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Add constant optimiser for SHR/SHL instructions

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Alex Beregszaszi 2017-05-10 10:46:44 +01:00
parent fe61435c27
commit cb352edd26
2 changed files with 11 additions and 0 deletions
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1
Changelog.md
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@ -6,6 +6,7 @@ Features:
* Commandline interface: Error when missing or inaccessible file detected. Suppress it with the ``--ignore-missing`` flag.
* General: Support accessing dynamic return data in post-byzantium EVMs.
* Interfaces: Allow overriding external functions in interfaces with public in an implementing contract.
* Optimizer: Optimize ``SHL`` and ``SHR`` only involving constants (Constantinople only).
* Optimizer: Remove useless ``SWAP1`` instruction preceding a commutative instruction (such as ``ADD``, ``MUL``, etc).
* Optimizer: Replace comparison operators (``LT``, ``GT``, etc) with opposites if preceded by ``SWAP1``, e.g. ``SWAP1 LT`` is replaced with ``GT``.
* Optimizer: Optimize across ``mload`` if ``msize()`` is not used.

10
libevmasm/RuleList.h
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@ -89,6 +89,16 @@ std::vector<SimplificationRule<Pattern>> simplificationRuleList(
u256 mask = (u256(1) << testBit) - 1;
return u256(boost::multiprecision::bit_test(B.d(), testBit) ? B.d() | ~mask : B.d() & mask);
}, false},
{{Instruction::SHL, {A, B}}, [=]{
if (A.d() > 255)
return u256(0);
return u256(bigint(B.d()) << unsigned(A.d()));
}, false},
{{Instruction::SHR, {A, B}}, [=]{
if (A.d() > 255)
return u256(0);
return B.d() >> unsigned(A.d());
}, false},
// invariants involving known constants
{{Instruction::ADD, {X, 0}}, [=]{ return X; }, false},