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| 1 | +module transformer |
| 2 | + |
| 3 | +struct KeyVal { |
| 4 | + key string |
| 5 | + value int |
| 6 | +} |
| 7 | + |
| 8 | +[if debug_bounds_checking ?] |
| 9 | +fn debug_bounds_checking(str string) { |
| 10 | + println(str) |
| 11 | +} |
| 12 | + |
| 13 | +// IndexState is used to track the index analysis performed when parsing the code |
| 14 | +// `IndexExpr` nodes are annotated with `is_direct`, indicating that the array index can be safely directly accessed. |
| 15 | + |
| 16 | +// The c_gen code check will handle this annotation and perform this direct memory access. The following cases are considered valid for this optimisation: |
| 17 | +// 1. the array size is known and has a `len` larger than the index requested |
| 18 | +// 2. the array was previously accessed with a higher value which would have reported the issue already |
| 19 | +// 3. the array was created from a range expression a := range[10..13] and the offset'ed indexes are safe |
| 20 | + |
| 21 | +// Current limitations: |
| 22 | +// * 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 |
| 23 | +// * `enum` and `const` indexes are not optimised (they could probably be looked up) |
| 24 | +// * for loops with multiple var in their init and/or inc are not analysed |
| 25 | +// * mut array are not analysed as their size can be reduced, but self-assignment in a single line |
| 26 | + |
| 27 | +pub struct IndexState { |
| 28 | +mut: |
| 29 | + // max_index has the biggest array index accessed for then named array |
| 30 | + // so if a[2] was set or read, it will be 2 |
| 31 | + // A new array with no .len will recorded as -1 (accessing a[0] would be invalid) |
| 32 | + // the value -2 is used to indicate that the array should not be analysed |
| 33 | + // this is used for a mut array |
| 34 | + max_index map[string]int |
| 35 | + // We need to snapshot when entering `if` and `for` blocks and restore on exit |
| 36 | + // as the statements may not be run. This is managed by indent() & unindent(). |
| 37 | + saved_disabled []bool |
| 38 | + saved_key_vals [][]KeyVal |
| 39 | +pub mut: |
| 40 | + // on encountering goto/break/continue statements we stop any analysis |
| 41 | + // for the current function (as the code is not linear anymore) |
| 42 | + disabled bool |
| 43 | + level int |
| 44 | +} |
| 45 | + |
| 46 | +// we are remembering the last array accessed and checking if the value is safe |
| 47 | +// the node is updated with this information which can then be used by the code generators |
| 48 | +fn (mut i IndexState) safe_access(key string, new int) bool { |
| 49 | + $if no_bounds_checking { |
| 50 | + return false |
| 51 | + } |
| 52 | + if i.disabled { |
| 53 | + return false |
| 54 | + } |
| 55 | + old := i.max_index[key] or { |
| 56 | + debug_bounds_checking('$i.level ${key}.len = $new') |
| 57 | + i.max_index[key] = new |
| 58 | + return false |
| 59 | + } |
| 60 | + if new > old { |
| 61 | + if old < -1 { |
| 62 | + debug_bounds_checking('$i.level $key[$new] unsafe (mut array)') |
| 63 | + return false |
| 64 | + } |
| 65 | + debug_bounds_checking('$i.level $key[$new] unsafe (index was $old)') |
| 66 | + i.max_index[key] = new |
| 67 | + return false |
| 68 | + } |
| 69 | + debug_bounds_checking('$i.level $key[$new] safe (index is $old)') |
| 70 | + return true |
| 71 | +} |
| 72 | + |
| 73 | +// safe_offset returns for a previvous array what was the highest |
| 74 | +// offset we ever accessed for that identifier |
| 75 | +fn (mut i IndexState) safe_offset(key string) int { |
| 76 | + $if no_bounds_checking { |
| 77 | + return -2 |
| 78 | + } |
| 79 | + if i.disabled { |
| 80 | + return -2 |
| 81 | + } |
| 82 | + return i.max_index[key] or { -1 } |
| 83 | +} |
| 84 | + |
| 85 | +// indent is used for when encountering new code blocks (if, for and functions) |
| 86 | +// The code analysis needs to take into consideration blocks of code which |
| 87 | +// may not run at runtime (if/for) and therefore even if a new maximum for an |
| 88 | +// index access is found on an if branch it can not be used within the parent |
| 89 | +// code. The same is true with for blocks. indent() snapshot the current state, |
| 90 | +// to allow restoration with unindent() |
| 91 | +// Also within a function, analysis must be `disabled` when goto or break are |
| 92 | +// encountered as the code flow is then not lineear, and only restart when a |
| 93 | +// new function analysis is started. |
| 94 | +[if !no_bounds_checking] |
| 95 | +fn (mut i IndexState) indent(is_function bool) { |
| 96 | + mut kvs := []KeyVal{cap: i.max_index.len} |
| 97 | + for k, v in i.max_index { |
| 98 | + kvs << KeyVal{k, v} |
| 99 | + } |
| 100 | + i.saved_disabled << i.disabled |
| 101 | + i.saved_key_vals << kvs |
| 102 | + if is_function { |
| 103 | + i.disabled = false |
| 104 | + } |
| 105 | + i.level += 1 |
| 106 | +} |
| 107 | + |
| 108 | +// restoring the data as it was before the if/for/unsafe block |
| 109 | +[if !no_bounds_checking] |
| 110 | +fn (mut i IndexState) unindent() { |
| 111 | + i.level -= 1 |
| 112 | + mut keys := []string{cap: i.max_index.len} |
| 113 | + for k, _ in i.max_index { |
| 114 | + keys << k |
| 115 | + } |
| 116 | + for k in keys { |
| 117 | + i.max_index.delete(k) |
| 118 | + } |
| 119 | + for saved in i.saved_key_vals.pop() { |
| 120 | + i.max_index[saved.key] = saved.value |
| 121 | + } |
| 122 | + i.disabled = i.saved_disabled.pop() |
| 123 | +} |
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