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| author | John Hodge <tpg@ucc.asn.au> | 2017-12-23 12:53:08 +0800 |
|---|---|---|
| committer | John Hodge <tpg@ucc.asn.au> | 2017-12-23 12:53:08 +0800 |
| commit | 0f628b66ef92f740e4fb41ff45956211f63eb421 (patch) | |
| tree | 2b496db49c6f2957d8a6c4cb56ed35c0eeae4f00 /Notes | |
| parent | c54c79b06fcbb369a9df82d2f526def0cb2b4474 (diff) | |
| download | mrust-0f628b66ef92f740e4fb41ff45956211f63eb421.tar.gz | |
Notes - More ideas for optimisations
Diffstat (limited to 'Notes')
| -rw-r--r-- | Notes/MIR-Optimisations.md | 16 |
1 files changed, 16 insertions, 0 deletions
diff --git a/Notes/MIR-Optimisations.md b/Notes/MIR-Optimisations.md index e83f7cd3..57f29c88 100644 --- a/Notes/MIR-Optimisations.md +++ b/Notes/MIR-Optimisations.md @@ -91,6 +91,18 @@ fn do_replacements(stmt) ``` +Reverse De-temporary +==================== + +Allows removing useless temporaries (e.g. function returns) + +IDEA ONLY. +- Find `... = Local(n)` +- Find where it was defined +- If the destination was invalidated in that time, don't do anything +- If it's mutated or otherwise accessed in the intervening time, don't do anything with it +- If the value is Copy and it's used elsewhere, don't do anything +- Otherwise, remove the assignment and move upwards Return Backprop =============== @@ -119,6 +131,10 @@ Remove assignments where the assigned value isn't read/borrowed before next assi Algorithm --------- +- For all assignments of the form `Local(n) = ...`, seek forwards until the next use or loopback +- If the next use of that particular lvalue is an assignment, delete the original assignment +- If the lvalue is fully reassigned, delete the original assignment + - Fully reassignment means that the LHS of Index/Field is mutated Pseudocode --------- |