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libsolidity/codegen: Use calldatacopy to cheaply zero memory instead of

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codecopy.

Motiviation:
  Zero'ing memory is commonplace in contracts, but with the upcoming
  Layer-2 EVM translation layers and other on-chain verification
  mechanisms, using `codecopy` becomes a `costly` operation in those
  sandboxes. Using `calldatacopy` achieves the same thing, gas costs
  are also the same as codecopy, and is significantly cheaper in the `sandbox` situation.
This commit is contained in:
pinkiebell 2020-01-22 17:49:15 +01:00
parent 29d7c7d065
commit bb6fb675e0
2 changed files with 2 additions and 2 deletions
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2
libsolidity/codegen/CompilerUtils.cpp
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@ -605,7 +605,7 @@ void CompilerUtils::zeroInitialiseMemoryArray(ArrayType const& _type)
Whiskers templ(R"({
let size := mul(length, <element_size>)
// cheap way of zero-initializing a memory range
codecopy(memptr, codesize(), size)
calldatacopy(memptr, calldatasize(), size)
memptr := add(memptr, size)
})");
templ("element_size", to_string(_type.memoryStride()));

2
test/libsolidity/SolidityEndToEndTest.cpp
View File

@ -10179,7 +10179,7 @@ BOOST_AUTO_TEST_CASE(create_dynamic_array_with_zero_length)
BOOST_AUTO_TEST_CASE(correctly_initialize_memory_array_in_constructor)
{
// Memory arrays are initialized using codecopy past the size of the code.
// Memory arrays are initialized using calldatacopy past the size of the calldata.
// This test checks that it also works in the constructor context.
char const* sourceCode = R"(
contract C {