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Access output memory area so that we do not pay for resize during call.

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This commit is contained in:
chriseth 2016-09-16 12:56:52 +02:00
parent dd2f878e59
commit 5a45990458
2 changed files with 14 additions and 5 deletions
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17
libsolidity/codegen/ExpressionCompiler.cpp
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@ -1476,6 +1476,18 @@ void ExpressionCompiler::appendExternalFunctionCall(
utils().storeFreeMemoryPointer();
}
// Touch the end of the output area so that we do not pay for memory resize during the call
// (which we would have to subtract from the gas left)
// We could also just use MLOAD; POP right before the gas calculation, but the optimizer
// would remove that, so we use MSTORE here.
if (!_functionType.gasSet() && retSize > 0)
{
m_context << u256(0);
utils().fetchFreeMemoryPointer();
// This touches too much, but that way we save some rounding arithmetics
m_context << u256(retSize) << Instruction::ADD << Instruction::MSTORE;
}
// Copy function identifier to memory.
utils().fetchFreeMemoryPointer();
if (!_functionType.isBareCall() || manualFunctionId)
@ -1551,10 +1563,7 @@ void ExpressionCompiler::appendExternalFunctionCall(
gasNeededByCaller += eth::GasCosts::callValueTransferGas;
if (!isCallCode && !isDelegateCall && !existenceChecked)
gasNeededByCaller += eth::GasCosts::callNewAccountGas; // we never know
m_context <<
gasNeededByCaller <<
Instruction::GAS <<
Instruction::SUB;
m_context << gasNeededByCaller << Instruction::GAS << Instruction::SUB;
}
if (isDelegateCall)
m_context << Instruction::DELEGATECALL;

2
test/libsolidity/SolidityEndToEndTest.cpp
View File

@ -7191,7 +7191,7 @@ BOOST_AUTO_TEST_CASE(mem_resize_is_not_paid_at_call)
// This tests that memory resize for return values is not paid during the call, which would
// make the gas calculation overly complex. We access the end of the output area before
// the call is made.
// Tests that this also survivecs the optimizer.
// Tests that this also survives the optimizer.
char const* sourceCode = R"(
contract C {
function f() returns (uint[200]) {}