Method emit_prologue

winch/codegen/src/codegen/mod.rs:150–207

Code generation prologue.

(mut self)

    /// Code generation prologue.
    pub fn emit_prologue(mut self) -> Result<CodeGen<'a, 'translation, 'data, M, Emission>> {
        let vmctx = self
            .sig
            .params()
            .first()
            .ok_or_else(|| format_err!(CodeGenError::vmcontext_arg_expected()))?
            .unwrap_reg();

        self.masm.start_source_loc(Default::default())?;
        // We need to use the vmctx parameter before pinning it for stack checking.
        self.masm.prologue(vmctx)?;

        // Pin the `VMContext` pointer.
        self.masm.mov(
            writable!(vmctx!(M)),
            vmctx.into(),
            self.env.ptr_type().try_into()?,
        )?;

        self.masm.reserve_stack(self.context.frame.locals_size)?;
        self.spill_register_arguments()?;

        let defined_locals_range = &self.context.frame.defined_locals_range;
        self.masm.zero_mem_range(defined_locals_range.as_range())?;

        // Save the results base parameter register into its slot.

        if self.sig.params.has_retptr() {
            match self.sig.params.unwrap_results_area_operand() {
                ABIOperand::Reg { ty, reg, .. } => {
                    let results_base_slot = self.context.frame.results_base_slot.as_ref().unwrap();
                    ensure!(
                        results_base_slot.addressed_from_sp(),
                        CodeGenError::sp_addressing_expected(),
                    );
                    let addr = self.masm.local_address(results_base_slot)?;
                    self.masm.store((*reg).into(), addr, (*ty).try_into()?)?;
                }
                // The result base parameter is a stack parameter, addressed
                // from FP.
                _ => {}
            }
        }

        self.masm.end_source_loc()?;

        Ok(CodeGen {
            sig: self.sig,
            context: self.context.for_emission(),
            masm: self.masm,
            env: self.env,
            tunables: self.tunables,
            source_location: self.source_location,
            control_frames: self.control_frames,
            fuel_consumed: self.fuel_consumed,
            phase: PhantomData,
        })
    }