer());
        Ok(compiled_code)
    }

    /// Compile the function.
    ///
    /// Run the function through all the passes necessary to generate code for the target ISA
    /// represented by `isa`. This does not include the final step of emitting machine code into a
    /// code sink.
    ///
    /// Returns information about the function's code and read-only data.
    pub fn compile(&mut self, isa: &dyn TargetIsa) -> CompileResult<&CompiledCode> {
        let _tt = timing::compile();

        let mut inner = || {
            self.verify_if(isa)?;

            let opt_level = isa.flags().opt_level();
            log::trace!(
                "Compiling (opt level {:?}):\n{}",
                opt_level,
                self.func.display()
            );

            self.compute_cfg();
            if opt_level != OptLevel::None {
                self.preopt(isa)?;
            }
            if isa.flags().enable_nan_canonicalization() {
                self.canonicalize_nans(isa)?;
            }

            self.legalize(isa)?;
            if opt_level != OptLevel::None {
                self.compute_domtree();
                self.compute_loop_analysis();
                self.licm(isa)?;
                self.simple_gvn(isa)?;
            }

            self.compute_domtree();
            self.eliminate_unreachable_code(isa)?;
            if opt_level != OptLevel::None {
                self.dce(isa)?;
            }

            self.remove_constant_phis(isa)?;

            if opt_level != OptLevel::None && isa.flags().enable_alias_analysis() {
                self.replace_redundant_loads()?;
                self.simple_gvn(isa)?;
            }

            let result = isa.compile_function(&self.func, self.want_disasm)?;
            self.compiled_code = Some(result);
            Ok(())
        };

        inner()
            .map(|_| self.compiled_code.as_ref().unwrap())
            .map_err(|error| CompileError {
                inner: error,
                func: &self.func,
            })
    }

    /// If available, return information about the code layout in the
    /// final machine code: the offsets (in bytes) of each basic-block
    /// start, and all basic-block edges.
    pub fn get_code_bb_layout(&self) -> Option<(Vec<usize>, Vec<(usize, usize)>)> {
        if let Some(result) = self.compiled_code.as_ref() {
            Some((
                result.bb_starts.iter().map(|&off| off as usize).collect(),
                result
                    .bb_edges
                    .iter()
                    .map(|&(from, to)| (from as usize, to as usize))
                    .collect(),
            ))
        } else {
            None
        }
    }

    /// Creates unwind information for the function.
    ///
    /// Returns `None` if the function has no unwind information.
    #[cfg(feature = "unwind")]
    pub fn create_unwind_info(
        &self,
        isa: &dyn TargetIsa,
    ) -> CodegenResult<Option<crate::isa::unwind::UnwindInfo>> {
        let unwind_info_kind = isa.unwind_info_kind();
        let result = self.compiled_code.as_ref().unwrap();
        isa.emit_unwind_info(result, unwind_info_kind)
    }

    /// Run the verifier on the function.
    ///
    /// Also check that the dominator tree and control flow graph are consistent with the function.
    pub fn verify<'a, FOI: Into<FlagsOrIsa<'a>>>(&self, fisa: FOI) -> VerifierResult<()> {
        let mut errors = VerifierErrors::default();
        let _ = verify_context(&self.func, &self.cfg, &self.domtree, fisa, &mut errors);

        if errors.is_empty() {
            Ok(())
        } else {
            Err(errors)
        }
    }

    /// Run the verifier only if the `enable_verifier` setting is true.
    pub fn verify_if<'a, FOI: Into<FlagsOrIsa<'a>>>(&self, fisa: FOI) -> CodegenResult<()> {
        let fisa = fisa.into();
        if fisa.flags.enable_verifier() {
            self.verify(fisa)?;
        }
        Ok(())
    }

    /// Perform dead-code elimination on the function.
    pub fn dce<'a, FOI: Into<FlagsOrIsa<'a>>>(&mut self, fisa: FOI) -> CodegenResult<()> {
        do_dce(&mut self.func, &mut self.domtree);
        self.verify_if(fisa)?;
        Ok(())
    }

