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| -rw-r--r-- | libjulia/optimiser/README.md | 23 |
1 files changed, 21 insertions, 2 deletions
diff --git a/libjulia/optimiser/README.md b/libjulia/optimiser/README.md index 771cb707..24ee429c 100644 --- a/libjulia/optimiser/README.md +++ b/libjulia/optimiser/README.md @@ -54,8 +54,27 @@ As an example, neither ``mload`` nor ``mstore`` would be allowed. ## Full Function Inliner -## Variable Eliminator +## Rematerialisation + +The rematerialisation stage tries to replace variable references by the expression that +was last assigned to the variable. This is of course only beneficial if this expression +is comparatively cheap to evaluate. Furthermore, it is only semantically equivalent if +the value of the expression did not change between the point of assignment and the +point of use. The main benefit of this stage is that it can save stack slots if it +leads to a variable being eliminated completely (see below), but it can also +save a DUP opcode on the EVM if the expression is very cheap. + +The algorithm only allows movable expressions (see above for a definition) in this case. +Expressions that contain other variables are also disallowed if one of those variables +have been assigned to in the meantime. This is also not applied to variables where +assignment and use span across loops and conditionals. + +## Unused Definition Pruner + +If a variable or function is not referenced, it is removed from the code. +If there are two assignments to a variable where the first one is a movable expression +and the variable is not used between the two assignments (and the second is not inside +a loop or conditional, the first one is not inside), the first assignment is removed. -## Unused Declaration Pruner ## Function Unifier |