[WebAssembly] Unstackify regs after fixing unwinding mismatches


[WebAssembly] Unstackify regs after fixing unwinding mismatches

Fixing unwind mismatches for exception handling can result in splicing
existing BBs and moving some of instructions to new BBs. In this case
some of stackified def registers in the original BB can be used in the
split BB. For example, we have this BB and suppose %r0 is a stackified

  %r0 = call @foo
  ... use %r0 ...

After fixing unwind mismatches in CFGStackify, bb.1 can be split and
some instructions can be moved to a newly created BB:

  %r0 = call @foo

bb.split (new):
  ... use %r0 ...

In this case we should make %r0 un-stackified, because its use is now in
another BB.

When spliting a BB, this CL unstackifies all def registers that have
uses in the new split BB.

Reviewers: dschuff

Subscribers: sbc100, jgravelle-google, hiraditya, sunfish, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D68218