Hoist the GEP constant address offset computation to a common home on

the GEP instruction class.

This is part of the continued refactoring and cleaning of the
infrastructure used by SROA. This particular operation is also done in
a few other places which I'll try to refactor to share this
implementation.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@169852 91177308-0d34-0410-b5e6-96231b3b80d8

lib/VMCore/Instructions.cpp

@@ -15,6 +15,7 @@
 #include "llvm/Instructions.h"
 #include "LLVMContextImpl.h"
 #include "llvm/Constants.h"
+#include "llvm/DataLayout.h"
 #include "llvm/DerivedTypes.h"
 #include "llvm/Function.h"
 #include "llvm/Module.h"
@@ -22,6 +23,7 @@
 #include "llvm/Support/CallSite.h"
 #include "llvm/Support/ConstantRange.h"
 #include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/GetElementPtrTypeIterator.h"
 #include "llvm/Support/MathExtras.h"
 using namespace llvm;
 
@@ -1423,6 +1425,37 @@ bool GetElementPtrInst::isInBounds() const {
   return cast<GEPOperator>(this)->isInBounds();
 }
 
+bool GetElementPtrInst::accumulateConstantOffset(const DataLayout &DL,
+                                                 APInt &Offset) const {
+  assert(Offset.getBitWidth() ==
+         DL.getPointerSizeInBits(getPointerAddressSpace()) &&
+         "The offset must have exactly as many bits as our pointer.");
+
+  for (gep_type_iterator GTI = gep_type_begin(this), GTE = gep_type_end(this);
+       GTI != GTE; ++GTI) {
+    ConstantInt *OpC = dyn_cast<ConstantInt>(GTI.getOperand());
+    if (!OpC)
+      return false;
+    if (OpC->isZero())
+      continue;
+
+    // Handle a struct index, which adds its field offset to the pointer.
+    if (StructType *STy = dyn_cast<StructType>(*GTI)) {
+      unsigned ElementIdx = OpC->getZExtValue();
+      const StructLayout *SL = DL.getStructLayout(STy);
+      Offset += APInt(Offset.getBitWidth(),
+                      SL->getElementOffset(ElementIdx));
+      continue;
+    }
+
+    // For array or vector indices, scale the index by the size of the type.
+    APInt Index = OpC->getValue().sextOrTrunc(Offset.getBitWidth());
+    Offset += Index * APInt(Offset.getBitWidth(),
+                            DL.getTypeAllocSize(GTI.getIndexedType()));
+  }
+  return true;
+}
+
 //===----------------------------------------------------------------------===//
 //                           ExtractElementInst Implementation
 //===----------------------------------------------------------------------===//