Segfault when simplifing let exprs

[TH3CHARLie]

a simple repro:

    Func input("input");
    Func local_sum("local_sum");
    Func blurry("blurry");
    Var x("x"), y("y");
    input(x, y) = 2 * x + 5 * y;
    RDom r(-2, 5, -2, 5);
    local_sum(x, y) = 0;
    local_sum(x, y) += input(x + r.x, y + r.y);
    blurry(x, y) = cast<int32_t>(local_sum(x, y) / 25);

    Var yo("yo"), yi("yi"), yiyof("yiyof"), yiyofxf("yiyofxf");
    blurry.split(y, yo, yi, 4, TailStrategy::GuardWithIf).fuse(yi, yo, yiyof).parallel(yiyof).fuse(yiyof, x, yiyofxf);
    local_sum.split(y, yo, yi, 4, TailStrategy::PredicateStores);
    local_sum.update(0).unscheduled();
    Pipeline p({blurry});
    Buffer<int> buf = p.realize({32, 32});

backtrace:

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff091e4a6 in Halide::Internal::Stmt Halide::Internal::Simplify::simplify_let<Halide::Internal::LetStmt, Halide::Internal::Stmt>(Halide::Internal::LetStmt const*, Halide::Internal::Simplify::ExprInfo*)
    () from /home/xuanda/dev/Serializer/Halide/build-clean/src/libHalide.so.17
(gdb) bt
#0  0x00007ffff091e4a6 in Halide::Internal::Stmt Halide::Internal::Simplify::simplify_let<Halide::Internal::LetStmt, Halide::Internal::Stmt>(Halide::Internal::LetStmt const*, Halide::Internal::Simplify::ExprInfo*) () from /home/xuanda/dev/Serializer/Halide/build-clean/src/libHalide.so.17
#1  0x00007ffff091933b in Halide::Internal::Simplify::visit(Halide::Internal::LetStmt const*) () from /home/xuanda/dev/Serializer/Halide/build-clean/src/libHalide.so.17
#2  0x00007ffff08b31e4 in Halide::Internal::Stmt Halide::Internal::VariadicVisitor<Halide::Internal::Simplify, Halide::Expr, Halide::Internal::Stmt>::dispatch_stmt<>(Halide::Internal::BaseStmtNode const*) ()
   from /home/xuanda/dev/Serializer/Halide/build-clean/src/libHalide.so.17
#3  0x00007ffff09f526a in Halide::Internal::Simplify::visit(Halide::Internal::For const*) () from /home/xuanda/dev/Serializer/Halide/build-clean/src/libHalide.so.17
#4  0x00007ffff08b3202 in Halide::Internal::Stmt Halide::Internal::VariadicVisitor<Halide::Internal::Simplify, Halide::Expr, Halide::Internal::Stmt>::dispatch_stmt<>(Halide::Internal::BaseStmtNode const*) ()
   from /home/xuanda/dev/Serializer/Halide/build-clean/src/libHalide.so.17
#5  0x00007ffff09f77e0 in Halide::Internal::Simplify::visit(Halide::Internal::ProducerConsumer const*) () from /home/xuanda/dev/Serializer/Halide/build-clean/src/libHalide.so.17
#6  0x00007ffff08b31f8 in Halide::Internal::Stmt Halide::Internal::VariadicVisitor<Halide::Internal::Simplify, Halide::Expr, Halide::Internal::Stmt>::dispatch_stmt<>(Halide::Internal::BaseStmtNode const*) ()
   from /home/xuanda/dev/Serializer/Halide/build-clean/src/libHalide.so.17
#7  0x00007ffff09f7a08 in Halide::Internal::Simplify::visit(Halide::Internal::Block const*) () from /home/xuanda/dev/Serializer/Halide/build-clean/src/libHalide.so.17
#8  0x00007ffff08b3248 in Halide::Internal::Stmt Halide::Internal::VariadicVisitor<Halide::Internal::Simplify, Halide::Expr, Halide::Internal::Stmt>::dispatch_stmt<>(Halide::Internal::BaseStmtNode const*) ()
   from /home/xuanda/dev/Serializer/Halide/build-clean/src/libHalide.so.17
#9  0x00007ffff091e413 in Halide::Internal::Stmt Halide::Internal::Simplify::simplify_let<Halide::Internal::LetStmt, Halide::Internal::Stmt>(Halide::Internal::LetStmt const*, Halide::Internal::Simplify::ExprInfo*) () from /home/xuanda/dev/Serializer/Halide/build-clean/src/libHalide.so.17
#10 0x00007ffff091933b in Halide::Internal::Simplify::visit(Halide::Internal::LetStmt const*) () from /home/xuanda/dev/Serializer/Halide/build-clean/src/libHalide.so.17
#11 0x00007ffff08b31e4 in Halide::Internal::Stmt Halide::Internal::VariadicVisitor<Halide::Internal::Simplify, Halide::Expr, Halide::Internal::Stmt>::dispatch_stmt<>(Halide::Internal::BaseStmtNode const*) ()
   from /home/xuanda/dev/Serializer/Halide/build-clean/src/libHalide.so.17
#12 0x00007ffff09f7a08 in Halide::Internal::Simplify::visit(Halide::Internal::Block const*) () from /home/xuanda/dev/Serializer/Halide/build-clean/src/libHalide.so.17
