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Merge pull request #6935 from ethereum/subMaxValueXNotXRule

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Add optimization rule SUB(~0, X) -> NOT(X).
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chriseth 2019-06-17 14:42:49 +02:00 committed by GitHub
commit 633510eb04
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1
Changelog.md
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@ -5,6 +5,7 @@ Language Features:
Compiler Features:
* Optimizer: Add rule to simplify SUB(~0, X) to NOT(X).

1
libevmasm/RuleList.h
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@ -123,6 +123,7 @@ std::vector<SimplificationRule<Pattern>> simplificationRuleListPart2(
{{Instruction::ADD, {X, 0}}, [=]{ return X; }, false},
{{Instruction::ADD, {0, X}}, [=]{ return X; }, false},
{{Instruction::SUB, {X, 0}}, [=]{ return X; }, false},
{{Instruction::SUB, {~u256(0), X}}, [=]() -> Pattern { return {Instruction::NOT, {X}}; }, false},
{{Instruction::MUL, {X, 0}}, [=]{ return u256(0); }, true},
{{Instruction::MUL, {0, X}}, [=]{ return u256(0); }, true},
{{Instruction::MUL, {X, 1}}, [=]{ return X; }, false},

26
test/formal/sub_not_zero_x_to_not_x_256.py Normal file
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@ -0,0 +1,26 @@
from rule import Rule
from opcodes import *
"""
Rule:
SUB(~0, X) -> NOT(X)
Requirements:
"""
rule = Rule()
n_bits = 256
# Input vars
X = BitVec('X', n_bits)
# Constants
ZERO = BitVecVal(0, n_bits)
# Non optimized result
nonopt = SUB(~ZERO, X)
# Optimized result
opt = NOT(X)
rule.check(nonopt, opt)