mir: report when overflow checks would be missing cross-crate.

src/librustc_mir/build/expr/as_rvalue.rs

@@ -80,7 +80,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
             ExprKind::Unary { op, arg } => {
                 let arg = unpack!(block = this.as_operand(block, arg));
                 // Check for -MIN on signed integers
-                if op == UnOp::Neg && this.check_overflow() && expr.ty.is_signed() {
+                if op == UnOp::Neg && expr.ty.is_signed() && this.check_overflow() {
                     let bool_ty = this.hir.bool_ty();
 
                     let minval = this.minval_literal(expr_span, expr.ty);
@@ -247,7 +247,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
                            lhs: Operand<'tcx>, rhs: Operand<'tcx>) -> BlockAnd<Rvalue<'tcx>> {
         let scope_id = self.innermost_scope_id();
         let bool_ty = self.hir.bool_ty();
-        if self.check_overflow() && op.is_checkable() && ty.is_integral() {
+        if op.is_checkable() && ty.is_integral() && self.check_overflow() {
             let result_tup = self.hir.tcx().mk_tup(vec![ty, bool_ty]);
             let result_value = self.temp(result_tup);
 

src/librustc_mir/build/mod.rs

@@ -55,6 +55,8 @@ pub struct Builder<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
     cached_resume_block: Option<BasicBlock>,
     /// cached block with the RETURN terminator
     cached_return_block: Option<BasicBlock>,
+
+    has_warned_about_xcrate_overflows: bool
 }
 
 struct CFG<'tcx> {
@@ -273,7 +275,8 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
             var_indices: FnvHashMap(),
             unit_temp: None,
             cached_resume_block: None,
-            cached_return_block: None
+            cached_return_block: None,
+            has_warned_about_xcrate_overflows: false
         };
 
         assert_eq!(builder.cfg.start_new_block(), START_BLOCK);
@@ -379,9 +382,19 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
         }
     }
 
-    pub fn check_overflow(&self) -> bool {
-        self.hir.tcx().sess.opts.debugging_opts.force_overflow_checks.unwrap_or(
-            self.hir.tcx().sess.opts.debug_assertions)
+    pub fn check_overflow(&mut self) -> bool {
+        let check = self.hir.tcx().sess.opts.debugging_opts.force_overflow_checks
+         .unwrap_or(self.hir.tcx().sess.opts.debug_assertions);
+
+        if !check && self.hir.may_be_inlined_cross_crate() {
+            if !self.has_warned_about_xcrate_overflows {
+                self.hir.tcx().sess.span_warn(self.fn_span,
+                    "overflow checks would be missing when used from another crate");
+                self.has_warned_about_xcrate_overflows = true;
+            }
+        }
+
+        check
     }
 }
 

src/librustc_mir/hair/cx/mod.rs

@@ -17,32 +17,63 @@
 
 use hair::*;
 use rustc::mir::repr::*;
+use rustc::mir::transform::MirSource;
 
 use rustc::middle::const_val::ConstVal;
 use rustc_const_eval as const_eval;
 use rustc::hir::def_id::DefId;
+use rustc::hir::intravisit::FnKind;
+use rustc::hir::map::blocks::FnLikeNode;
 use rustc::infer::InferCtxt;
 use rustc::ty::subst::{Subst, Substs};
 use rustc::ty::{self, Ty, TyCtxt};
 use syntax::parse::token;
 use rustc::hir;
 use rustc_const_math::{ConstInt, ConstUsize};
+use syntax::attr;
 
 #[derive(Copy, Clone)]
 pub struct Cx<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
     tcx: TyCtxt<'a, 'gcx, 'tcx>,
     infcx: &'a InferCtxt<'a, 'gcx, 'tcx>,
-    constness: hir::Constness
+    constness: hir::Constness,
+
+    /// True if this MIR can get inlined in other crates.
+    inline: bool
 }
 
 impl<'a, 'gcx, 'tcx> Cx<'a, 'gcx, 'tcx> {
     pub fn new(infcx: &'a InferCtxt<'a, 'gcx, 'tcx>,
-               constness: hir::Constness)
+               src: MirSource)
                -> Cx<'a, 'gcx, 'tcx> {
+        let (constness, inline) = match src {
+            MirSource::Const(_) |
+            MirSource::Static(..) => (hir::Constness::Const, false),
+            MirSource::Fn(id) => {
+                let def_id = infcx.tcx.map.local_def_id(id);
+                let fn_like = FnLikeNode::from_node(infcx.tcx.map.get(id));
+                match fn_like.map(|f| f.kind()) {
+                    Some(FnKind::ItemFn(_, _, _, c, _, _, attrs)) => {
+                        let scheme = infcx.tcx.lookup_item_type(def_id);
+                        let any_types = !scheme.generics.types.is_empty();
+                        (c, any_types || attr::requests_inline(attrs))
+                    }
+                    Some(FnKind::Method(_, m, _, attrs)) => {
+                        let scheme = infcx.tcx.lookup_item_type(def_id);
+                        let any_types = !scheme.generics.types.is_empty();
+                        (m.constness, any_types || attr::requests_inline(attrs))
+                    }
+                    _ => (hir::Constness::NotConst, true)
+                }
+            }
+            MirSource::Promoted(..) => bug!()
+        };
+
         Cx {
             tcx: infcx.tcx,
             infcx: infcx,
             constness: constness,
+            inline: inline
         }
     }
 }
@@ -154,6 +185,10 @@ impl<'a, 'gcx, 'tcx> Cx<'a, 'gcx, 'tcx> {
     pub fn tcx(&self) -> TyCtxt<'a, 'gcx, 'tcx> {
         self.tcx
     }
+
+    pub fn may_be_inlined_cross_crate(&self) -> bool {
+        self.inline
+    }
 }
 
 mod block;

src/librustc_mir/mir_map.rs

@@ -32,7 +32,6 @@ use rustc::ty::subst::Substs;
 use rustc::util::nodemap::NodeMap;
 use rustc::hir;
 use rustc::hir::intravisit::{self, FnKind, Visitor};
-use rustc::hir::map::blocks::FnLikeNode;
 use syntax::ast;
 use syntax::codemap::Span;
 
@@ -116,20 +115,7 @@ impl<'a, 'gcx, 'tcx> CxBuilder<'a, 'gcx, 'tcx> {
     {
         let src = self.src;
         let mir = self.infcx.enter(|infcx| {
-            let constness = match src {
-                MirSource::Const(_) |
-                MirSource::Static(..) => hir::Constness::Const,
-                MirSource::Fn(id) => {
-                    let fn_like = FnLikeNode::from_node(infcx.tcx.map.get(id));
-                    match fn_like.map(|f| f.kind()) {
-                        Some(FnKind::ItemFn(_, _, _, c, _, _, _)) => c,
-                        Some(FnKind::Method(_, m, _, _)) => m.constness,
-                        _ => hir::Constness::NotConst
-                    }
-                }
-                MirSource::Promoted(..) => bug!()
-            };
-            let (mut mir, scope_auxiliary) = f(Cx::new(&infcx, constness));
+            let (mut mir, scope_auxiliary) = f(Cx::new(&infcx, src));
 
             // Convert the Mir to global types.
             let mut globalizer = GlobalizeMir {