[PATCH] D153674: [dataflow] Disallow implicit copy of Environment, use fork() instead

[Sam McCall via Phabricator via cfe-commits]

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Environments are heavyweight, and copies are observably different from the
original: they introduce new SAT variables, which degrade performance &
debugging. Copies should only be done deliberately, where justified.

Empirically there are several places in the framework where we perform dubious
copies, sometimes entirely accidentally. (see e.g. D153491 <https://reviews.llvm.org/D153491>). Making these
explicit makes this mistake harder.

This patch forces copies to go through fork(), the copy-constructor is private.
This requires changes to existing callsites: some are correct and call fork(),
some are incorrect and are fixed, others are difficult and I left a FIXME.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D153674

Files:
  clang/include/clang/Analysis/FlowSensitive/DataflowAnalysis.h
  clang/include/clang/Analysis/FlowSensitive/DataflowEnvironment.h
  clang/include/clang/Analysis/FlowSensitive/TypeErasedDataflowAnalysis.h
  clang/lib/Analysis/FlowSensitive/DataflowEnvironment.cpp
  clang/lib/Analysis/FlowSensitive/Transfer.cpp
  clang/lib/Analysis/FlowSensitive/TypeErasedDataflowAnalysis.cpp
  clang/unittests/Analysis/FlowSensitive/TestingSupport.h

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