Divide by zero during vectorize loops

[TH3CHARLie]

A repro:

#include "Halide.h"
using namespace Halide;

int main() {
    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, yi, yoo, yoi, yooo, yooi, yoio, yoii, yoio_x_f, v;
        local_sum.update(0).vectorize(y).split(y, yo, yi, 8, TailStrategy::Auto).split(yo, yoo, yoi, 8, TailStrategy::Auto).split(yoo, yooo, yooi, 8, TailStrategy::Auto);
        local_sum.update(0).rfactor(r.x, v);
        Pipeline p({blurry});
        Buffer<int> buf = p.realize({128, 128});
    }
    return 0;
}

Crash:

Program received signal SIGFPE, Arithmetic exception.
0x00007ffff0b64584 in Halide::Internal::(anonymous namespace)::VectorSubs::widen(Halide::Expr, int) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
(gdb) bt
#0  0x00007ffff0b64584 in Halide::Internal::(anonymous namespace)::VectorSubs::widen(Halide::Expr, int) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#1  0x00007ffff0b5ae6f in Halide::Internal::(anonymous namespace)::VectorSubs::visit(Halide::Internal::Mul const*) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#2  0x00007ffff073e713 in Halide::Internal::ExprNode<Halide::Internal::Mul>::mutate_expr(Halide::Internal::IRMutator*) const () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#3  0x00007ffff0749c8b in Halide::Internal::IRMutator::mutate(Halide::Expr const&) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#4  0x00007ffff0b5aa19 in Halide::Internal::(anonymous namespace)::VectorSubs::visit(Halide::Internal::Add const*) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#5  0x00007ffff073e6d3 in Halide::Internal::ExprNode<Halide::Internal::Add>::mutate_expr(Halide::Internal::IRMutator*) const () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#6  0x00007ffff0749c8b in Halide::Internal::IRMutator::mutate(Halide::Expr const&) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#7  0x00007ffff0b5ae19 in Halide::Internal::(anonymous namespace)::VectorSubs::visit(Halide::Internal::Mul const*) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#8  0x00007ffff073e713 in Halide::Internal::ExprNode<Halide::Internal::Mul>::mutate_expr(Halide::Internal::IRMutator*) const () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#9  0x00007ffff0749c8b in Halide::Internal::IRMutator::mutate(Halide::Expr const&) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#10 0x00007ffff0b5aa19 in Halide::Internal::(anonymous namespace)::VectorSubs::visit(Halide::Internal::Add const*) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#11 0x00007ffff073e6d3 in Halide::Internal::ExprNode<Halide::Internal::Add>::mutate_expr(Halide::Internal::IRMutator*) const () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#12 0x00007ffff0749c8b in Halide::Internal::IRMutator::mutate(Halide::Expr const&) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#13 0x00007ffff0b5fef6 in Halide::Internal::(anonymous namespace)::VectorSubs::visit(Halide::Internal::For const*) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#14 0x00007ffff073ea36 in Halide::Internal::StmtNode<Halide::Internal::For>::mutate_stmt(Halide::Internal::IRMutator*) const () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#15 0x00007ffff0749cbb in Halide::Internal::IRMutator::mutate(Halide::Internal::Stmt const&) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#16 0x00007ffff0b5ef2e in Halide::Internal::(anonymous namespace)::VectorSubs::visit(Halide::Internal::LetStmt const*) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#17 0x00007ffff073e9d6 in Halide::Internal::StmtNode<Halide::Internal::LetStmt>::mutate_stmt(Halide::Internal::IRMutator*) const () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#18 0x00007ffff0749cbb in Halide::Internal::IRMutator::mutate(Halide::Internal::Stmt const&) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#19 0x00007ffff0b5ffed in Halide::Internal::(anonymous namespace)::VectorSubs::visit(Halide::Internal::For const*) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#20 0x00007ffff073ea36 in Halide::Internal::StmtNode<Halide::Internal::For>::mutate_stmt(Halide::Internal::IRMutator*) const () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#21 0x00007ffff0749cbb in Halide::Internal::IRMutator::mutate(Halide::Internal::Stmt const&) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#22 0x00007ffff0b5ffed in Halide::Internal::(anonymous namespace)::VectorSubs::visit(Halide::Internal::For const*) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#23 0x00007ffff073ea36 in Halide::Internal::StmtNode<Halide::Internal::For>::mutate_stmt(Halide::Internal::IRMutator*) const () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#24 0x00007ffff0749cbb in Halide::Internal::IRMutator::mutate(Halide::Internal::Stmt const&) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#25 0x00007ffff074d19c in Halide::Internal::IRMutator::visit(Halide::Internal::Block const*) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#26 0x00007ffff073eaf6 in Halide::Internal::StmtNode<Halide::Internal::Block>::mutate_stmt(Halide::Internal::IRMutator*) const () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#27 0x00007ffff0749cbb in Halide::Internal::IRMutator::mutate(Halide::Internal::Stmt const&) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#28 0x00007ffff074c38c in Halide::Internal::IRMutator::visit(Halide::Internal::ProducerConsumer const*) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#29 