From 750d912eb4e76885b633ae9f3ec7497fafff4d52 Mon Sep 17 00:00:00 2001
From: pca006132 <jl@m-labs.hk>
Date: Sat, 12 Feb 2022 21:19:11 +0800
Subject: [PATCH] nac3core: do list bound check and negative index handling

Raise error when index out of range. Note that we use llvm.expect to
tell the optimizer that we expect not to raise an exception, so the
normal path performance would be better. If this assumption is violated,
the exception overhead might be slightly larger, but the percentage
increase in overhead should not be high since exception unwinding is
already pretty slow.
---
 nac3core/src/codegen/expr.rs | 76 +++++++++++++++++++++++++++++++++++-
 1 file changed, 74 insertions(+), 2 deletions(-)

diff --git a/nac3core/src/codegen/expr.rs b/nac3core/src/codegen/expr.rs
index 0d704403..ff47a12b 100644
--- a/nac3core/src/codegen/expr.rs
+++ b/nac3core/src/codegen/expr.rs
@@ -3,6 +3,7 @@ use std::{collections::HashMap, convert::TryInto, iter::once};
 use crate::{
     codegen::{
         concrete_type::{ConcreteFuncArg, ConcreteTypeEnum, ConcreteTypeStore},
+        stmt::gen_raise,
         get_llvm_type,
         irrt::*,
         CodeGenContext, CodeGenTask,
@@ -283,6 +284,66 @@ impl<'ctx, 'a> CodeGenContext<'ctx, 'a> {
         self.gen_const(generator, &nac3parser::ast::Constant::Str(s.into()), self.primitives.str)
     }
 
+    pub fn raise_exn<G: CodeGenerator>(
+        &mut self,
+        generator: &mut G,
+        name: &str,
+        msg: BasicValueEnum<'ctx>,
+        params: [Option<IntValue<'ctx>>; 3],
+        loc: Location
+    ) {
+        let ty = self.get_llvm_type(generator, self.primitives.exception).into_pointer_type();
+        let zelf_ty: BasicTypeEnum = ty.get_element_type().into_struct_type().into();
+        let zelf = self.builder.build_alloca(zelf_ty, "alloca");
+        let int32 = self.ctx.i32_type();
+        let zero = int32.const_zero();
+        unsafe {
+            let id_ptr = self.builder.build_in_bounds_gep(zelf, &[zero, zero], "exn.id");
+            let id = self.resolver.get_string_id(name);
+            self.builder.build_store(id_ptr, int32.const_int(id as u64, false));
+            let ptr = self.builder.build_in_bounds_gep(
+                zelf, &[zero, int32.const_int(5, false)], "exn.msg");
+            self.builder.build_store(ptr, msg);
+            let i64_zero = self.ctx.i64_type().const_zero();
+            for (i, attr_ind) in [6, 7, 8].iter().enumerate() {
+                let ptr = self.builder.build_in_bounds_gep(
+                    zelf, &[zero, int32.const_int(*attr_ind, false)], "exn.param");
+                let val = params[i].map_or(i64_zero, |v| self.builder.build_int_s_extend(v, self.ctx.i64_type(), "sext"));
+                self.builder.build_store(ptr, val);
+            }
+        }
+        gen_raise(generator, self, Some(&zelf.into()), loc);
+    }
+
+    pub fn make_assert<G: CodeGenerator>(
+        &mut self,
+        generator: &mut G,
+        cond: IntValue<'ctx>,
+        err_name: &str,
+        err_msg: &str,
+        params: [Option<IntValue<'ctx>>; 3],
+        loc: Location
+    ) {
+        let i1 = self.ctx.bool_type();
+        let i1_true = i1.const_all_ones();
+        let expect_fun = self.module.get_function("llvm.expect.i1").unwrap_or_else(|| {
+            self.module.add_function("llvm.expect", i1.fn_type(&[i1.into(), i1.into()], false), None)
+        });
+        // we assume that the condition is most probably true, so the normal path is the most
+        // probable path
+        // even if this assumption is violated, it does not matter as exception unwinding is
+        // slow anyway...
+        let cond = self.builder.build_call(expect_fun, &[cond.into(), i1_true.into()], "expect")
+            .try_as_basic_value().left().unwrap().into_int_value();
+        let current_fun = self.builder.get_insert_block().unwrap().get_parent().unwrap();
+        let then_block = self.ctx.append_basic_block(current_fun, "succ");
+        let exn_block = self.ctx.append_basic_block(current_fun, "fail");
+        self.builder.build_conditional_branch(cond, then_block, exn_block);
+        self.builder.position_at_end(exn_block);
+        let err_msg = self.gen_string(generator, err_msg);
+        self.raise_exn(generator, err_name, err_msg, params, loc);
+        self.builder.position_at_end(then_block);
+    }
 }
 
 pub fn gen_constructor<'ctx, 'a, G: CodeGenerator>(
@@ -1125,12 +1186,23 @@ pub fn gen_expr<'ctx, 'a, G: CodeGenerator>(
                     );
                     res_array_ret.into()
                 } else {
-                    // TODO: bound check
-                    let index = generator
+                    let len = ctx.build_gep_and_load(v, &[zero, int32.const_int(1, false)])
+                        .into_int_value();
+                    let raw_index = generator
                         .gen_expr(ctx, slice)
                         .unwrap()
                         .to_basic_value_enum(ctx, generator)
                         .into_int_value();
+                    // handle negative index
+                    let is_negative = ctx.builder.build_int_compare(inkwell::IntPredicate::SLT, raw_index,
+                        generator.get_size_type(ctx.ctx).const_zero(), "is_neg");
+                    let adjusted = ctx.builder.build_int_add(raw_index, len, "adjusted");
+                    let index = ctx.builder.build_select(is_negative, adjusted, raw_index, "index").into_int_value();
+                    // unsigned less than is enough, because negative index after adjustment is
+                    // bigger than the length (for unsigned cmp)
+                    let bound_check = ctx.builder.build_int_compare(inkwell::IntPredicate::ULT, index, len, "inbound");
+                    ctx.make_assert(generator, bound_check, "0:IndexError", "index {0} out of bounds 0:{1}",
+                        [Some(raw_index), Some(len), None], expr.location);
                     ctx.build_gep_and_load(arr_ptr, &[index])
                 }
             } else if let TypeEnum::TTuple { .. } = &*ctx.unifier.get_ty(value.custom.unwrap()) {