mirror of
https://github.com/ethereum/solidity
synced 2023-10-03 13:03:40 +00:00
62 lines
2.5 KiB
Markdown
62 lines
2.5 KiB
Markdown
|
## IULIA Optimiser
|
||
|
|
|
||
|
|
The iulia optimiser consists of several stages and components that all transform
|
||
|
|
the AST in a semantically equivalent way. The goal is to end up either with code
|
||
|
|
that is shorter or at least only marginally longer but will allow further
|
||
|
|
optimisation steps.
|
||
|
|
|
||
|
|
The optimiser currently follows a purely greedy strategy and does not do any
|
||
|
|
backtracking.
|
||
|
|
|
||
|
|
## Disambiguator
|
||
|
|
|
||
|
|
The disambiguator takes an AST and returns a fresh copy where all identifiers have
|
||
|
|
names unique to the input AST. This is a prerequisite for all other optimiser stages.
|
||
|
|
One of the benefits is that identifier lookup does not need to take scopes into account
|
||
|
|
and we can basically ignore the result of the analysis phase.
|
||
|
|
|
||
|
|
All subsequent stages have the property that all names stay unique. This means if
|
||
|
|
a new identifier needs to be introduced, a new unique name is generated.
|
||
|
|
|
||
|
|
## Function Hoister
|
||
|
|
|
||
|
|
The function hoister moves all function definitions to the topmost block. This is
|
||
|
|
a semantically equivalent transformation as long as it is performed after the
|
||
|
|
disambiguation stage. The reason is that moving a definition upwards cannot decrease
|
||
|
|
its visibility and it is impossible to reference variables defined in a different function.
|
||
|
|
|
||
|
|
The benefit of this stage is that function definitions can be lookup up more easily.
|
||
|
|
|
||
|
|
## Function Grouper
|
||
|
|
|
||
|
|
The function grouper has to be applied after the disambiguator and the function hoister.
|
||
|
|
Its effect is that all topmost elements that are not function definitions are moved
|
||
|
|
into a single block which is the first satement of the root block.
|
||
|
|
|
||
|
|
After this step, a program has the following normal form:
|
||
|
|
|
||
|
|
{ I F... }
|
||
|
|
|
||
|
|
Where I is a block that does not contain any function definitions (not even recursively)
|
||
|
|
and F is a list of function definitions such that no function contains a function definition.
|
||
|
|
|
||
|
|
## Functional Inliner
|
||
|
|
|
||
|
|
The functional inliner depends on the disambiguator, the function hoister and function grouper.
|
||
|
|
It performs function inlining such that the result of the inlining is an expression. This can
|
||
|
|
only be done if the body of the function to be inlined has the form ``{ r := E }`` where ``r``
|
||
|
|
is the single return value of the function, ``E`` is an expression and all arguments in the
|
||
|
|
function call are so-called movable expressions. A movable expression is either a literal, a
|
||
|
|
variable or a function call (or EVM opcode) which does not have side-effects and also does not
|
||
|
|
depend on any side-effects.
|
||
|
|
|
||
|
|
As an example, neither ``mload`` nor ``mstore`` would be allowed.
|
||
|
|
|
||
|
|
## Full Function Inliner
|
||
|
|
|
||
|
|
## Variable Eliminator
|
||
|
|
|
||
|
|
## Unused Declaration Pruner
|
||
|
|
|
||
|
|
## Function Unifier
|