diff --git a/llvm/lib/Analysis/ConstantFolding.cpp b/llvm/lib/Analysis/ConstantFolding.cpp
--- a/llvm/lib/Analysis/ConstantFolding.cpp
+++ b/llvm/lib/Analysis/ConstantFolding.cpp
@@ -352,9 +352,9 @@
                                          const DataLayout &DL) {
   do {
     Type *SrcTy = C->getType();
-    uint64_t DestSize = DL.getTypeSizeInBits(DestTy);
-    uint64_t SrcSize = DL.getTypeSizeInBits(SrcTy);
-    if (SrcSize < DestSize)
+    TypeSize DestSize = DL.getTypeSizeInBits(DestTy);
+    TypeSize SrcSize = DL.getTypeSizeInBits(SrcTy);
+    if (TypeSize::isKnownLT(SrcSize, DestSize))
       return nullptr;
 
     // Catch the obvious splat cases (since all-zeros can coerce non-integral
diff --git a/llvm/test/Transforms/InstCombine/vscale_load_bitcast.ll b/llvm/test/Transforms/InstCombine/vscale_load_bitcast.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/vscale_load_bitcast.ll
@@ -0,0 +1,13 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -instcombine -S -verify | FileCheck %s
+
+define <8 x i8> @constprop_load_bitcast() {
+; CHECK-LABEL: @constprop_load_bitcast(
+; CHECK-NEXT:    ret <8 x i8> zeroinitializer
+;
+  %stack_var = alloca <vscale x 16 x i1>, align 16
+  store <vscale x 16 x i1> zeroinitializer, <vscale x 16 x i1>* %stack_var, align 16
+  %cast_to_fixed = bitcast <vscale x 16 x i1>* %stack_var to <8 x i8>*
+  %a = load <8 x i8>, <8 x i8>* %cast_to_fixed, align 16
+  ret <8 x i8> %a
+}