Descriptor object used to manage abstract frame references

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@5166 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/llvm/CodeGen/MachineFrameInfo.h b/include/llvm/CodeGen/MachineFrameInfo.h
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+//===-- CodeGen/FunctionFrameInfo.h - Abstract Stack Frame Rep --*- C++ -*-===//
+// 
+// The FunctionFrameInfo class represents an abstract stack frame until
+// prolog/epilog code is inserted.  This class is key to allowing stack frame
+// representation optimizations, such as frame pointer elimination.  It also
+// allows more mundane (but still important) optimizations, such as reordering
+// of abstract objects on the stack frame.
+//
+// To support this, the class assigns unique integer identifiers to stack
+// objects requested clients.  These identifiers are negative integers for fixed
+// stack objects (such as arguments passed on the stack) or positive for objects
+// that may be reordered.  Instructions which refer to stack objects use a
+// special MO_FrameIndex operand to represent these frame indexes.
+//
+// Because this class keeps track of all references to the stack frame, it knows
+// when a variable sized object is allocated on the stack.  This is the sole
+// condition which prevents frame pointer elimination, which is an important
+// optimization on register-poor architectures.  Because original variable sized
+// alloca's in the source program are the only source of variable sized stack
+// objects, it is safe to decide whether there will be any variable sized
+// objects before all stack objects are known (for example, register allocator
+// spill code never needs variable sized objects).
+//
+// When prolog/epilog code emission is performed, the final stack frame is built
+// and the machine instructions are modified to refer to the actual stack
+// offsets of the object, eliminating all MO_FrameIndex operands from the
+// program.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CODEGEN_FUNCTIONFRAMEINFO_H
+#define LLVM_CODEGEN_FUNCTIONFRAMEINFO_H
+
+class FunctionFrameInfo {
+
+  // StackObject - Represent a single object allocated on the stack.
+  struct StackObject {
+    // The size of this object on the stack. 0 means a variable sized object
+    unsigned Size;
+
+    // Alignment - The required alignment of this stack slot.
+    unsigned Alignment;
+
+    // SPOffset - The offset of this object from the stack pointer on entry to
+    // the function.  This field has no meaning for a variable sized element.
+    int SPOffset;
+
+    StackObject(unsigned Sz, unsigned Al, int SP)
+      : Size(Sz), Alignment(Al), SPOffset(SP) {}
+  };
+
+  /// Objects - The list of stack objects allocated...
+  ///
+  std::vector<StackObject> Objects;
+
+  /// NumFixedObjects - This contains the number of fixed objects contained on
+  /// the stack.  Because fixed objects are stored at a negative index in the
+  /// Objects list, this is also the index to the 0th object in the list.
+  ///
+  unsigned NumFixedObjects;
+
+  /// HasVarSizedObjects - This boolean keeps track of whether any variable
+  /// sized objects have been allocated yet.
+  ///
+  bool HasVarSizedObjects;
+
+  /// StackSize - The prolog/epilog code inserter calculates the final stack
+  /// offsets for all of the fixed size objects, updating the Objects list
+  /// above.  It then updates StackSize to contain the number of bytes that need
+  /// to be allocated on entry to the function.
+  ///
+  unsigned StackSize;
+
+  /// HasCalls - Set to true if this function has any function calls.  This is
+  /// only valid during and after prolog/epilog code insertion.
+  bool HasCalls;
+
+  /// MaxCallFrameSize - This contains the size of the largest call frame if the
+  /// target uses frame setup/destroy pseudo instructions (as defined in the
+  /// TargetFrameInfo class).  This information is important for frame pointer
+  /// elimination.  If is only valid during and after prolog/epilog code
+  /// insertion.
+  ///
+  unsigned MaxCallFrameSize;
+public:
+  FunctionFrameInfo() {
+    NumFixedObjects = StackSize = 0;
+    HasVarSizedObjects = false;
+    HasCalls = false;
+    MaxCallFrameSize = 0;
+  }
+
+  /// hasStackObjects - Return true if there are any stack objects in this
+  /// function.
+  ///
+  bool hasStackObjects() const { return !Objects.empty(); }
+
+  /// hasVarSizedObjects - This method may be called any time after instruction
+  /// selection is complete to determine if the stack frame for this function
+  /// contains any variable sized objects.
+  ///
+  bool hasVarSizedObjects() const { return HasVarSizedObjects; }
+
+  /// getObjectIndexBegin - Return the minimum frame object index...
