create reference variable for offset and length in Yul

[eMarchenko]

Describe the issue:

write-after-write detector falsely reacts on assembly work with calldata:

Code example to reproduce the issue:

function foo(bytes calldata cd) private pure returns (bytes calldata signature)
{
    assembly {
        let ptr := add(cd.offset, calldataload(cd.offset))
        signature.offset := add(ptr, 0x20)
        signature.length := calldataload(ptr)
    }
}

Version:

^0.9 - tool was run on other machine

Relevant log output:

No response

[0xalpharush]

It looks like the IR doesn't currently create a reference to each member of signature, offset and length. This would need to be added to eliminate this false positive.

Contract Test
	Function Test.foo(bytes) (*)
		Expression: ptr_foo_asm_0 = cd + calldataload(uint256)(cd)
		IRs:
			TMP_0(uint256) = SOLIDITY_CALL calldataload(uint256)(cd)
			TMP_1(bytes) = cd + TMP_0
			ptr_foo_asm_0(uint256) := TMP_1(bytes)
		Expression: signature = ptr_foo_asm_0 + 0x20
		IRs:
			TMP_2(uint256) = ptr_foo_asm_0 + 32
			signature(bytes) := TMP_2(uint256)
		Expression: signature = calldataload(uint256)(ptr_foo_asm_0)
		IRs:
			TMP_3(uint256) = SOLIDITY_CALL calldataload(uint256)(ptr_foo_asm_0)
			signature(bytes) := TMP_3(uint256)

foo.sol analyzed (1 contracts)