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//: Support jumps to special labels called 'targets'. Targets must be in the
//: same recipe as the jump, and must be unique in that recipe. Targets always
//: start with a '+'.
//:
//: We'll also treat 'break' and 'loop' as jumps. The choice of name is
//: just documentation about intent; use 'break' to indicate you're exiting
//: one or more loop nests, and 'loop' to indicate you're skipping to the next
//: iteration of some containing loop nest.
:(scenario jump_to_label)
recipe main [
jump +target:label
1:number <- copy 0
+target
]
-mem: storing 0 in location 1
:(before "End Mu Types Initialization")
put(Type_ordinal, "label", 0);
:(before "End Instruction Modifying Transforms")
Transform.push_back(transform_labels); // idempotent
:(code)
void transform_labels(const recipe_ordinal r) {
map<string, long long int> offset;
for (long long int i = 0; i < SIZE(get(Recipe, r).steps); ++i) {
const instruction& inst = get(Recipe, r).steps.at(i);
if (!inst.label.empty() && inst.label.at(0) == '+') {
if (!contains_key(offset, inst.label)) {
offset[inst.label] = i;
}
else {
raise_error << maybe(get(Recipe, r).name) << "duplicate label '" << inst.label << "'" << end();
// have all jumps skip some random but noticeable and deterministic amount of code
offset[inst.label] = 9999;
}
}
}
for (long long int i = 0; i < SIZE(get(Recipe, r).steps); ++i) {
instruction& inst = get(Recipe, r).steps.at(i);
if (inst.name == "jump") {
replace_offset(inst.ingredients.at(0), offset, i, r);
}
if (inst.name == "jump-if" || inst.name == "jump-unless") {
replace_offset(inst.ingredients.at(1), offset, i, r);
}
if ((inst.name == "loop" || inst.name == "break")
&& SIZE(inst.ingredients) == 1) {
replace_offset(inst.ingredients.at(0), offset, i, r);
}
if ((inst.name == "loop-if" || inst.name == "loop-unless"
|| inst.name == "break-if" || inst.name == "break-unless")
&& SIZE(inst.ingredients) == 2) {
replace_offset(inst.ingredients.at(1), offset, i, r);
}
}
}
:(code)
void replace_offset(reagent& x, /*const*/ map<string, long long int>& offset, const long long int current_offset, const recipe_ordinal r) {
if (!is_literal(x)) {
raise_error << maybe(get(Recipe, r).name) << "jump target must be offset or label but is " << x.original_string << '\n' << end();
x.set_value(0); // no jump by default
return;
}
if (x.initialized) return;
if (is_integer(x.name)) return; // non-labels will be handled like other number operands
if (!is_jump_target(x.name)) {
raise_error << maybe(get(Recipe, r).name) << "can't jump to label " << x.name << '\n' << end();
x.set_value(0); // no jump by default
return;
}
if (!contains_key(offset, x.name)) {
raise_error << maybe(get(Recipe, r).name) << "can't find label " << x.name << '\n' << end();
x.set_value(0); // no jump by default
return;
}
x.set_value(offset[x.name]-current_offset);
}
bool is_jump_target(string label) {
return label.at(0) == '+';
}
:(scenario break_to_label)
recipe main [
{
{
break +target:label
1:number <- copy 0
}
}
+target
]
-mem: storing 0 in location 1
:(scenario jump_if_to_label)
recipe main [
{
{
jump-if 1, +target:label
1:number <- copy 0
}
}
+target
]
-mem: storing 0 in location 1
:(scenario loop_unless_to_label)
recipe main [
{
{
loop-unless 0, +target:label # loop/break with a label don't care about braces
1:number <- copy 0
}
}
+target
]
-mem: storing 0 in location 1
:(scenario jump_runs_code_after_label)
recipe main [
# first a few lines of padding to exercise the offset computation
1:number <- copy 0
2:number <- copy 0
3:number <- copy 0
jump +target:label
4:number <- copy 0
+target
5:number <- copy 0
]
+mem: storing 0 in location 5
-mem: storing 0 in location 4
:(scenario recipe_fails_on_duplicate_jump_target)
% Hide_errors = true;
recipe main [
+label
1:number <- copy 0
+label
2:number <- copy 0
]
+error: main: duplicate label '+label'
:(scenario jump_ignores_nontarget_label)
% Hide_errors = true;
recipe main [
# first a few lines of padding to exercise the offset computation
1:number <- copy 0
2:number <- copy 0
3:number <- copy 0
jump $target:label
4:number <- copy 0
$target
5:number <- copy 0
]
+error: main: can't jump to label $target
|