// fixFunctionReturns finds 'return' instructions and replaces them
// with appropriate `set pc, $__<name>_epilog` versions.
func fixFunctionReturns(ast *parser.AST, f *parser.Function) {
var instr *parser.Instruction
var expr *parser.Expression
var file, line, col int
var code []parser.Node
var ok bool
name := f.Children()[0].(*parser.Name)
exitLabel := "$__" + name.Data + "_epilog"
list := f.Children()[1:]
for i := range list {
if instr, ok = list[i].(*parser.Instruction); !ok {
continue
}
code = instr.Children()
name = code[0].(*parser.Name)
if name.Data != "return" {
continue
}
file, line, col = instr.File(), instr.Line(), instr.Col()
name.Data = "set"
code = append(code, nil, nil)
expr = parser.NewExpression(file, line, col)
expr.SetChildren([]parser.Node{
parser.NewName(file, line, col, "pc"),
})
code[1] = expr
expr = parser.NewExpression(file, line, col)
expr.SetChildren([]parser.Node{
parser.NewName(file, line, col, exitLabel),
})
code[2] = expr
instr.SetChildren(code)
}
}
// injectFunctionCode injects function prologs and epilogs.
func injectFunctionCode(ast *parser.AST, f *parser.Function) {
var tmp, code []parser.Node
var instr *parser.Instruction
var expr *parser.Expression
var idx int
name := f.Children()[0].(*parser.Name)
exitLabel := "$__" + name.Data + "_epilog"
file, line, col := name.File(), name.Line(), name.Col()
// Find list of referenced protected registers.
var regs []string
findProtectedRegisters(f.Children()[1:], ®s)
// Inject prolog and epilog code.
//
// For each protected register we found, we add appropriate
// stack push/pop instructions to preserve their state.
tmp = make([]parser.Node, len(f.Children())+(len(regs)*2)+2)
tmp[idx] = parser.NewLabel(file, line, col, name.Data)
idx++
// set push, $reg
for n := range regs {
instr = parser.NewInstruction(file, line, col)
code = make([]parser.Node, 3)
code[0] = parser.NewName(file, line, col, "set")
expr = parser.NewExpression(file, line, col)
expr.SetChildren([]parser.Node{
parser.NewName(file, line, col, "push"),
})
code[1] = expr
expr = parser.NewExpression(file, line, col)
expr.SetChildren([]parser.Node{
parser.NewName(file, line, col, regs[n]),
})
code[2] = expr
instr.SetChildren(code)
tmp[idx] = instr
idx++
}
// Regular code goes here.
copy(tmp[idx:], f.Children()[1:])
idx += len(f.Children()) - 1
// Label denoting the start of the epilog.
line, col = tmp[idx-1].Line()+1, 1
tmp[idx] = parser.NewLabel(file, line, col, exitLabel)
idx++
// set $reg, pop
for n := range regs {
instr = parser.NewInstruction(file, line, col)
code = make([]parser.Node, 3)
code[0] = parser.NewName(file, line, col, "set")
expr = parser.NewExpression(file, line, col)
expr.SetChildren([]parser.Node{
parser.NewName(file, line, col, regs[n]),
})
code[1] = expr
expr = parser.NewExpression(file, line, col)
expr.SetChildren([]parser.Node{
parser.NewName(file, line, col, "pop"),
})
code[2] = expr
instr.SetChildren(code)
tmp[idx] = instr
idx++
}
// set pc, pop
instr = parser.NewInstruction(file, line, col)
code = make([]parser.Node, 3)
code[0] = parser.NewName(file, line, col, "set")
expr = parser.NewExpression(file, line, col)
expr.SetChildren([]parser.Node{
parser.NewName(file, line, col, "pc"),
})
code[1] = expr
expr = parser.NewExpression(file, line, col)
expr.SetChildren([]parser.Node{
parser.NewName(file, line, col, "pop"),
})
code[2] = expr
instr.SetChildren(code)
tmp[idx] = instr
f.SetChildren(tmp)
}