Remove bytecode duplication

[GorogPeter]

I found that the parser duplicates move instructions at the end of blocks in some cases.

For example:

(module
  (func (result i32 i32 i32)
    (block (result i32 i32 i32)
      i32.const 1
      i32.const 2
      i32.const 3
    )
  )
)

Results this:

required stack size: 48 bytes
stack: [(constant 1, i32, pos 0) (constant 2, i32, pos 8) (constant 3, i32, pos 16) ....]
bytecode size: 168 bytes

     0 const32 dstOffset: 0 value: 1
    16 const32 dstOffset: 8 value: 2
    32 const32 dstOffset: 16 value: 3
    48 move32 srcOffset: 0 dstOffset: 24 
    64 move32 srcOffset: 8 dstOffset: 32 
    80 move32 srcOffset: 16 dstOffset: 40 
    96 move32 srcOffset: 16 dstOffset: 40 
   112 move32 srcOffset: 8 dstOffset: 32 
   128 move32 srcOffset: 0 dstOffset: 24 
   144 end resultOffsets: 24 32 40

The duplication occures in keepBlockResultsIfNeeds(...) function, here and here.

By removing the first one (with the if statement), it does not duplicate the bytecode:

required stack size: 48 bytes
stack: [(constant 1, i32, pos 0) (constant 2, i32, pos 8) (constant 3, i32, pos 16) ....]
bytecode size: 120 bytes

     0 const32 dstOffset: 0 value: 1
    16 const32 dstOffset: 8 value: 2
    32 const32 dstOffset: 16 value: 3
    48 move32 srcOffset: 16 dstOffset: 40 
    64 move32 srcOffset: 8 dstOffset: 32 
    80 move32 srcOffset: 0 dstOffset: 24 
    96 end resultOffsets: 24 32 40

It also passes the tests and the benchmark tests as well.

But unfortunately, I'm not completely aware of the impact of this change on Walrus. Could someone help me, please?

[ksh8281]

IMO you found good point!