0x00007ffff073ea16 in Halide::Internal::StmtNode<Halide::Internal::ProducerConsumer>::mutate_stmt(Halide::Internal::IRMutator*) const () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#30 0x00007ffff0749cbb in Halide::Internal::IRMutator::mutate(Halide::Internal::Stmt const&) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#31 0x00007ffff074d188 in Halide::Internal::IRMutator::visit(Halide::Internal::Block const*) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#32 0x00007ffff073eaf6 in Halide::Internal::StmtNode<Halide::Internal::Block>::mutate_stmt(Halide::Internal::IRMutator*) const () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#33 0x00007ffff0749cbb in Halide::Internal::IRMutator::mutate(Halide::Internal::Stmt const&) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#34 0x00007ffff0b61210 in Halide::Internal::(anonymous namespace)::VectorSubs::visit(Halide::Internal::Allocate const*) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#35 0x00007ffff073ea96 in Halide::Internal::StmtNode<Halide::Internal::Allocate>::mutate_stmt(Halide::Internal::IRMutator*) const () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#36 0x00007ffff0749cbb in Halide::Internal::IRMutator::mutate(Halide::Internal::Stmt const&) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#37 0x00007ffff0b5fbb3 in Halide::Internal::(anonymous namespace)::VectorSubs::visit(Halide::Internal::For const*) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#38 0x00007ffff073ea36 in Halide::Internal::StmtNode<Halide::Internal::For>::mutate_stmt(Halide::Internal::IRMutator*) const () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#39 0x00007ffff0749cbb in Halide::Internal::IRMutator::mutate(Halide::Internal::Stmt const&) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#40 0x00007ffff0b5ffed in Halide::Internal::(anonymous namespace)::VectorSubs::visit(Halide::Internal::For const*) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#41 0x00007ffff073ea36 in Halide::Internal::StmtNode<Halide::Internal::For>::mutate_stmt(Halide::Internal::IRMutator*) const () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#42 0x00007ffff0749cbb in Halide::Internal::IRMutator::mutate(Halide::Internal::Stmt const&) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#43 0x00007ffff0b5ffed in Halide::Internal::(anonymous namespace)::VectorSubs::visit(Halide::Internal::For const*) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#44 0x00007ffff073ea36 in Halide::Internal::StmtNode<Halide::Internal::For>::mutate_stmt(Halide::Internal::IRMutator*) const () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#45 0x00007ffff0749cbb in Halide::Internal::IRMutator::mutate(Halide::Internal::Stmt const&) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#46 0x00007ffff0b58cae in Halide::Internal::(anonymous namespace)::VectorizeLoops::visit(Halide::Internal::For const*) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#47 0x00007ffff073ea36 in Halide::Internal::StmtNode<Halide::Internal::For>::mutate_stmt(Halide::Internal::IRMutator*) const () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#48 0x00007ffff0749cbb in Halide::Internal::IRMutator::mutate(Halide::Internal::Stmt const&) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#49 0x00007ffff074d19c in Halide::Internal::IRMutator::visit(Halide::Internal::Block const*) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#50 0x00007ffff073eaf6 in Halide::Internal::StmtNode<Halide::Internal::Block>::mutate_stmt(Halide::Internal::IRMutator*) const () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#51 0x00007ffff0749cbb in Halide::Internal::IRMutator::mutate(Halide::Internal::Stmt const&) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#52 0x00007ffff074c38c in Halide::Internal::IRMutator::visit(Halide::Internal::ProducerConsumer const*) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#53 0x00007ffff073ea16 in Halide::Internal::StmtNode<Halide::Internal::ProducerConsumer>::mutate_stmt(Halide::Internal::IRMutator*) const () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#54 0x00007ffff0749cbb in Halide::Internal::IRMutator::mutate(Halide::Internal::Stmt const&) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#55 0x00007ffff074d188 in Halide::Internal::IRMutator::visit(Halide::Internal::Block const*) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#56 0x00007ffff073eaf6 in Halide::Internal::StmtNode<Halide::Internal::Block>::mutate_stmt(Halide::Internal::IRMutator*) const () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#57 0x00007ffff0749cbb in Halide::Internal::IRMutator::mutate(Halide::Internal::Stmt const&) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#58 0x00007ffff074caae in Halide::Internal::IRMutator::visit(Halide::Internal::Allocate const*) () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17
#59 0x00007ffff073ea96 in Halide::Internal::StmtNode<Halide::Internal::Allocate>::mutate_stmt(Halide::Internal::IRMutator*) const () from /home/xuanda/dev/Serializer/Halide-clean/build/src/libHalide.so.17

[abadams]

This schedule creates vectors with 262144 lanes, because there are 6 nested for loops, each vectorized by a factor of 8. We only support vectors with up to 65535 lanes, so this overflows somewhere and ends up creating a zero-lane vector and then modding by zero. I'll add an overflow check somewhere to make this an error instead of a compiler crash.