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Optimize obsolete ANDs in combination with certain SHIFTs

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Mathias Baumann
2019-03-29 10:08:05 +01:00
parent 84fbf605aa
commit 5c66ccc179
3 changed files with 103 additions and 0 deletions
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libevmasm/RuleList.h
+24
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@@ -391,6 +391,30 @@ std::vector<SimplificationRule<Pattern>> simplificationRuleListPart7(
false
});
std::function<bool()> feasibilityFunction = [=]() {
if (B.d() > 256)
return false;
unsigned bAsUint = static_cast<unsigned>(B.d());
return (A.d() & (u256(-1) >> bAsUint)) == (u256(-1) >> bAsUint);
};
rules.push_back({
// AND(A, SHR(B, X)) -> A & ((2^256-1) >> B) == ((2^256-1) >> B)
{Instruction::AND, {A, {Instruction::SHR, {B, X}}}},
[=]() -> Pattern { return {Instruction::SHR, {B, X}}; },
false,
feasibilityFunction
});
rules.push_back({
// AND(SHR(B, X), A) -> ((2^256-1) >> B) & A == ((2^256-1) >> B)
{Instruction::AND, {{Instruction::SHR, {B, X}}, A}},
[=]() -> Pattern { return {Instruction::SHR, {B, X}}; },
false,
feasibilityFunction
});
return rules;
}