1 files changed, 15 insertions, 8 deletions
diff --git a/llvm/lib/Target/ARM/ARMISelDAGToDAG.cpp b/llvm/lib/Target/ARM/ARMISelDAGToDAG.cpp
index 127d86c9138..c9a88823f5e 100644
--- a/llvm/lib/Target/ARM/ARMISelDAGToDAG.cpp
+++ b/llvm/lib/Target/ARM/ARMISelDAGToDAG.cpp
@@ -1150,15 +1150,22 @@ bool ARMDAGToDAGISel::SelectThumbAddrModeSP(SDValue N,
     if (isScaledConstantInRange(N.getOperand(1), /*Scale=*/4, 0, 256, RHSC)) {
       Base = N.getOperand(0);
       int FI = cast<FrameIndexSDNode>(Base)->getIndex();
-      // For LHS+RHS to result in an offset that's a multiple of 4 the object
-      // indexed by the LHS must be 4-byte aligned.
+      // Make sure the offset is inside the object, or we might fail to
+      // allocate an emergency spill slot. (An out-of-range access is UB, but
+      // it could show up anyway.)
       MachineFrameInfo &MFI = MF->getFrameInfo();
-      if (MFI.getObjectAlignment(FI) < 4)
-        MFI.setObjectAlignment(FI, 4);
-      Base = CurDAG->getTargetFrameIndex(
-          FI, TLI->getPointerTy(CurDAG->getDataLayout()));
-      OffImm = CurDAG->getTargetConstant(RHSC, SDLoc(N), MVT::i32);
-      return true;
+      if (RHSC * 4 < MFI.getObjectSize(FI)) {
+        // For LHS+RHS to result in an offset that's a multiple of 4 the object
+        // indexed by the LHS must be 4-byte aligned.
+        if (!MFI.isFixedObjectIndex(FI) && MFI.getObjectAlignment(FI) < 4)
+          MFI.setObjectAlignment(FI, 4);
+        if (MFI.getObjectAlignment(FI) >= 4) {
+          Base = CurDAG->getTargetFrameIndex(
+              FI, TLI->getPointerTy(CurDAG->getDataLayout()));
+          OffImm = CurDAG->getTargetConstant(RHSC, SDLoc(N), MVT::i32);
+          return true;
+        }
+      }
     }
   }