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Mask generator optimizations #15935

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40cf83e
constant optimizer assembly tests
May 7, 2025
4170f4f
constant optimizer: a semantic test
Apr 23, 2025
198d290
formatting and comments
May 16, 2025
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3 changes: 2 additions & 1 deletion Changelog.md
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Original file line number Diff line number Diff line change
@@ -4,6 +4,8 @@ Language Features:

Compiler Features:
* ethdebug: Experimental support for instructions and source locations under EOF.
* Constant Optimizer: Compute masks using shifts when optimizing for size; use an ``--optimizer-runs`` value less than 200 for maximum size reduction.


Bugfixes:

@@ -13,7 +15,6 @@ Compiler Features:
* EVM: Set default EVM Version to `prague`.
* NatSpec: Capture Natspec documentation of `enum` values in the AST.


Bugfixes:
* SMTChecker: Do not consider loop conditions as constant-condition verification target as this could cause incorrect reports and internal compiler errors.
* SMTChecker: Fix incorrect analysis when only a subset of contracts is selected with `--model-checker-contracts`.
36 changes: 35 additions & 1 deletion libevmasm/ConstantOptimiser.cpp
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@cameel cameel Mar 15, 2025 •
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@ekpyron Not strictly related to the PR, but while looking at it I noticed that ConstantOptimisationMethod::simpleRunGas() does not account for the new AssemblyItem types we introduced for EOF.

Especially DUPN and SWAPN. Though fortunately it should not have any real consequences because we are not using them in constant optimizer yet (heads up @rodiazet).

Original file line number Diff line number Diff line change
@@ -253,7 +253,41 @@ AssemblyItems ComputeMethod::findRepresentation(u256 const& _value)
if (_value < 0x10000)
// Very small value, not worth computing
return AssemblyItems{_value};
else if (numberEncodingSize(~_value) < numberEncodingSize(_value))

// check for masks first
// high ones low zeros
// |----------||--------------|
// 0x000000000000000000000000000000000000ffffffffffff0000000000000000
unsigned lowZeros = 0;
unsigned highOnes = 0;
while (((_value >> lowZeros) & 1) == 0 && lowZeros < 256)
++lowZeros;
while (((_value >> (lowZeros + highOnes)) & 1) == 1 && highOnes < 256)
++highOnes;
if (
m_params.evmVersion.hasBitwiseShifting() &&
highOnes > 32 && // push would be more efficient otherwise
((_value >> (lowZeros + highOnes)) == 0) && // this is a pure mask
((lowZeros + highOnes < 256) || lowZeros > 16) // otherwise negation is more effective
)
{
// this is a big enough mask to use zero negation
AssemblyItems newRoutine = AssemblyItems{u256(0), Instruction::NOT};
if ((highOnes + lowZeros) != 256)
newRoutine += AssemblyItems{u256(256 - highOnes), Instruction::SHR};
if (lowZeros > 0)
newRoutine += AssemblyItems{u256(lowZeros), Instruction::SHL};
return newRoutine;
}
// pure negation can sometimes produce bad results
// example: 0xff00000000000000000000000000000000000000000000000000000000000000
// 0xff at the most significant byte of u256
// without the extra condition: not(sub(shl(0xf8, 0x01), 0x01))
// the extra condition turns that into: shl(0xf8, 0xff)
if (
numberEncodingSize(~_value) < numberEncodingSize(_value) &&
(lowZeros+highOnes < 256 || highOnes > 16)
)
// Negated is shorter to represent
return findRepresentation(~_value) + AssemblyItems{Instruction::NOT};
else
4 changes: 2 additions & 2 deletions test/cmdlineTests/optimizer_BlockDeDuplicator/output
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Original file line number Diff line number Diff line change
@@ -7,11 +7,11 @@ EVM assembly:
0x00
dup1
sload
not(sub(shl(0x40, 0x01), 0x01))
shl(0x40, not(0x00))
and
/* "input.sol":201:206 fun_x */
or(tag_0_7, shl(0x20, tag_2))
sub(shl(0x40, 0x01), 0x01)
shr(0xc0, not(0x00))
/* "input.sol":179:210 function() r = true ? fun_x : f */
and
or
2 changes: 1 addition & 1 deletion test/cmdlineTests/optimizer_inliner_dynamic_reference/output
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Original file line number Diff line number Diff line change
@@ -84,7 +84,7 @@ sub_0: assembly {
/* "input.sol":147:152 x = f */
dup1
sload
not(0xffffffffffffffff)
shl(0x40, not(0x00))
and
/* "input.sol":151:152 f */
tag_17
4 changes: 2 additions & 2 deletions test/cmdlineTests/optimizer_inliner_dynamic_reference_constructor/output
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Original file line number Diff line number Diff line change
@@ -17,11 +17,11 @@ tag_1:
/* "input.sol":93:98 x = f */
dup1
sload
not(sub(shl(0x40, 0x01), 0x01))
shl(0x40, not(0x00))
and
/* "input.sol":97:98 f */
or(tag_0_12, shl(0x20, tag_4))
sub(shl(0x40, 0x01), 0x01)
shr(0xc0, not(0x00))
/* "input.sol":93:98 x = f */
and
or
8 changes: 4 additions & 4 deletions test/cmdlineTests/standard_debug_info_in_evm_asm_via_ir_location/output.json
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Original file line number Diff line number Diff line change
@@ -20,7 +20,7 @@
dup4
add
swap2
sub(shl(0x40, 0x01), 0x01)
shr(0xc0, not(0x00))
dup4
gt
dup5
@@ -104,7 +104,7 @@ sub_0: assembly {
jumpi(tag_26, callvalue)
jumpi(tag_26, slt(add(not(0x03), calldatasize), 0x00))
sload(0x00)
sub(shl(0xff, 0x01), 0x01)
shr(0x01, not(0x00))
dup2
eq
tag_14
@@ -350,7 +350,7 @@ sub_0: assembly {
dup4
add
swap2
sub(shl(0x40, 0x01), 0x01)
shr(0xc0, not(0x00))
dup4
gt
dup5
@@ -450,7 +450,7 @@ sub_0: assembly {
jumpi(tag_26, callvalue)
jumpi(tag_26, slt(add(not(0x03), calldatasize), 0x00))
sload(0x00)
sub(shl(0xff, 0x01), 0x01)
shr(0x01, not(0x00))
dup2
eq
tag_14
4 changes: 2 additions & 2 deletions test/cmdlineTests/viair_subobject_optimization/output
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Original file line number Diff line number Diff line change
@@ -18,7 +18,7 @@ EVM assembly:
dup4
add
swap2
sub(shl(0x40, 0x01), 0x01)
shr(0xc0, not(0x00))
dup4
gt
dup5
@@ -223,7 +223,7 @@ sub_0: assembly {
dup4
add
swap2
sub(shl(0x40, 0x01), 0x01)
shr(0xc0, not(0x00))
dup4
gt
dup5
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