sys_core_fold: Remove an unsafe optimization

`sys_core_fold` has an optimization of repeated pattern matching.
For example, when a record is matched the first time, the pattern
is remembered. When the same record is matched again, the matching
does not need to be repeated, but the variables bound in the first
matching can be re-used.

It turns out that that there is a name capture problem when the old
inliner is used. The old inliner is used when explicitly inling
certain functions, and by the compiler test suites for testing the
compiler.

The name capture problem could be eliminated by more aggressive
variable renaming when inlining.

But, fortunately, given the new SSA passes, this optimization is no
longer as essential as it used to be. Removing the optimization
turns out to be mostly benefical, leading to a smaller stack
frame in many cases.

Also remove the optimizations of `element/2`, `is_record/3`, and
`setelement/3` from `sys_core_fold`. Because matched patterns are no
longer remembered, those optimizations can very rarely be applied any
more. (Those same optimizations are already done in `beam_ssa_type`.)

1 files changed, 5 insertions, 1 deletions

diff --git a/lib/compiler/src/beam_except.erl b/lib/compiler/src/beam_except.erl
index 09925b2872..28c89782c9 100644
--- a/lib/compiler/src/beam_except.erl
+++ b/lib/compiler/src/beam_except.erl
@@ -225,7 +225,11 @@ moves_from_stack(nil, I, Acc) ->
     {reverse(Acc),I};
 moves_from_stack({literal,[H|T]}, I, Acc) ->
     Cons = {cons,tag_literal(H),tag_literal(T)},
-    moves_from_stack(Cons, I, Acc).
+    moves_from_stack(Cons, I, Acc);
+moves_from_stack(_, _, _) ->
+    %% Not understood. Give up.
+    {[],-1}.
+
 
 get_reg(R, Regs) ->
     case Regs of