ICE in the codegen when using .slot on a mapping reference in assembly: InternalCompilerError: Invalid stack item name: slot

[emo-eth]

Description

Sometimes compiling via IR results in the following error (with Foundry):

❯ forge build
[⠆] Compiling...
[⠆] Compiling 69 files with 0.8.15
[⠔] Solc 0.8.15 finished in 3.00s
Error: 
Compiler run failed
InternalCompilerError: Invalid stack item name: slot

As the error implies, it seems to be related to storing variables that point to storage slots.

Environment

• Compiler version: reproduced with 0.8.15,0.8.14,0.8.13
• Framework/IDE (e.g. Truffle or Remix): Foundry
• EVM execution environment / backend / blockchain client: Foundry
• Operating system: macOS

Steps to Reproduce

In my case, I was able to resolve this by changing the following code from this:

        mapping(uint256 => address) storage tokenApprovalsPtr = _tokenApprovals;
        // The following is equivalent to `approvedAddress = _tokenApprovals[tokenId]`.
        assembly {
            // Compute the slot.
            mstore(0x00, tokenId)
            mstore(0x20, tokenApprovalsPtr.slot)
            approvedAddressSlot := keccak256(0x00, 0x40)
            // Load the slot's value from storage.
            approvedAddress := sload(approvedAddressSlot)
        }

to this:

        // The following is equivalent to `approvedAddress = _tokenApprovals[tokenId]`.
        assembly {
            // Compute the slot.
            mstore(0x00, tokenId)
            mstore(0x20, _tokenApprovals.slot)
            approvedAddressSlot := keccak256(0x00, 0x40)
            // Load the slot's value from storage.
            approvedAddress := sload(approvedAddressSlot)
        }

Link to commit with issue present: https://github.com/jameswenzel/bound-layerable/blob/91b7096cfedd20bb422f5ed1f83c7e50261c2bcc/src/token/ERC721A.sol#L694
Link to commit with issue fixed: https://github.com/jameswenzel/bound-layerable/blob/770ded9df31d624f38e1db6c32d0d5c6f7e64132/src/token/ERC721A.sol#L694

While the code I changed is copied from the ERC721A repo, I'm able to build the code at that commit as-is without issues, with the IR pipeline enabled.

[cameel]

Thanks for the report! This indeed seems to be a bug in the compiler. I managed to create a smaller repro (see below). Simply using .slot on a storage reference to a mapping in assembly triggers it.

Looks like the bug has been there all the way since the IR was introduced (or at least the --ir option) in 0.5.8. Back then the syntax was _slot, not .slot though. Between 0.5.10 and 0.7.0 it was causing an uncaught exception in map::at() but starting with 0.7.1 it's again an ICE.

Repro

test.sol:

contract C  {
    mapping(uint => uint) private m;

    function g() public {
        mapping(uint => uint) storage mPtr = m;
        assembly {
            pop(mPtr.slot)
        }
    }
}

solc test.sol --ir

Internal compiler error:
/solidity/libsolidity/codegen/ir/IRVariable.cpp(52): Throw in function solidity::frontend::IRVariable solidity::frontend::IRVariable::part(const std::string&) const
Dynamic exception type: boost::wrapexcept<solidity::langutil::InternalCompilerError>
std::exception::what: Invalid stack item name: slot
[solidity::util::tag_comment*] = Invalid stack item name: slot