Make execution tractable #47
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The previous approach to exploring conditional branches meant that contracts with nested conditionals would experience a combinatorial explosion in the number of virtual machine threads waiting to execute. This commit introduces a new approach that ensures that all instructions in the bytecode are visited, but not all paths to all of those instructions are executed. This drastically cuts the program state space while still ensuring that we gather the required information. This is done by imposing a (configurable) limit on the number of times a given `JUMPDEST` can be jumped to by `JUMPI` instructions. Normal `JUMP` instructions will always proceed as usual as they do not cause a bifurcation in the state space.
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kustosz
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Aug 7, 2023
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Summary
The previous approach to exploring conditional branches meant that contracts with nested conditionals would experience a combinatorial explosion in the number of virtual machine threads waiting to execute.
This commit introduces a new approach that ensures that all instructions in the bytecode are visited, but not all paths to all of those instructions are executed. This drastically cuts the program state space while still ensuring that we gather the required information.
This is done by imposing a (configurable) limit on the number of times a given
JUMPDESTcan be jumped to byJUMPIinstructions. NormalJUMPinstructions will always proceed as usual as they do not cause a bifurcation in the state space.Closes #44
Details
So while it was manifesting as a hang, the analyzer was indeed making work. The issue was that it was producing new branches to evaluate faster than it could consume them. This is now fixed.
Checklist