Panic on function call with >16 operands: call operand count exceeds SWAP16

[micahscopes]

Description

The EVM backend panics when lowering a function call with more than 16 arguments:

thread 'main' panicked at crates/codegen/src/stackalloc/stackify/sym_stack.rs:247:9:
call operand count exceeds SWAP16

Minimal Reproduction

fn many_params(
    _ a1: u256, _ a2: u256, _ a3: u256, _ a4: u256,
    _ a5: u256, _ a6: u256, _ a7: u256, _ a8: u256,
    _ a9: u256, _ a10: u256, _ a11: u256, _ a12: u256,
    _ a13: u256, _ a14: u256, _ a15: u256, _ a16: u256,
    _ a17: u256,
) -> u256 {
    let sum = a1 + a2 + a3 + a4 + a5 + a6 + a7 + a8
    sum + a9 + a10 + a11 + a12 + a13 + a14 + a15 + a16 + a17
}

pub contract Crash {
    init() {}
    recv TestMsg {
        Test {} -> u256 {
            many_params(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
        }
    }
}

16 params works. 17 panics.

Impact

This blocks typed EC pairing wrappers (BN254 4-pair pairing needs 24 u256 args) and any function with a wide parameter list. The workaround is to pass data through memory instead of as function arguments.

Expected behavior

The compiler should either:

1. Automatically spill excess arguments to memory, or
2. Emit a clear error diagnostic instead of panicking

Environment

• Fe: v26.0.0-alpha.7
• Sonatina: bfa66a0