diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -2343,7 +2343,12 @@
     // The bitcasts will either all exist or all not exist. The builder will
     // not create unnecessary casts if the types already match.
     Type *SelTy = A->getType();
-    if (auto *VecTy = dyn_cast<VectorType>(Cond->getType())) {
+    auto *VecTy = dyn_cast<VectorType>(Cond->getType());
+    // Check whether we have to cast.
+    if (VecTy && VecTy != C->getType()) {
+      // If we do have to cast, we must avoid scalable vectors here.
+      if (VecTy->getElementCount().isScalable())
+        return nullptr;
       unsigned Elts = VecTy->getElementCount().getKnownMinValue();
       Type *EltTy = Builder.getIntNTy(SelTy->getPrimitiveSizeInBits() / Elts);
       SelTy = VectorType::get(EltTy, VecTy->getElementCount());
diff --git a/llvm/test/Transforms/InstCombine/logical-select.ll b/llvm/test/Transforms/InstCombine/logical-select.ll
--- a/llvm/test/Transforms/InstCombine/logical-select.ll
+++ b/llvm/test/Transforms/InstCombine/logical-select.ll
@@ -471,6 +471,18 @@
   ret <4 x i1> %or
 }
 
+define <vscale x 1 x i1> @vec_of_bools_scalable(<vscale x 1 x i1> %a, <vscale x 1 x i1> %c, <vscale x 1 x i1> %d) {
+; CHECK-LABEL: @vec_of_bools_scalable(
+; CHECK-NEXT:    [[TMP1:%.*]] = select <vscale x 1 x i1> [[A:%.*]], <vscale x 1 x i1> [[C:%.*]], <vscale x 1 x i1> [[D:%.*]]
+; CHECK-NEXT:    ret <vscale x 1 x i1> [[TMP1]]
+;
+  %b = xor <vscale x 1 x i1> %a, shufflevector (<vscale x 1 x i1> insertelement (<vscale x 1 x i1> poison, i1 true, i32 0), <vscale x 1 x i1> poison, <vscale x 1 x i32> zeroinitializer)
+  %t11 = and <vscale x 1 x i1> %a, %c
+  %t12 = and <vscale x 1 x i1> %b, %d
+  %r = or <vscale x 1 x i1> %t11, %t12
+  ret <vscale x 1 x i1> %r
+}
+
 define i4 @vec_of_casted_bools(i4 %a, i4 %b, <4 x i1> %c) {
 ; CHECK-LABEL: @vec_of_casted_bools(
 ; CHECK-NEXT:    [[TMP1:%.*]] = bitcast i4 [[B:%.*]] to <4 x i1>
@@ -488,6 +500,31 @@
   ret i4 %or
 }
 
+; Negative test - we can't create the correct scalable vector casts
+
+define <vscale x 1 x i64> @vec_of_casted_bools_scalable(<vscale x 1 x i64> %a, <vscale x 1 x i64> %b, <vscale x 8 x i1> %cond) {
+; CHECK-LABEL: @vec_of_casted_bools_scalable(
+; CHECK-NEXT:    [[SCOND:%.*]] = sext <vscale x 8 x i1> [[COND:%.*]] to <vscale x 8 x i8>
+; CHECK-NEXT:    [[NOTCOND:%.*]] = xor <vscale x 8 x i1> [[COND]], shufflevector (<vscale x 8 x i1> insertelement (<vscale x 8 x i1> poison, i1 true, i32 0), <vscale x 8 x i1> poison, <vscale x 8 x i32> zeroinitializer)
+; CHECK-NEXT:    [[SNOTCOND:%.*]] = sext <vscale x 8 x i1> [[NOTCOND]] to <vscale x 8 x i8>
+; CHECK-NEXT:    [[BC1:%.*]] = bitcast <vscale x 8 x i8> [[SCOND]] to <vscale x 1 x i64>
+; CHECK-NEXT:    [[BC2:%.*]] = bitcast <vscale x 8 x i8> [[SNOTCOND]] to <vscale x 1 x i64>
+; CHECK-NEXT:    [[AND1:%.*]] = and <vscale x 1 x i64> [[BC1]], [[A:%.*]]
+; CHECK-NEXT:    [[AND2:%.*]] = and <vscale x 1 x i64> [[BC2]], [[B:%.*]]
+; CHECK-NEXT:    [[OR:%.*]] = or <vscale x 1 x i64> [[AND1]], [[AND2]]
+; CHECK-NEXT:    ret <vscale x 1 x i64> [[OR]]
+;
+  %scond = sext <vscale x 8 x i1> %cond to <vscale x 8 x i8>
+  %notcond = xor <vscale x 8 x i1> %cond, shufflevector (<vscale x 8 x i1> insertelement (<vscale x 8 x i1> poison, i1 true, i32 0), <vscale x 8 x i1> poison, <vscale x 8 x i32> zeroinitializer)
+  %snotcond = sext <vscale x 8 x i1> %notcond to <vscale x 8 x i8>
+  %bc1 = bitcast <vscale x 8 x i8> %scond to <vscale x 1 x i64>
+  %bc2 = bitcast <vscale x 8 x i8> %snotcond to <vscale x 1 x i64>
+  %and1 = and <vscale x 1 x i64> %a, %bc1
+  %and2 = and <vscale x 1 x i64> %bc2, %b
+  %or = or <vscale x 1 x i64> %and1, %and2
+  ret <vscale x 1 x i64> %or
+}
+
 ; Inverted 'and' constants mean this is a select which is canonicalized to a shuffle.
 
 define <4 x i32> @vec_sel_consts(<4 x i32> %a, <4 x i32> %b) {