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Merge pull request #7316 from ethereum/addByteOpt

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Replace byte(A, X) by zero if A >= 32
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chriseth 2019-09-02 10:50:26 +02:00 committed by GitHub
commit 3c963eb00e
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3 changed files with 25 additions and 0 deletions
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1
Changelog.md
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@ -5,6 +5,7 @@ Language Features:
Compiler Features: Compiler Features:
* Optimizer: Add rule that replaces the BYTE opcode by 0 if the first argument is larger than 31.
Bugfixes: Bugfixes:

8
libevmasm/RuleList.h
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@ -259,6 +259,14 @@ std::vector<SimplificationRule<Pattern>> simplificationRuleListPart5(
[=]() { return A.d() >= 256; } [=]() { return A.d() >= 256; }
}); });
// Replace BYTE(A, X), A >= 32 with 0
rules.push_back({
{Instruction::BYTE, {A, X}},
[=]() -> Pattern { return u256(0); },
true,
[=]() { return A.d() >= 32; }
});
for (auto const& op: std::vector<Instruction>{ for (auto const& op: std::vector<Instruction>{
Instruction::ADDRESS, Instruction::ADDRESS,
Instruction::CALLER, Instruction::CALLER,

16
test/libyul/yulOptimizerTests/expressionSimplifier/large_byte_access.yul Normal file
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@ -0,0 +1,16 @@
{
let a := calldataload(0)
let b := byte(33, a)
let c := byte(20, a)
// create cannot be removed.
let d := byte(33, create(0, 0, 0x20))
}
// ====
// step: expressionSimplifier
// ----
// {
// let a := calldataload(0)
// let b := 0
// let c := byte(20, a)
// let d := byte(33, create(0, 0, 0x20))
// }