IR: Change the gep_type_iterator API to avoid always exposing the "current" type.

Instead, expose whether the current type is an array or a struct, if an array
what the upper bound is, and if a struct the struct type itself. This is
in preparation for a later change which will make PointerType derive from
Type rather than SequentialType.

Differential Revision: https://reviews.llvm.org/D26594

llvm-svn: 288458
diff --git a/llvm/lib/CodeGen/CodeGenPrepare.cpp b/llvm/lib/CodeGen/CodeGenPrepare.cpp
index 60ac557..0ae57ce 100644
--- a/llvm/lib/CodeGen/CodeGenPrepare.cpp
+++ b/llvm/lib/CodeGen/CodeGenPrepare.cpp
@@ -3261,7 +3261,7 @@
     int64_t ConstantOffset = 0;
     gep_type_iterator GTI = gep_type_begin(AddrInst);
     for (unsigned i = 1, e = AddrInst->getNumOperands(); i != e; ++i, ++GTI) {
-      if (StructType *STy = dyn_cast<StructType>(*GTI)) {
+      if (StructType *STy = GTI.getStructTypeOrNull()) {
         const StructLayout *SL = DL.getStructLayout(STy);
         unsigned Idx =
           cast<ConstantInt>(AddrInst->getOperand(i))->getZExtValue();
diff --git a/llvm/lib/CodeGen/SelectionDAG/FastISel.cpp b/llvm/lib/CodeGen/SelectionDAG/FastISel.cpp
index 7bc0c9d..e2f33bb 100644
--- a/llvm/lib/CodeGen/SelectionDAG/FastISel.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/FastISel.cpp
@@ -488,7 +488,7 @@
   for (gep_type_iterator GTI = gep_type_begin(I), E = gep_type_end(I);
        GTI != E; ++GTI) {
     const Value *Idx = GTI.getOperand();
-    if (auto *StTy = dyn_cast<StructType>(*GTI)) {
+    if (StructType *StTy = GTI.getStructTypeOrNull()) {
       uint64_t Field = cast<ConstantInt>(Idx)->getZExtValue();
       if (Field) {
         // N = N + Offset
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 01c7c14..09f2bbc 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -3274,7 +3274,7 @@
   for (gep_type_iterator GTI = gep_type_begin(&I), E = gep_type_end(&I);
        GTI != E; ++GTI) {
     const Value *Idx = GTI.getOperand();
-    if (StructType *StTy = dyn_cast<StructType>(*GTI)) {
+    if (StructType *StTy = GTI.getStructTypeOrNull()) {
       unsigned Field = cast<Constant>(Idx)->getUniqueInteger().getZExtValue();
       if (Field) {
         // N = N + Offset