#13 0x00007ffff08b3248 in Halide::Internal::Stmt Halide::Internal::VariadicVisitor<Halide::Internal::Simplify, Halide::Expr, Halide::Internal::Stmt>::dispatch_stmt<>(Halide::Internal::BaseStmtNode const*) ()
   from /home/xuanda/dev/Serializer/Halide/build-clean/src/libHalide.so.17
#14 0x00007ffff09f31c0 in Halide::Internal::Simplify::visit(Halide::Internal::IfThenElse const*) () from /home/xuanda/dev/Serializer/Halide/build-clean/src/libHalide.so.17
#15 0x00007ffff08b325f in Halide::Internal::Stmt Halide::Internal::VariadicVisitor<Halide::Internal::Simplify, Halide::Expr, Halide::Internal::Stmt>::dispatch_stmt<>(Halide::Internal::BaseStmtNode const*) ()
   from /home/xuanda/dev/Serializer/Halide/build-clean/src/libHalide.so.17
#16 0x00007ffff09f7da0 in Halide::Internal::Simplify::visit(Halide::Internal::Block const*) () from /home/xuanda/dev/Serializer/Halide/build-clean/src/libHalide.so.17
#17 0x00007ffff08b3248 in Halide::Internal::Stmt Halide::Internal::VariadicVisitor<Halide::Internal::Simplify, Halide::Expr, Halide::Internal::Stmt>::dispatch_stmt<>(Halide::Internal::BaseStmtNode const*) ()
   from /home/xuanda/dev/Serializer/Halide/build-clean/src/libHalide.so.17
#18 0x00007ffff091e413 in Halide::Internal::Stmt Halide::Internal::Simplify::simplify_let<Halide::Internal::LetStmt, Halide::Internal::Stmt>(Halide::Internal::LetStmt const*, Halide::Internal::Simplify::ExprInfo*) () from /home/xuanda/dev/Serializer/Halide/build-clean/src/libHalide.so.17
#19 0x00007ffff091933b in Halide::Internal::Simplify::visit(Halide::Internal::LetStmt const*) () from /home/xuanda/dev/Serializer/Halide/build-clean/src/libHalide.so.17
#20 0x00007ffff08b31e4 in Halide::Internal::Stmt Halide::Internal::VariadicVisitor<Halide::Internal::Simplify, Halide::Expr, Halide::Internal::Stmt>::dispatch_stmt<>(Halide::Internal::BaseStmtNode const*) ()
   from /home/xuanda/dev/Serializer/Halide/build-clean/src/libHalide.so.17
#21 0x00007ffff09f7a08 in Halide::Internal::Simplify::visit(Halide::Internal::Block const*) () from /home/xuanda/dev/Serializer/Halide/build-clean/src/libHalide.so.17
#22 0x00007ffff08b3248 in Halide::Internal::Stmt Halide::Internal::VariadicVisitor<Halide::Internal::Simplify, Halide::Expr, Halide::Internal::Stmt>::dispatch_stmt<>(Halide::Internal::BaseStmtNode const*) ()
   from /home/xuanda/dev/Serializer/Halide/build-clean/src/libHalide.so.17
#23 0x00007ffff08b0367 in Halide::Internal::simplify(Halide::Internal::Stmt const&, bool, Halide::Internal::Scope<Halide::Internal::Interval> const&, Halide::Internal::Scope<Halide::Internal::ModulusRemainder> const&) () from /home/xuanda/dev/Serializer/Halide/build-clean/src/libHalide.so.17
#24 0x00007ffff07aab42 in Halide::Internal::(anonymous namespace)::lower_impl(std::vector<Halide::Internal::Function, std::allocator<Halide::Internal::Function> > const&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, Halide::Target const&, std::vector<Halide::Argument, std::allocator<Halide::Argument> > const&, Halide::LinkageType, std::vector<Halide::Internal::Stmt, std::allocator<Halide::Internal::Stmt> > const&, bool, std::vector<Halide::Internal::IRMutator*, std::allocator<Halide::Internal::IRMutator*> > const&, Halide::Module&) ()
   from /home/xuanda/dev/Serializer/Halide/build-clean/src/libHalide.so.17
#25 0x00007ffff07a7efb in std::_Function_handler<void (), Halide::Internal::lower(std::vector<Halide::Internal::Function, std::allocator<Halide::Internal::Function> > const&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, Halide::Target const&, std::vector<Halide::Argument, std::allocator<Halide::Argument> > const&, Halide::LinkageType, std::vector<Halide::Internal::Stmt, std::allocator<Halide::Internal::Stmt> > const&, bool, std::vector<Halide::Internal::IRMutator*, std::allocator<Halide::Internal::IRMutator*> > const&)::$_0>::_M_invoke(std::_Any_data const&) ()
   from /home/xuanda/dev/Serializer/Halide/build-clean/src/libHalide.so.17