I've stumbled across a bug with the AOT compiler. Compiling the following code causes an "Instruction does not dominate all uses!" error from LLVM: --*begin code*-- def test_method(a_hash) a_hash.each{|k,v| puts "Key: #{k} and Value: #{v}"} end test_method({:hello => 'world'}) --*end code*-- I haven't had time to add this to test_vm, but I did narrow down the issue to this region of the generated llvm assembly: --*begin code*-- rescue_save_vars: ; preds = %MainBlock %7 = call i8* @llvm.eh.exception() ; <i8*> [#uses=2] %8 = call i64 (i8*, i8*, ...)* @llvm.eh.selector.i64(i8* %7, i8* bitcast (i8* ()* @__gxx_personality_v0 to i8*), i8* null) ; <i64> [#uses=0] %9 = call i8* @__cxa_begin_catch(i8* %7) ; <i8*> [#uses=0] %10 = load i8** %1 ; <i8*> [#uses=2] %11 = icmp eq i8* %10, null ; <i1> [#uses=1] br i1 %11, label %merge, label %not_null normal: ; preds = %MainBlock %12 = load i64* @6 ; <i64> [#uses=2] %13 = load i8** %1 ; <i8*> [#uses=1] call void (i8*, i32, ...)* @rb_vm_keep_vars(i8* %13, i32 1, i64 %12, i64* %0) ret i64 %6 not_null: ; preds = %rescue_save_vars call void (i8*, i32, ...)* @rb_vm_keep_vars(i8* %10, i32 1, i64 %12, i64* %0) br label %merge --*end code*-- Specifically, the issue is that "not_null" can be accessed directly from "rescue_save_vars" leaving %12 undefined. I've attached the related files. Cheers, Josh