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transformer: refactor + apply transform to (hopefully) all nodes (#13216
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,123 @@ | ||
| module transformer | ||
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| struct KeyVal { | ||
| key string | ||
| value int | ||
| } | ||
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| [if debug_bounds_checking ?] | ||
| fn debug_bounds_checking(str string) { | ||
| println(str) | ||
| } | ||
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| // IndexState is used to track the index analysis performed when parsing the code | ||
| // `IndexExpr` nodes are annotated with `is_direct`, indicating that the array index can be safely directly accessed. | ||
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| // The c_gen code check will handle this annotation and perform this direct memory access. The following cases are considered valid for this optimisation: | ||
| // 1. the array size is known and has a `len` larger than the index requested | ||
| // 2. the array was previously accessed with a higher value which would have reported the issue already | ||
| // 3. the array was created from a range expression a := range[10..13] and the offset'ed indexes are safe | ||
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| // Current limitations: | ||
| // * any function using break/continue or goto/label stopped from being optimised as soon as the relevant AST nodes are found as the code can not be ensured to be sequential | ||
| // * `enum` and `const` indexes are not optimised (they could probably be looked up) | ||
| // * for loops with multiple var in their init and/or inc are not analysed | ||
| // * mut array are not analysed as their size can be reduced, but self-assignment in a single line | ||
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| pub struct IndexState { | ||
| mut: | ||
| // max_index has the biggest array index accessed for then named array | ||
| // so if a[2] was set or read, it will be 2 | ||
| // A new array with no .len will recorded as -1 (accessing a[0] would be invalid) | ||
| // the value -2 is used to indicate that the array should not be analysed | ||
| // this is used for a mut array | ||
| max_index map[string]int | ||
| // We need to snapshot when entering `if` and `for` blocks and restore on exit | ||
| // as the statements may not be run. This is managed by indent() & unindent(). | ||
| saved_disabled []bool | ||
| saved_key_vals [][]KeyVal | ||
| pub mut: | ||
| // on encountering goto/break/continue statements we stop any analysis | ||
| // for the current function (as the code is not linear anymore) | ||
| disabled bool | ||
| level int | ||
| } | ||
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| // we are remembering the last array accessed and checking if the value is safe | ||
| // the node is updated with this information which can then be used by the code generators | ||
| fn (mut i IndexState) safe_access(key string, new int) bool { | ||
| $if no_bounds_checking { | ||
| return false | ||
| } | ||
| if i.disabled { | ||
| return false | ||
| } | ||
| old := i.max_index[key] or { | ||
| debug_bounds_checking('$i.level ${key}.len = $new') | ||
| i.max_index[key] = new | ||
| return false | ||
| } | ||
| if new > old { | ||
| if old < -1 { | ||
| debug_bounds_checking('$i.level $key[$new] unsafe (mut array)') | ||
| return false | ||
| } | ||
| debug_bounds_checking('$i.level $key[$new] unsafe (index was $old)') | ||
| i.max_index[key] = new | ||
| return false | ||
| } | ||
| debug_bounds_checking('$i.level $key[$new] safe (index is $old)') | ||
| return true | ||
| } | ||
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| // safe_offset returns for a previvous array what was the highest | ||
| // offset we ever accessed for that identifier | ||
| fn (mut i IndexState) safe_offset(key string) int { | ||
| $if no_bounds_checking { | ||
| return -2 | ||
| } | ||
| if i.disabled { | ||
| return -2 | ||
| } | ||
| return i.max_index[key] or { -1 } | ||
| } | ||
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| // indent is used for when encountering new code blocks (if, for and functions) | ||
| // The code analysis needs to take into consideration blocks of code which | ||
| // may not run at runtime (if/for) and therefore even if a new maximum for an | ||
| // index access is found on an if branch it can not be used within the parent | ||
| // code. The same is true with for blocks. indent() snapshot the current state, | ||
| // to allow restoration with unindent() | ||
| // Also within a function, analysis must be `disabled` when goto or break are | ||
| // encountered as the code flow is then not lineear, and only restart when a | ||
| // new function analysis is started. | ||
| [if !no_bounds_checking] | ||
| fn (mut i IndexState) indent(is_function bool) { | ||
| mut kvs := []KeyVal{cap: i.max_index.len} | ||
| for k, v in i.max_index { | ||
| kvs << KeyVal{k, v} | ||
| } | ||
| i.saved_disabled << i.disabled | ||
| i.saved_key_vals << kvs | ||
| if is_function { | ||
| i.disabled = false | ||
| } | ||
| i.level += 1 | ||
| } | ||
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| // restoring the data as it was before the if/for/unsafe block | ||
| [if !no_bounds_checking] | ||
| fn (mut i IndexState) unindent() { | ||
| i.level -= 1 | ||
| mut keys := []string{cap: i.max_index.len} | ||
| for k, _ in i.max_index { | ||
| keys << k | ||
| } | ||
| for k in keys { | ||
| i.max_index.delete(k) | ||
| } | ||
| for saved in i.saved_key_vals.pop() { | ||
| i.max_index[saved.key] = saved.value | ||
| } | ||
| i.disabled = i.saved_disabled.pop() | ||
| } |
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