brw_ir_analysis.h

/* -*- c++ -*- */
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#ifndef BRW_IR_ANALYSIS_H
#define BRW_IR_ANALYSIS_H

namespace brw {
   /**
    * Bitset of state categories that can influence the result of IR analysis
    * passes.
    */
   enum analysis_dependency_class {
      /**
       * The analysis doesn't depend on the IR, its result is effectively a
       * constant during the compilation.
       */
      DEPENDENCY_NOTHING = 0,
      /**
       * The analysis depends on the set of instructions in the program and
       * their naming.  Note that because instructions are named sequentially
       * by IP this implies a dependency on the control flow edges between
       * instructions.  This will be signaled whenever instructions are
       * inserted, removed or reordered in the program.
       */
      DEPENDENCY_INSTRUCTION_IDENTITY = 0x1,
      /**
       * The analysis is sensitive to the detailed semantics of instructions
       * in the program, where "detailed" means any change in the instruction
       * data structures other than the linked-list pointers (which are
       * already covered by DEPENDENCY_INSTRUCTION_IDENTITY).  E.g. changing
       * the negate or abs flags of an instruction source would signal this
       * flag alone because it would preserve all other instruction dependency
       * classes.
       */
      DEPENDENCY_INSTRUCTION_DETAIL = 0x2,
      /**
       * The analysis depends on the set of data flow edges between
       * instructions.  This will be signaled whenever the dataflow relation
       * between instructions has potentially changed, e.g. when the VGRF
       * index of an instruction source or destination changes (in which case
       * it will appear in combination with DEPENDENCY_INSTRUCTION_DETAIL), or
       * when data-dependent instructions are reordered (in which case it will
       * appear in combination with DEPENDENCY_INSTRUCTION_IDENTITY).
       */
      DEPENDENCY_INSTRUCTION_DATA_FLOW = 0x4,
      /**
       * The analysis depends on all instruction dependency classes.  These
       * will typically be signaled simultaneously when inserting or removing
       * instructions in the program (or if you're feeling too lazy to read
       * through your optimization pass to figure out which of the instruction
       * dependency classes above it invalidates).
       */
      DEPENDENCY_INSTRUCTIONS = 0x7,
      /**
       * The analysis depends on the set of VGRFs in the program and their
       * naming.  This will be signaled when VGRFs are allocated or released.
       */
      DEPENDENCY_VARIABLES = 0x8,
      /**
       * The analysis depends on the set of basic blocks in the program, their
       * control flow edges and naming.
       */
      DEPENDENCY_BLOCKS = 0x10,
      /**
       * The analysis depends on the program being literally the same (good
       * luck...), any change in the input invalidates previous analysis
       * computations.
       */
      DEPENDENCY_EVERYTHING = ~0
   };

   inline analysis_dependency_class
   operator|(analysis_dependency_class x, analysis_dependency_class y)
   {
      return static_cast<analysis_dependency_class>(
         static_cast<unsigned>(x) | static_cast<unsigned>(y));
   }
}

/**
 * Instantiate a program analysis class \p L which can calculate an object of
 * type \p T as result.  \p C is a closure that encapsulates whatever
 * information is required as argument to run the analysis pass.  The purpose
 * of this class is to make sure that:
 *
 *  - The analysis pass is executed lazily whenever it's needed and multiple
 *    executions are optimized out as long as the cached result remains marked
 *    up-to-date.
 *
 *  - There is no way to access the cached analysis result without first
 *    calling L::require(), which makes sure that the analysis pass is rerun
 *    if necessary.
 *
 *  - The cached result doesn't become inconsistent with the program for as
 *    long as it remains marked up-to-date. (This is only enforced in debug
 *    builds for performance reasons)
 *
 * The requirements on \p T are the following:
 *
 *  - Constructible with a single argument, as in 'x = T(c)' for \p c of type
 *    \p C.
 *
 *  - 'x.dependency_class()' on const \p x returns a bitset of
 *    brw::analysis_dependency_class specifying the set of IR objects that are
 *    required to remain invariant for the cached analysis result to be
 *    considered valid.
 *
 *  - 'x.validate(c)' on const \p x returns a boolean result specifying
 *    whether the analysis result \p x is consistent with the input IR.  This
 *    is currently only used for validation in debug builds.
 */
template<class T, class C>
class brw_analysis {
public:
   /**
    * Construct a program analysis.  \p c is an arbitrary object
    * passed as argument to the constructor of the analysis result
    * object of type \p T.
    */
   brw_analysis(const C *c) : c(c), p(NULL) {}

   /**
    * Destroy a program analysis.
    */
   ~brw_analysis()
   {
      delete p;
   }

   /**
    * Obtain the result of a program analysis.  This gives a
    * guaranteed up-to-date result, the analysis pass will be
    * rerun implicitly if it has become stale.
    */
   T &
   require()
   {
      if (p)
         assert(p->validate(c));
      else
         p = new T(c);

      return *p;
   }

   const T &
   require() const
   {
      return const_cast<brw_analysis<T, C> *>(this)->require();
   }

   /**
    * Report that dependencies of the analysis pass may have changed
    * since the last calculation and the cached analysis result may
    * have to be discarded.
    */
   void
   invalidate(brw::analysis_dependency_class c)
   {
      if (p && (c & p->dependency_class())) {
         delete p;
         p = NULL;
      }
   }

private:
   const C *c;
   T *p;
};

#endif