    /// Perform constant-phi removal on the function.
    pub fn remove_constant_phis<'a, FOI: Into<FlagsOrIsa<'a>>>(
        &mut self,
        fisa: FOI,
    ) -> CodegenResult<()> {
        do_remove_constant_phis(&mut self.func, &mut self.domtree);
        self.verify_if(fisa)?;
        Ok(())
    }

    /// Perform pre-legalization rewrites on the function.
    pub fn preopt(&mut self, isa: &dyn TargetIsa) -> CodegenResult<()> {
        do_preopt(&mut self.func, &mut self.cfg, isa);
        self.verify_if(isa)?;
        Ok(())
    }

    /// Perform NaN canonicalizing rewrites on the function.
    pub fn canonicalize_nans(&mut self, isa: &dyn TargetIsa) -> CodegenResult<()> {
        do_nan_canonicalization(&mut self.func);
        self.verify_if(isa)
    }

    /// Run the legalizer for `isa` on the function.
    pub fn legalize(&mut self, isa: &dyn TargetIsa) -> CodegenResult<()> {
        // Legalization invalidates the domtree and loop_analysis by mutating the CFG.
        // TODO: Avoid doing this when legalization doesn't actually mutate the CFG.
        self.domtree.clear();
        self.loop_analysis.clear();

        // Run some specific legalizations only.
        simple_legalize(&mut self.func, &mut self.cfg, isa);
        self.verify_if(isa)
    }

    /// Compute the control flow graph.
    pub fn compute_cfg(&mut self) {
        self.cfg.compute(&self.func)
    }

    /// Compute dominator tree.
    pub fn compute_domtree(&mut self) {
        self.domtree.compute(&self.func, &self.cfg)
    }

    /// Compute the loop analysis.
    pub fn compute_loop_analysis(&mut self) {
        self.loop_analysis
            .compute(&self.func, &self.cfg, &self.domtree)
    }

    /// Compute the control flow graph and dominator tree.
    pub fn flowgraph(&mut self) {
        self.compute_cfg();
        self.compute_domtree()
    }

    /// Perform simple GVN on the function.
    pub fn simple_gvn<'a, FOI: Into<FlagsOrIsa<'a>>>(&mut self, fisa: FOI) -> CodegenResult<()> {
        do_simple_gvn(&mut self.func, &mut self.domtree);
        self.verify_if(fisa)
    }

    /// Perform LICM on the function.
    pub fn licm(&mut self, isa: &dyn TargetIsa) -> CodegenResult<()> {
        do_licm(
            &mut self.func,
            &mut self.cfg,
            &mut self.domtree,
            &mut self.loop_analysis,
        );
        self.verify_if(isa)
    }

    /// Perform unreachable code elimination.
    pub fn eliminate_unreachable_code<'a, FOI>(&mut self, fisa: FOI) -> CodegenResult<()>
    where
        FOI: Into<FlagsOrIsa<'a>>,
    {
        eliminate_unreachable_code(&mut self.func, &mut self.cfg, &self.domtree);
        self.verify_if(fisa)
    }

    /// Replace all redundant loads with the known values in
    /// memory. These are loads whose values were already loaded by
    /// other loads earlier, as well as loads whose values were stored
    /// by a store instruction to the same instruction (so-called
    /// "store-to-load forwarding").
    pub fn replace_redundant_loads(&mut self) -> CodegenResult<()> {
        let mut analysis = AliasAnalysis::new(&mut self.func, &self.domtree);
        analysis.compute_and_update_aliases();
        Ok(())
    }

    /// Harvest candidate left-hand sides for superoptimization with Souper.
    #[cfg(feature = "souper-harvest")]
    pub fn souper_harvest(
        &mut self,
        out: &mut std::sync::mpsc::Sender<String>,
    ) -> CodegenResult<()> {
        do_souper_harvest(&self.func, out);
        Ok(())
    }
}