diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -4094,7 +4094,7 @@
     if (!IsScalableVec && Ty->isSized()) {
       Value *P;
       uint64_t C;
-      uint64_t TyAllocSize = Q.DL.getTypeAllocSize(Ty);
+      uint64_t TyAllocSize = Q.DL.getTypeAllocSize(Ty).getFixedSize();
       // getelementptr P, N -> P if P points to a type of zero size.
       if (TyAllocSize == 0 && Ops[0]->getType() == GEPTy)
         return Ops[0];
@@ -4139,12 +4139,15 @@
     }
   }
 
-  if (!IsScalableVec && Q.DL.getTypeAllocSize(LastType) == 1 &&
+  if (!IsScalableVec && Q.DL.getTypeAllocSize(LastType).getFixedSize() == 1 &&
       all_of(Ops.slice(1).drop_back(1),
              [](Value *Idx) { return match(Idx, m_Zero()); })) {
     unsigned IdxWidth =
         Q.DL.getIndexSizeInBits(Ops[0]->getType()->getPointerAddressSpace());
-    if (Q.DL.getTypeSizeInBits(Ops.back()->getType()) == IdxWidth) {
+    // Skip if offset type size is not a compile-time constant.
+    TypeSize OffsetTypeSize = Q.DL.getTypeSizeInBits(Ops.back()->getType());
+    if (!OffsetTypeSize.isScalable() &&
+        OffsetTypeSize.getFixedSize() == IdxWidth) {
       APInt BasePtrOffset(IdxWidth, 0);
       Value *StrippedBasePtr =
           Ops[0]->stripAndAccumulateInBoundsConstantOffsets(Q.DL,