+  ///
+  int getObjectIndexBegin() const { return -NumFixedObjects; }
+
+  /// getObjectIndexEnd - Return one past the maximum frame object index...
+  ///
+  int getObjectIndexEnd() const { return Objects.size()-NumFixedObjects; }
+
+  /// getObjectSize - Return the size of the specified object
+  ///
+  int getObjectSize(int ObjectIdx) const {
+    assert(ObjectIdx+NumFixedObjects < Objects.size() && "Invalid Object Idx!");
+    return Objects[ObjectIdx+NumFixedObjects].Size;
+  }
+
+  /// getObjectAlignment - Return the alignment of the specified stack object...
+  int getObjectAlignment(int ObjectIdx) const {
+    assert(ObjectIdx+NumFixedObjects < Objects.size() && "Invalid Object Idx!");
+    return Objects[ObjectIdx+NumFixedObjects].Alignment;
+  }
+
+  /// getObjectOffset - Return the assigned stack offset of the specified object
+  /// from the incoming stack pointer.
+  ///
+  int getObjectOffset(int ObjectIdx) const {
+    assert(ObjectIdx+NumFixedObjects < Objects.size() && "Invalid Object Idx!");
+    return Objects[ObjectIdx+NumFixedObjects].SPOffset;
+  }
+
+  /// setObjectOffset - Set the stack frame offset of the specified object.  The
+  /// offset is relative to the stack pointer on entry to the function.
+  ///
+  void setObjectOffset(int ObjectIdx, int SPOffset) {
+    assert(ObjectIdx+NumFixedObjects < Objects.size() && "Invalid Object Idx!");
+    Objects[ObjectIdx+NumFixedObjects].SPOffset = SPOffset;
+  }
+
+  /// getStackSize - Return the number of bytes that must be allocated to hold
+  /// all of the fixed size frame objects.  This is only valid after
+  /// Prolog/Epilog code insertion has finalized the stack frame layout.
+  ///
+  unsigned getStackSize() const { return StackSize; }
+
+  /// setStackSize - Set the size of the stack...
+  ///
+  void setStackSize(unsigned Size) { StackSize = Size; }
+
+  /// hasCalls - Return true if the current function has no function calls.
+  /// This is only valid during or after prolog/epilog code emission.
+  ///
+  bool hasCalls() const { return HasCalls; }
+  void setHasCalls(bool V) { HasCalls = V; }
+  
+  /// getMaxCallFrameSize - Return the maximum size of a call frame that must be
+  /// allocated for an outgoing function call.  This is only available if
+  /// CallFrameSetup/Destroy pseudo instructions are used by the target, and
+  /// then only during or after prolog/epilog code insertion.
+  ///
+  unsigned getMaxCallFrameSize() const { return MaxCallFrameSize; }
+  void setMaxCallFrameSize(unsigned S) { MaxCallFrameSize = S; }
+
+  /// CreateFixedObject - Create a new object at a fixed location on the stack.
+  /// All fixed objects should be created before other objects are created for
+  /// efficiency.  This returns an index with a negative value.
+  ///
+  int CreateFixedObject(unsigned Size, int SPOffset) {
+    assert(Size != 0 && "Cannot allocate zero size fixed stack objects!");
+    Objects.insert(Objects.begin(), StackObject(Size, 1, SPOffset));
+    return -++NumFixedObjects;
+  }
+  
+  /// CreateStackObject - Create a new statically sized stack object, returning
+  /// a postive identifier to represent it.
+  ///
+  int CreateStackObject(unsigned Size, unsigned Alignment) {
+    assert(Size != 0 && "Cannot allocate zero size stack objects!");
+    Objects.push_back(StackObject(Size, Alignment, -1));
+    return Objects.size()-NumFixedObjects-1;
+  }
+
+  /// CreateVariableSizedObject - Notify the FunctionFrameInfo object that a
+  /// variable sized object has been created.  This must be created whenever a
+  /// variable sized object is created, whether or not the index returned is
+  /// actually used.
+  ///
+  int CreateVariableSizedObject() {
+    HasVarSizedObjects = true;
+    Objects.push_back(StackObject(0, 1, -1));
+    return Objects.size()-NumFixedObjects-1;
+  }
+
+  /// print - Used by the MachineFunction printer to print information about
+  /// stack objects.  Implemented in MachineFunction.cpp
+  ///
+  void print(std::ostream &OS) const;
+
+  /// dump - Call print(std::cerr) to be called from the debugger.
+  void dump() const;
+};
+
+#endif