Fix UndefVarError in previously untested code path, fixes #292.

Author: chriselrod

src/codegen/loopstartstopmanager.jl

@@ -366,7 +366,7 @@ function cse_constant_offsets!(
               Expr(:call, GlobalRef(Base,:(-)), gespsymbol, name(op2))
             end
             gespsymbol = gensym!(ls, "#gespsym#")
-            push!(q.args, Expr(:(=), gespsymbol, subexpr))
+            pushpreamble!(ls, Expr(:(=), gespsymbol, subexpr))
             ind = maybeloopvaluename(op1)
             substitute_ops_all!(ls, i, ii, indop, op1, allarrayrefs, array_refs_with_same_name, arrayref_to_name_op_collection)
           else

test/copy.jl

@@ -266,5 +266,15 @@ using LoopVectorization, OffsetArrays, Test
         issue280!(dest2, src2)
         @test dest2 ≈ vcat(view(src,2,:)',view(src,1,:)')
       end
+
+      rng = 10:20
+      arr1 = zeros(30);
+      arr2 = zeros(30);
+      ifirst = 5
+      @turbo for i in rng
+        arr1[i-ifirst] += 1
+      end
+      @. arr2[rng-ifirst] += 1;
+      @test arr1 == arr2
     end
 end