Winch: Assertion failure with saturating conversion instructions

[alexcrichton]

Given this input:

(module
  (func (param f64 f64 f64 f64) (result f32 f64)
    f64.const 0
    local.get 0
    i64.const 0
    f64.const 0
    i64.const 0
    local.get 0
    f64.const 0
    i64.const 1
    i32.const 1
    i64.const 1
    f32.const 0
    local.get 0

    i32.const 0
    br_if 0

    drop
    drop
    drop
    drop
    drop
    drop
    i64.reinterpret_f64
    i64.const 0
    i64.xor
    drop
    drop
    drop
    drop
    drop
    drop
    f32.const 0
    f64.const 0
  )
)

since the implementation of saturating conversion instructions in #7909 this has panicked

$ cargo run --features winch --no-default-features --features compile compile -C compiler=winch ./testcase1.wasm -o /dev/null
...
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.06s
     Running `target/debug/wasmtime compile -C compiler=winch -o /dev/null ./foo.wat`
thread 'main' panicked at winch/codegen/src/codegen/context.rs:165:13:
assertion `left == right` failed
  left: 64
 right: 48
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

cc @saulecabrera

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[saulecabrera]

Thanks for catching this one Alex. I'll take a look.