1. 20 Jul, 2015 1 commit
    • danno's avatar
      [turbofan]: Add a context relaxation Reducer · cca5e74a
      danno authored
      In many cases, the context that TurboFan's ASTGraphBuilder or subsequent
      reduction operations attaches to nodes does not need to be that exact
      context, but rather only needs to be one with the same native context,
      because it is used internally only to fetch the native context, e.g. for
      creating and throwing exceptions.
      
      This reducer recognizes common cases where the context that is specified
      for a node can be relaxed to a canonical, less specific one. This
      relaxed context can either be the enclosing function's context or a specific
      Module or Script context that is explicitly created within the function.
      
      This optimization is especially important for TurboFan-generated code stubs
      which use context specialization and inlining to generate optimal code.
      Without context relaxation, many extraneous moves are generated to pass
      exactly the right context to internal functions like ToNumber and
      AllocateHeapNumber, which only need the native context. By turning context
      relaxation on, these moves disappear because all these common internal
      context uses are unified to the context passed into the stub function, which
      is typically already in the correct context register and remains there for
      short stubs. It also eliminates the explicit use of a specialized context
      constant in the code stub in these cases, which could cause memory leaks.
      
      Review URL: https://codereview.chromium.org/1244583003
      
      Cr-Commit-Position: refs/heads/master@{#29763}
      cca5e74a