[LV] Add test case where variable induction step needs truncating.

Author: fhahn

llvm/test/Transforms/LoopVectorize/cast-induction.ll

@@ -73,3 +73,43 @@ loop:
 exit:
   ret void
 }
+
+
+define void @cast_variable_step(i64 %step) {
+; VF4-LABEL: @cast_variable_step(
+; VF4-LABEL: vector.body:
+; VF4: [[VEC_IND:%.+]] = phi <4 x i32>
+; VF4: store <4 x i32> [[VEC_IND]]
+; VF4: middle.block:
+;
+; IC2-LABEL: @cast_variable_step(
+; IC2-LABEL: vector.body:
+; IC2-NEXT:   [[INDEX:%.+]] = phi i64 [ 0, %vector.ph ]
+; IC2-NEXT:   [[MUL:%.+]] = mul i64 %index, %step
+; IC2-NEXT:   [[OFFSET_IDX:%.+]] = add i64 10, [[MUL]]
+; IC2-NEXT:   [[TRUNC_OFF:%.+]] = trunc i64 [[OFFSET_IDX]] to i32
+; IC2-NEXT:   [[TRUNC_STEP:%.+]] = trunc i64 %step to i32
+; IC2-NEXT:   [[STEP0:%.+]] = mul i32 0, [[TRUNC_STEP]]
+; IC2-NEXT:   [[T0:%.+]] = add i32 [[TRUNC_OFF]], [[STEP0]]
+; IC2-NEXT:   [[STEP1:%.+]] = mul i32 1, [[TRUNC_STEP]]
+; IC2-NEXT:   [[T1:%.+]] = add i32 [[TRUNC_OFF]], [[STEP1]]
+; IC2:        store i32 [[T0]],
+; IC2-NEXT:   store i32 [[T1]],
+;
+entry:
+  br label %loop
+
+loop:
+  %iv = phi i64 [ 0, %entry ], [ %iv.next, %loop ]
+  %iv.2 = phi i64 [ 10, %entry ], [ %iv.2.next, %loop ]
+  %gep = getelementptr inbounds [2048 x i32], ptr @a, i64 0, i64 %iv
+  %iv.2.trunc = trunc i64 %iv.2 to i32
+  store i32 %iv.2.trunc, ptr %gep, align 4
+  %iv.next = add i64 %iv, 1
+  %iv.2.next = add i64 %iv.2, %step
+  %exitcond = icmp eq i64 %iv.next, 1024
+  br i1 %exitcond, label %exit, label %loop
+
+exit:
+  ret void
+}