sys_core_fold: Remove problematic optimization

[bjorng]

The optimization of nested lets was unsafe if the number of iterations for sys_core_fold ran out. There have been several attempts to fix that problem:

5076069 (#6624)
30d4c45 (#6631)
ff05bee (#6575)

It's time to cut the Gordian knot by removing the optimization. While at it, remove all optimizations of nested lets, not only the offending part of the optimization.

Running scripts/diffable before and after and diffing, shows changes in 40 modules. Most of them are neutral (the same instructions in a different order). There are few changes where an extra test_heap instruction has been introduced, for example in the compile module:

-    {test_heap,19,1}.
+    {test_heap,15,1}.
     {update_record,{atom,reuse},14,{y,0},{x,0},{list,[7,{x,0}]}}.
-    {put_tuple2,{x,0},{list,[{atom,ok},{y,1},{x,0}]}}.
     {try_end,{y,2}}.
+    {test_heap,4,1}.
+    {put_tuple2,{x,0},{list,[{atom,ok},{y,1},{x,0}]}}.
     {deallocate,3}.
     return.

which was compiled from this source code:

try
    Mod = cerl:concrete(cerl:module_name(Core)),
    {ok,Core,St#compile{module=Mod}}
catch
    _:_ ->
        {ok,Core,St}
end.

In the ct_run module, the following code:

case proplists:get_value(step, Misc) of
    undefined ->
        #opts{};
    StepOpts ->
        #opts{step = StepOpts}
end

is no longer optimized to:

StepOpts = proplists:get_value(step, Misc)
#opts{step = StepOpts}

There are also improvements in a few modules.

Closes #6633
Closes #6635

[github-actions]

CT Test Results

No tests were run for this PR. This is either because the build failed, or the PR is based on a branch without GH actions tests configured.

Results for commit 19aa6b1

To speed up review, make sure that you have read Contributing to Erlang/OTP and that all checks pass.

See the TESTING and DEVELOPMENT HowTo guides for details about how to run test locally.

Artifacts

• Complete CT logs (Download Logs)
• No HTML docs found
• No Windows Installer found

// Erlang/OTP Github Action Bot

[bjorng]

I have included a commit authored by @jhogberg that enhances an existing optimization so that the extra test_heap instructions are avoided.