Before this commit, `MakeEnvNullPass` was substituting uses of `env`
with uses of `nullptr`.
This operation was introducing undefined behavior, and subsequent
optimizations were allowed to mark BasicBlocks where it occured as
unreachable, eventually leading to their wrong removal.
This commit fixes the substitution, properly replacing loads from `env`
with `nullptr`.
This should never cause undefined behavior anymore, because the results
from load from `env` is never referenced in isolated functions.
This fixes an issue causing crashes when calling the public API
`decompileFunction`, that was internally adding a `MakeEnvNullPass`
(formerly a `ModulePass`) to a `FunctionPassManager.
This pass substitutes the `@env` global variable with a null pointer
`@env` is a pointer to the CPU state in QEMU, and is not meant to be
visible in the decompiled code.
This pass is used to remove all references to it before decompilation.
Pietro Fezzardi