Shrink the size of AllocationInst by using its SubclassData

field to store the alignment value instead of haing a
separate field.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@48727 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 13 insertions, 10 deletions

diff --git a/include/llvm/Instructions.h b/include/llvm/Instructions.h
index c80154c..2e234bd 100644
--- a/include/llvm/Instructions.h
+++ b/include/llvm/Instructions.h
@@ -21,6 +21,7 @@
 #include "llvm/InstrTypes.h"
 #include "llvm/DerivedTypes.h"
 #include "llvm/ParameterAttributes.h"
+#include "llvm/Support/MathExtras.h"
 
 namespace llvm {
 
@@ -39,7 +40,6 @@ class APInt;
 /// AllocaInst.
 ///
 class AllocationInst : public UnaryInstruction {
-  unsigned Alignment;
 protected:
   AllocationInst(const Type *Ty, Value *ArraySize, unsigned iTy, unsigned Align,
                  const std::string &Name = "", Instruction *InsertBefore = 0);
@@ -74,11 +74,8 @@ public:
   /// getAlignment - Return the alignment of the memory that is being allocated
   /// by the instruction.
   ///
-  unsigned getAlignment() const { return Alignment; }
-  void setAlignment(unsigned Align) {
-    assert((Align & (Align-1)) == 0 && "Alignment is not a power of 2!");
-    Alignment = Align;
-  }
+  unsigned getAlignment() const { return (1u << SubclassData) >> 1; }
+  void setAlignment(unsigned Align);
 
   virtual Instruction *clone() const = 0;
 
diff --git a/lib/VMCore/Instructions.cpp b/lib/VMCore/Instructions.cpp
index df5a2fc..33ab1c6 100644
--- a/lib/VMCore/Instructions.cpp
+++ b/lib/VMCore/Instructions.cpp
@@ -677,8 +677,8 @@ AllocationInst::AllocationInst(const Type *Ty, Value *ArraySize, unsigned iTy,
                                unsigned Align, const std::string &Name,
                                Instruction *InsertBefore)
   : UnaryInstruction(PointerType::getUnqual(Ty), iTy, getAISize(ArraySize),
-                     InsertBefore), Alignment(Align) {
-  assert((Align & (Align-1)) == 0 && "Alignment is not a power of 2!");
+                     InsertBefore) {
+  setAlignment(Align);
   assert(Ty != Type::VoidTy && "Cannot allocate void!");
   setName(Name);
 }
@@ -687,8 +687,8 @@ AllocationInst::AllocationInst(const Type *Ty, Value *ArraySize, unsigned iTy,
                                unsigned Align, const std::string &Name,
                                BasicBlock *InsertAtEnd)
   : UnaryInstruction(PointerType::getUnqual(Ty), iTy, getAISize(ArraySize),
-                     InsertAtEnd), Alignment(Align) {
-  assert((Align & (Align-1)) == 0 && "Alignment is not a power of 2!");
+                     InsertAtEnd) {
+  setAlignment(Align);
   assert(Ty != Type::VoidTy && "Cannot allocate void!");
   setName(Name);
 }
@@ -697,6 +697,12 @@ AllocationInst::AllocationInst(const Type *Ty, Value *ArraySize, unsigned iTy,
 AllocationInst::~AllocationInst() {
 }
 
+void AllocationInst::setAlignment(unsigned Align) {
+  assert((Align & (Align-1)) == 0 && "Alignment is not a power of 2!");
+  SubclassData = Log2_32(Align) + 1;
+  assert(getAlignment() == Align && "Alignment representation error!");
+}
+
 bool AllocationInst::isArrayAllocation() const {
   if (ConstantInt *CI = dyn_cast<ConstantInt>(getOperand(0)))
     return CI->getZExtValue() != 1;