Subzero: Tweaks to reduce malloc use.

src/IceRegAlloc.h

 //===- subzero/src/IceRegAlloc.h - Linear-scan reg. allocation --*- C++ -*-===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 25 matching lines @@
   void scan(const SmallBitVector &RegMask, bool Randomized);
   // Returns the number of times some variable has been assigned a register but
   // later evicted because of a higher-priority allocation.  The idea is that we
   // can implement "second-chance bin-packing" by rerunning register allocation
   // until there are no more evictions.
   SizeT getNumEvictions() const { return Evicted.size(); }
   bool hasEvictions() const { return !Evicted.empty(); }
   void dump(Cfg *Func) const;
 
   // TODO(stichnot): Statically choose the size based on the target being
-  // compiled.
-  static constexpr size_t REGS_SIZE = 32;
+  // compiled.  For now, choose a value large enough to fit into the
+  // SmallVector's fixed portion, which is 32 for x86-32, 84 for x86-64, and 102
+  // for ARM32.
+  static constexpr size_t REGS_SIZE = 128;
 
 private:
   using OrderedRanges = CfgVector<Variable *>;
   using UnorderedRanges = CfgVector<Variable *>;
   using DefUseErrorList = llvm::SmallVector<SizeT, 10>;
 
   class IterationState {
     IterationState(const IterationState &) = delete;
     IterationState operator=(const IterationState &) = delete;
 
   public:
     IterationState() = default;
     Variable *Cur = nullptr;
     Variable *Prefer = nullptr;
     RegNumT PreferReg;
     bool AllowOverlap = false;
     SmallBitVector RegMask;
     SmallBitVector RegMaskUnfiltered;
     SmallBitVector Free;
     SmallBitVector FreeUnfiltered;
     SmallBitVector PrecoloredUnhandledMask; // Note: only used for dumping
     llvm::SmallVector<RegWeight, REGS_SIZE> Weights;

[John, 2016/03/09 23:15:41]

Perhaps change this to std::array?

[Jim Stichnoth, 2016/03/09 23:19:31]

I did try making that change, and also to the two other instances of
SmallVector.  This also required removing the resize() and reserve() calls, plus
do something special about the register randomization interface.  Then it failed
various tests so I decided to defer it until working on the cleaner solution.

   };
 
   bool livenessValidateIntervals(const DefUseErrorList &DefsWithoutUses,
                                  const DefUseErrorList &UsesBeforeDefs,
                                  const CfgVector<InstNumberT> &LRBegin,
                                  const CfgVector<InstNumberT> &LREnd) const;
   void initForGlobal();
   void initForInfOnly();
   void initForSecondChance();
   /// Move an item from the From set to the To set. From[Index] is pushed onto
@@ skipping 50 matching lines @@
   bool FindPreference = false;
   bool FindOverlap = false;
 
   const bool Verbose;
   const bool UseReserve;
 };
 
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICEREGALLOC_H