Subzero: Improve handling of alloca instructions of constant size.

src/IceInst.h

 //===- subzero/src/IceInst.h - High-level instructions ----------*- C++ -*-===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 228 matching lines @@
   InstAlloca &operator=(const InstAlloca &) = delete;
 
 public:
   static InstAlloca *create(Cfg *Func, Operand *ByteCount,
                             uint32_t AlignInBytes, Variable *Dest) {
     return new (Func->allocate<InstAlloca>())
         InstAlloca(Func, ByteCount, AlignInBytes, Dest);
   }
   uint32_t getAlignInBytes() const { return AlignInBytes; }
   Operand *getSizeInBytes() const { return getSrc(0); }
+  bool getKnownFrameOffset() const { return KnownFrameOffset; }
+  void setKnownFrameOffset() { KnownFrameOffset = true; }
   void dump(const Cfg *Func) const override;
   static bool classof(const Inst *Inst) { return Inst->getKind() == Alloca; }
 
 private:
   InstAlloca(Cfg *Func, Operand *ByteCount, uint32_t AlignInBytes,
              Variable *Dest);
 
   const uint32_t AlignInBytes;
+  bool KnownFrameOffset = false;
 };
 
 /// Binary arithmetic instruction. The source operands are captured in getSrc(0)
 /// and getSrc(1).
 class InstArithmetic : public InstHighLevel {
   InstArithmetic() = delete;
   InstArithmetic(const InstArithmetic &) = delete;
   InstArithmetic &operator=(const InstArithmetic &) = delete;
 
 public:
@@ skipping 702 matching lines @@
   static void noteHead(Ice::Inst *, Ice::Inst *) {}
   void deleteNode(Ice::Inst *) {}
 
 private:
   mutable ilist_half_node<Ice::Inst> Sentinel;
 };
 
 } // end of namespace llvm
 
 #endif // SUBZERO_SRC_ICEINST_H