article: Efficient gas calculation algorithm for EVM #123
Conversation
Codecov Report
@@ Coverage Diff @@
## master #123 +/- ##
=========================================
Coverage ? 99.88%
=========================================
Files ? 5
Lines ? 839
Branches ? 109
=========================================
Hits ? 838
Misses ? 1
Partials ? 0 |
chfast
requested review from
axic,
cdetrio,
chriseth,
gumb0,
halfalicious and
holiman
| A _basic block_ is a sequence of instructions that are executed "straight-line" | ||
| without being interrupted by jumps. I.e. they are nodes in the _control flow graph_. | ||
|
|
||
| The name "basic block" has been taken from LLVM. Other names are: just "block" |
There was a problem hiding this comment.
Isn't this just the generic term in compiler theory?
There was a problem hiding this comment.
I never had proper education in this field. If the term is well known, I should simplify this paragraph.
There was a problem hiding this comment.
Not sure about the well-known-ness, but llvm certainly did not introduce it :)
There was a problem hiding this comment.
I'd prefer if you called it 'basic segment', and talk about segments. Because we're talking about blockchains here, and in extension maybe doing paralell gas-calculation of future blocks, and things become a bit messy if we have two definitions for 'block'.
There was a problem hiding this comment.
This is pretty concrete term: https://en.wikipedia.org/wiki/Basic_block.
Maybe "basic instruction block" then?
| - `RETURN`, | ||
| - `REVERT`, | ||
| - `SELFDESTRUCT`, | ||
| - an instruction directly preceding `JUMPDEST`. |
There was a problem hiding this comment.
| - an instruction directly preceding `JUMPDEST`. | |
| - the last instruction in the program | |
| - an invalid instruction |
There was a problem hiding this comment.
We actually ignore invalid instructions by assuming they cost 0.
| - an instruction directly preceding `JUMPDEST`. | ||
|
|
||
| 2. The following instructions _start_ a basic block: | ||
| - `JUMPDEST`, |
There was a problem hiding this comment.
| - `JUMPDEST`, |
(this should be redundant together with the two rules below)
There was a problem hiding this comment.
I don't believe this is true. You can have a JUMPDEST anywhere.
There was a problem hiding this comment.
sure, but you say: a basic block starts right before ... an instruction directly after an intruction that has ended the previous basic block. And above: a basic block ends after ... an instruction directly preceding "jumpdest". Maybe just nitpicking :)
There was a problem hiding this comment.
I'm wondering about the attackability of this -- in hte case where a contract consists of 24k JUMPDESTs. I guess that's up to the implementation.
There was a problem hiding this comment.
I have a test/benchmark for this one. Other variations about it are definitely needed.
evmone's top speed is ~1Ggas/s. In this case where we do gas/stack checking for every instruction the execution is ~0.5Ggas/s.
The bigger problem is the analysis of this code takes ~0.1 ms what means it should cost ~1000 gas. This is the biggest concern so far.
Co-Authored-By: chriseth <chris@ethereum.org> Co-Authored-By: Andrei Maiboroda <andrei@ethereum.org>
chfast
force-pushed
the
docs_gas_algo
branch
from
8a700a5 to
1e703dd
Compare
TODO: