1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129

//! Legalization of global values.
//!
//! This module exports the `expand_global_value` function which transforms a `global_value`
//! instruction into code that depends on the kind of global value referenced.

use crate::cursor::{Cursor, FuncCursor};
use crate::flowgraph::ControlFlowGraph;
use crate::ir::{self, InstBuilder};
use crate::isa::TargetIsa;

/// Expand a `global_value` instruction according to the definition of the global value.
pub fn expand_global_value(
    inst: ir::Inst,
    func: &mut ir::Function,
    _cfg: &mut ControlFlowGraph,
    isa: &dyn TargetIsa,
) {
    // Unpack the instruction.
    let gv = match func.dfg[inst] {
        ir::InstructionData::UnaryGlobalValue {
            opcode,
            global_value,
        } => {
            debug_assert_eq!(opcode, ir::Opcode::GlobalValue);
            global_value
        }
        _ => panic!("Wanted global_value: {}", func.dfg.display_inst(inst, None)),
    };

    match func.global_values[gv] {
        ir::GlobalValueData::VMContext => vmctx_addr(inst, func),
        ir::GlobalValueData::IAddImm {
            base,
            offset,
            global_type,
        } => iadd_imm_addr(inst, func, base, offset.into(), global_type),
        ir::GlobalValueData::Load {
            base,
            offset,
            global_type,
            readonly,
        } => load_addr(inst, func, base, offset, global_type, readonly, isa),
        ir::GlobalValueData::Symbol { .. } => symbol(inst, func, gv, isa),
    }
}

/// Expand a `global_value` instruction for a vmctx global.
fn vmctx_addr(inst: ir::Inst, func: &mut ir::Function) {
    // Get the value representing the `vmctx` argument.
    let vmctx = func
        .special_param(ir::ArgumentPurpose::VMContext)
        .expect("Missing vmctx parameter");

    // Replace the `global_value` instruction's value with an alias to the vmctx arg.
    let result = func.dfg.first_result(inst);
    func.dfg.clear_results(inst);
    func.dfg.change_to_alias(result, vmctx);
    func.layout.remove_inst(inst);
}

/// Expand a `global_value` instruction for an iadd_imm global.
fn iadd_imm_addr(
    inst: ir::Inst,
    func: &mut ir::Function,
    base: ir::GlobalValue,
    offset: i64,
    global_type: ir::Type,
) {
    let mut pos = FuncCursor::new(func).at_inst(inst);

    // Get the value for the lhs. For tidiness, expand VMContext here so that we avoid
    // `vmctx_addr` which creates an otherwise unneeded value alias.
    let lhs = if let ir::GlobalValueData::VMContext = pos.func.global_values[base] {
        pos.func
            .special_param(ir::ArgumentPurpose::VMContext)
            .expect("Missing vmctx parameter")
    } else {
        pos.ins().global_value(global_type, base)
    };

    // Simply replace the `global_value` instruction with an `iadd_imm`, reusing the result value.
    pos.func.dfg.replace(inst).iadd_imm(lhs, offset);
}

/// Expand a `global_value` instruction for a load global.
fn load_addr(
    inst: ir::Inst,
    func: &mut ir::Function,
    base: ir::GlobalValue,
    offset: ir::immediates::Offset32,
    global_type: ir::Type,
    readonly: bool,
    isa: &dyn TargetIsa,
) {
    // We need to load a pointer from the `base` global value, so insert a new `global_value`
    // instruction. This depends on the iterative legalization loop. Note that the IR verifier
    // detects any cycles in the `load` globals.
    let ptr_ty = isa.pointer_type();
    let mut pos = FuncCursor::new(func).at_inst(inst);
    pos.use_srcloc(inst);

    // Get the value for the base. For tidiness, expand VMContext here so that we avoid
    // `vmctx_addr` which creates an otherwise unneeded value alias.
    let base_addr = if let ir::GlobalValueData::VMContext = pos.func.global_values[base] {
        pos.func
            .special_param(ir::ArgumentPurpose::VMContext)
            .expect("Missing vmctx parameter")
    } else {
        pos.ins().global_value(ptr_ty, base)
    };

    // Global-value loads are always notrap and aligned. They may be readonly.
    let mut mflags = ir::MemFlags::trusted();
    if readonly {
        mflags.set_readonly();
    }

    // Perform the load.
    pos.func
        .dfg
        .replace(inst)
        .load(global_type, mflags, base_addr, offset);
}

/// Expand a `global_value` instruction for a symbolic name global.
fn symbol(inst: ir::Inst, func: &mut ir::Function, gv: ir::GlobalValue, isa: &dyn TargetIsa) {
    let ptr_ty = isa.pointer_type();
    func.dfg.replace(inst).symbol_value(ptr_ty, gv);
}