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Optimize byte-after-shr for shift amounts that are not multiples of 8.

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This commit is contained in:
chriseth 2020-08-04 11:25:09 +02:00
parent f079efe28c
commit a3a9630d8b
3 changed files with 11 additions and 7 deletions
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4
libevmasm/RuleList.h
View File

@ -583,9 +583,7 @@ std::vector<SimplificationRule<Pattern>> simplificationRuleListPart7(
Builtins::BYTE(A, Builtins::SHR(B, X)),
[=]() -> Pattern { return Word(0); },
true,
[=] {
return B.d() % 8 == 0 && A.d() < Pattern::WordSize / 8 && B.d() <= Pattern::WordSize && A.d() < B.d() / 8;
}
[=] { return A.d() < B.d() / 8; }
});
rules.push_back({

5
test/formal/combine_byte_shr_2.py
View File

@ -3,7 +3,7 @@ from opcodes import *
"""
byte(A, shr(B, X))
given B % 8 == 0 && A < n_bits/8 && B <= n_bits && A < B / 8
given A < B / 8
->
0
"""
@ -22,9 +22,6 @@ nonopt = BYTE(A, SHR(B, X))
# Optimized result
opt = 0
rule.require(B % 8 == 0)
rule.require(ULT(A, n_bits/8))
rule.require(ULE(B, n_bits))
rule.require(ULT(A, DIV(B,8)))
rule.check(nonopt, opt)

9
test/libyul/yulOptimizerTests/expressionSimplifier/byte_after_shr_non_mul_of_8.yul Normal file
View File

@ -0,0 +1,9 @@
{
sstore(0, byte(0, shr(0x9, calldataload(0))))
}
// ====
// EVMVersion: >=constantinople
// ----
// step: expressionSimplifier
//
// { sstore(0, 0) }