DAG: Avoid OOB when legalizing vector indexing

If a vector index is out of bounds, the result is supposed to be
undefined but is not undefined behavior. Change the legalization
for indexing the vector on the stack so that an out of bounds
index does not create an out of bounds memory access.

llvm-svn: 291604

1 files changed, 44 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index 591a37d600c..690f0d2c808 100644
--- a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -3706,7 +3706,7 @@ SDValue TargetLowering::expandUnalignedStore(StoreSDNode *ST,
   return Result;
 }
 
-SDValue 
+SDValue
 TargetLowering::IncrementMemoryAddress(SDValue Addr, SDValue Mask,
                                        const SDLoc &DL, EVT DataVT,
                                        SelectionDAG &DAG,
@@ -3738,6 +3738,49 @@ TargetLowering::IncrementMemoryAddress(SDValue Addr, SDValue Mask,
   return DAG.getNode(ISD::ADD, DL, AddrVT, Addr, Increment);
 }
 
+static SDValue clampDynamicVectorIndex(SelectionDAG &DAG,
+                                       SDValue Idx,
+                                       EVT VecVT,
+                                       const SDLoc &dl) {
+  if (isa<ConstantSDNode>(Idx))
+    return Idx;
+
+  EVT IdxVT = Idx.getValueType();
+  unsigned NElts = VecVT.getVectorNumElements();
+  if (isPowerOf2_32(NElts)) {
+    APInt Imm = APInt::getLowBitsSet(IdxVT.getSizeInBits(),
+                                     Log2_32(NElts));
+    return DAG.getNode(ISD::AND, dl, IdxVT, Idx,
+                       DAG.getConstant(Imm, dl, IdxVT));
+  }
+
+  return DAG.getNode(ISD::UMIN, dl, IdxVT, Idx,
+                     DAG.getConstant(NElts - 1, dl, IdxVT));
+}
+
+SDValue TargetLowering::getVectorElementPointer(SelectionDAG &DAG,
+                                                SDValue VecPtr, EVT VecVT,
+                                                SDValue Index) const {
+  SDLoc dl(Index);
+  // Make sure the index type is big enough to compute in.
+  Index = DAG.getZExtOrTrunc(Index, dl, getPointerTy(DAG.getDataLayout()));
+
+  EVT EltVT = VecVT.getVectorElementType();
+
+  // Calculate the element offset and add it to the pointer.
+  unsigned EltSize = EltVT.getSizeInBits() / 8; // FIXME: should be ABI size.
+  assert(EltSize * 8 == EltVT.getSizeInBits() &&
+         "Converting bits to bytes lost precision");
+
+  Index = clampDynamicVectorIndex(DAG, Index, VecVT, dl);
+
+  EVT IdxVT = Index.getValueType();
+
+  Index = DAG.getNode(ISD::MUL, dl, IdxVT, Index,
+                      DAG.getConstant(EltSize, dl, IdxVT));
+  return DAG.getNode(ISD::ADD, dl, IdxVT, Index, VecPtr);
+}
+
 //===----------------------------------------------------------------------===//
 // Implementation of Emulated TLS Model
 //===----------------------------------------------------------------------===//