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Fix ExpressionSplitter example

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Fix error (0x123 and 0x456 were swapped) and split constants into expressions
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Tynan Richards 2021-11-24 14:39:14 +01:00 committed by chriseth
parent 71f8576b86
commit d56fb3afff
1 changed files with 9 additions and 6 deletions
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15
docs/internals/optimizer.rst
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@ -521,7 +521,7 @@ ExpressionSplitter
The expression splitter turns expressions like ``add(mload(0x123), mul(mload(0x456), 0x20))`` The expression splitter turns expressions like ``add(mload(0x123), mul(mload(0x456), 0x20))``
into a sequence of declarations of unique variables that are assigned sub-expressions into a sequence of declarations of unique variables that are assigned sub-expressions
of that expression so that each function call has only variables or literals of that expression so that each function call has only variables
as arguments. as arguments.
The above would be transformed into The above would be transformed into
@ -529,10 +529,13 @@ The above would be transformed into
.. code-block:: yul .. code-block:: yul
{ {
let _1 := mload(0x123) let _1 = 0x20
let _2 := mul(_1, 0x20) let _2 = 0x456
let _3 := mload(0x456) let _3 = mload(_2)
let z := add(_3, _2) let _4 = mul(_3, _1)
let _5 = 0x123
let _6 = mload(_5)
let z = add(_6, _4)
} }
Note that this transformation does not change the order of opcodes or function calls. Note that this transformation does not change the order of opcodes or function calls.
@ -543,7 +546,7 @@ this "outlining" of the inner expressions in all cases. We can sidestep this lim
The final program should be in a form such that (with the exception of loop conditions) The final program should be in a form such that (with the exception of loop conditions)
function calls cannot appear nested inside expressions function calls cannot appear nested inside expressions
and all function call arguments have to be literals or variables. and all function call arguments have to be variables.
The benefits of this form are that it is much easier to re-order the sequence of opcodes The benefits of this form are that it is much easier to re-order the sequence of opcodes
and it is also easier to perform function call inlining. Furthermore, it is simpler and it is also easier to perform function call inlining. Furthermore, it is simpler