Truncates on constants aren't folded

[joss-aztec]

Aim

The test named poseidonsponge_x5_254 should pass

Expected Behavior

^

Bug

Compilation fails with:

After Constant Folding:
fn main f9 {
  b0(v0: [Field; 7]):
    v849 = cast Field 5 as u8
    v850 = truncate u8 68 to 8 bits, max_bit_size: 9
    v851 = mul v849, v850
    v852 = truncate v851 to 8 bits, max_bit_size: 16
    v853 = cast Field 340 as u8
    v854 = eq v852, v853
    constrain v854
    v855 = not Field 0
    constrain v855
    v856 = allocate
    store [Field 0, Field 0, Field 0, Field 0, Field 0] at v856
    v857 = allocate
    store Field 0 at v857
    v858 = eq v845, Field 3637726918731233354960448572465528704217843406233123660822069175839457651784
    constrain v858
    return unit 0
}

The application panicked (crashed).
Message:  internal error: entered unreachable code: ICE: Truncates are only ever applied to the result of a binary op
Location: crates/noirc_evaluator/src/ssa_refactor/acir_gen/mod.rs:486

Notice that v850 is a truncate performed on a numeric constant. This should instead be removed by constant folding and simplified to, in this case, u8 68.

To Reproduce

Installation Method

None

Nargo Version

No response

Additional Context

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Would you like to submit a PR for this Issue?

No

Support Needs

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[joss-aztec]

Also affects test named bit_shifts_comptime

[joss-aztec]

bit_shifts_comptime now passes following #1568. poseidonsponge_x5_254 fails for a different reason now.