• Austin Seipp's avatar
    compiler: make sure we reject -O + HscInterpreted · b199536b
    Austin Seipp authored
    When using GHCi, we explicitly reject optimization, because the
    compilers optimization passes can introduce unboxed tuples, which the
    interpreter is not able to handle. But this goes the other way too: using
    GHCi on optimized code may cause the optimizer to float out breakpoints
    that the interpreter introduces. This manifests itself in weird ways,
    particularly if you as an API client use custom DynFlags to introduce
    optimization in combination with HscInterpreted.
    
    It turns out we weren't checking for consistent DynFlag settings when
    doing `setSessionDynFlags`, as #10052 showed. While the main driver
    handled it in `DynFlags` via `parseDynamicFlags`, we didn't check this
    elsewhere.
    
    This does a little refactoring to split out some of the common code, and
    immunizes the various `DynFlags` utilities in the `GHC` module from this
    particular bug. We should probably be checking other general invariants
    too.
    
    This fixes #10052, and adds some notes about the behavior in `GHC` and
    `FloatOut`
    
    As a bonus, expose `warningMsg` from `ErrUtils` as a helper since it
    didn't exist (somehow).
    Signed-off-by: default avatarAustin Seipp <austin@well-typed.com>
    
    Reviewed By: edsko
    
    Differential Revision: https://phabricator.haskell.org/D727
    
    GHC Trac Issues: #10052
    b199536b
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