Optimize try/catch that ignores the return value

If a try/catch is used to ignore the potential exception caused by some
expression with a side effect such as:

   try
       side_effect()
   catch _Class:_Reason ->
        ok
   end,
   .
   .
   .

the generated code will be wasteful:

    try YReg TryLabel
    %% call side_effect() here
    try_end Yreg
    jump GoodLabel

  TryLabel:
    try_case YReg
    %% try_case has set up registers as follows:
    %% x(0) -> error | exit | throw
    %% x(1) -> reason
    %% x(2) -> raw stack trace data

  GoodLabel:
    %% This code does not use any x registers.

There will be two code paths that both end up at GoodLabel, and
the try_case instruction will set up registers that are never used.

We can do better by replacing try_case with try_end to obtain this
code:

    try YReg TryLabel
    %% call side_effect() here
    try_end Yreg
    jump GoodLabel

  TryLabel:
    try_end YReg

  GoodLabel:

The jump optimizer (beam_jump) can further optimize this code
like this:

    try YReg TryLabel
    %% call side_effect() here

  TryLabel:
    try_end YReg

0 files changed, 0 insertions, 0 deletions