[opaque pointer type] Allow gep_type_iterator to work with the pointee type from the GEP instruction

The raw non-instruction/constant form of this is still relying on being
able to access the pointee type from a pointer type - those will be
cleaned up later. For now, just focus on the cases where the pointee
type is easily accessible.

llvm-svn: 237958

1 files changed, 30 insertions, 0 deletions

diff --git a/llvm/lib/IR/Constants.cpp b/llvm/lib/IR/Constants.cpp
index d35372a2f8e..3665d5abb41 100644
--- a/llvm/lib/IR/Constants.cpp
+++ b/llvm/lib/IR/Constants.cpp
@@ -3050,3 +3050,33 @@ Instruction *ConstantExpr::getAsInstruction() {
     return BO;
   }
 }
+
+bool GEPOperator::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;
+}