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Avoid unnecessary copies of arguments that are simple bindings #45380

Merged
merged 2 commits into from
Oct 26, 2017
Merged

Avoid unnecessary copies of arguments that are simple bindings #45380

merged 2 commits into from
Oct 26, 2017

Commits on Oct 26, 2017

  1. Avoid unnecessary copies of arguments that are simple bindings 

    Initially MIR differentiated between arguments and locals, which
introduced a need to add extra copies assigning the argument to a
local, even for simple bindings. This differentiation no longer exists,
but we're still creating those copies, bloating the MIR and LLVM IR we
emit.

Additionally, the current approach means that we create debug info for
both the incoming argument (marking it as an argument), and then
immediately shadow it a local that goes by the same name. This can be
confusing when using e.g. "info args" in gdb, or when e.g. a debugger
with a GUI displays the function arguments separately from the local
variables, especially when the binding is mutable, because the argument
doesn't change, while the local variable does.
    @dotdash
    dotdash committed Oct 26, 2017
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  2. Add comments to clarify function argument ownership

    @dotdash
    dotdash committed Oct 26, 2017
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