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

include/llvm/Analysis/PtrUseVisitor.h

@@ -29,7 +29,6 @@
 #include "llvm/InstVisitor.h"
 #include "llvm/IntrinsicInst.h"
 #include "llvm/Support/Compiler.h"
-#include "llvm/Support/GetElementPtrTypeIterator.h"
 
 namespace llvm {
 

include/llvm/Instructions.h

@@ -29,9 +29,10 @@
 
 namespace llvm {
 
+class APInt;
 class ConstantInt;
 class ConstantRange;
-class APInt;
+class DataLayout;
 class LLVMContext;
 
 enum AtomicOrdering {
@@ -850,6 +851,16 @@ public:
   /// isInBounds - Determine whether the GEP has the inbounds flag.
   bool isInBounds() const;
 
+  /// \brief Accumulate the constant address offset of this GEP if possible.
+  ///
+  /// This routine accepts an APInt into which it will accumulate the constant
+  /// offset of this GEP if the GEP is in fact constant. If the GEP is not
+  /// all-constant, it returns false and the value of the offset APInt is
+  /// undefined (it is *not* preserved!). The APInt passed into this routine
+  /// must be at least as wide as the IntPtr type for the address space of
+  /// the base GEP pointer.
+  bool accumulateConstantOffset(const DataLayout &DL, APInt &Offset) const;
+
   // Methods for support type inquiry through isa, cast, and dyn_cast:
   static inline bool classof(const Instruction *I) {
     return (I->getOpcode() == Instruction::GetElementPtr);

lib/Analysis/PtrUseVisitor.cpp

@@ -32,27 +32,5 @@ bool detail::PtrUseVisitorBase::adjustOffsetForGEP(GetElementPtrInst &GEPI) {
   if (!IsOffsetKnown)
     return false;
 
-  for (gep_type_iterator GTI = gep_type_begin(GEPI), GTE = gep_type_end(GEPI);
-       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;
+  return GEPI.accumulateConstantOffset(DL, Offset);
 }

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
 //===----------------------------------------------------------------------===//