From 83814325b45f9f53480f633d7d36ed005f9fa823 Mon Sep 17 00:00:00 2001
From: Nicholas Mazzuca <npmazzuca@gmail.com>
Date: Tue, 28 Apr 2015 18:20:30 -0700
Subject: [PATCH] Add intrinsics for unchecked division and modulo

The "unchecked_" div and rem functions will give UB in case of rhs == 0, or,
in the signed versions, lhs == INT::min and rhs == -1
---
 src/libcore/intrinsics.rs             | 17 +++++++++++++++++
 src/librustc_trans/trans/context.rs   |  1 +
 src/librustc_trans/trans/intrinsic.rs |  8 ++++++++
 src/librustc_typeck/check/mod.rs      |  5 +++++
 4 files changed, 31 insertions(+)

diff --git a/src/libcore/intrinsics.rs b/src/libcore/intrinsics.rs
index 8ed89adec5b6..c6bb1fb1cb16 100644
--- a/src/libcore/intrinsics.rs
+++ b/src/libcore/intrinsics.rs
@@ -576,3 +576,20 @@ extern "rust-intrinsic" {
     #[cfg(not(stage0))]
     pub fn discriminant_value<T>(v: &T) -> u64;
 }
+
+#[cfg(not(stage0))]
+extern "rust-intrinsic" {
+    /// Performs an unchecked signed division, which results in undefined behavior,
+    /// in cases where y == 0, or x == int::MIN and y == -1
+    pub fn unchecked_sdiv<T>(x: T, y: T) -> T;
+    /// Performs an unchecked unsigned division, which results in undefined behavior,
+    /// in cases where y == 0
+    pub fn unchecked_udiv<T>(x: T, y: T) -> T;
+
+    /// Returns the remainder of an unchecked signed division, which results in
+    /// undefined behavior, in cases where y == 0, or x == int::MIN and y == -1
+    pub fn unchecked_urem<T>(x: T, y: T) -> T;
+    /// Returns the remainder of an unchecked signed division, which results in
+    /// undefined behavior, in cases where y == 0
+    pub fn unchecked_srem<T>(x: T, y: T) -> T;
+}
diff --git a/src/librustc_trans/trans/context.rs b/src/librustc_trans/trans/context.rs
index 1506e5b26698..41ef566f2fd7 100644
--- a/src/librustc_trans/trans/context.rs
+++ b/src/librustc_trans/trans/context.rs
@@ -735,6 +735,7 @@ impl<'b, 'tcx> CrateContext<'b, 'tcx> {
     }
 }
 
+/// Declare any llvm intrinsics that you might need
 fn declare_intrinsic(ccx: &CrateContext, key: & &'static str) -> Option<ValueRef> {
     macro_rules! ifn {
         ($name:expr, fn() -> $ret:expr) => (
diff --git a/src/librustc_trans/trans/intrinsic.rs b/src/librustc_trans/trans/intrinsic.rs
index 6bfa80f9c40b..ed0beee20b04 100644
--- a/src/librustc_trans/trans/intrinsic.rs
+++ b/src/librustc_trans/trans/intrinsic.rs
@@ -144,6 +144,9 @@ pub fn check_intrinsics(ccx: &CrateContext) {
     ccx.sess().abort_if_errors();
 }
 
+/// Remember to add all intrinsics here, in librustc_typeck/check/mod.rs,
+/// and in libcore/intrinsics.rs; if you need access to any llvm intrinsics,
+/// add them to librustc_trans/trans/context.rs
 pub fn trans_intrinsic_call<'a, 'blk, 'tcx>(mut bcx: Block<'blk, 'tcx>,
                                             node: ast::NodeId,
                                             callee_ty: Ty<'tcx>,
@@ -676,6 +679,11 @@ pub fn trans_intrinsic_call<'a, 'blk, 'tcx>(mut bcx: Block<'blk, 'tcx>,
                                     llargs[1],
                                     call_debug_location),
 
+        (_, "unchecked_udiv") => UDiv(bcx, llargs[0], llargs[1], call_debug_location),
+        (_, "unchecked_sdiv") => SDiv(bcx, llargs[0], llargs[1], call_debug_location),
+        (_, "unchecked_urem") => URem(bcx, llargs[0], llargs[1], call_debug_location),
+        (_, "unchecked_srem") => SRem(bcx, llargs[0], llargs[1], call_debug_location),
+
         (_, "overflowing_add") => Add(bcx, llargs[0], llargs[1], call_debug_location),
         (_, "overflowing_sub") => Sub(bcx, llargs[0], llargs[1], call_debug_location),
         (_, "overflowing_mul") => Mul(bcx, llargs[0], llargs[1], call_debug_location),
diff --git a/src/librustc_typeck/check/mod.rs b/src/librustc_typeck/check/mod.rs
index f9c78cd36e6a..c28548321402 100644
--- a/src/librustc_typeck/check/mod.rs
+++ b/src/librustc_typeck/check/mod.rs
@@ -4882,6 +4882,8 @@ pub fn check_bounds_are_used<'a, 'tcx>(ccx: &CrateCtxt<'a, 'tcx>,
     }
 }
 
+/// Remember to add all intrinsics here, in librustc_trans/trans/intrinsic.rs,
+/// and in libcore/intrinsics.rs
 pub fn check_intrinsic_type(ccx: &CrateCtxt, it: &ast::ForeignItem) {
     fn param<'a, 'tcx>(ccx: &CrateCtxt<'a, 'tcx>, n: u32) -> Ty<'tcx> {
         let name = token::intern(&format!("P{}", n));
@@ -5119,6 +5121,9 @@ pub fn check_intrinsic_type(ccx: &CrateCtxt, it: &ast::ForeignItem) {
                 (0, vec!(tcx.types.u64, tcx.types.u64),
                 ty::mk_tup(tcx, vec!(tcx.types.u64, tcx.types.bool))),
 
+            "unchecked_udiv" | "unchecked_sdiv" | "unchecked_urem" | "unchecked_srem" =>
+                (1, vec![param(ccx, 0), param(ccx, 0)], param(ccx, 0)),
+
             "overflowing_add" | "overflowing_sub" | "overflowing_mul" =>
                 (1, vec![param(ccx, 0), param(ccx, 0)], param(ccx, 0)),