Emit range metadata on calls returning scalars (fixes rust-lang#50157)

src/librustc_trans/abi.rs

@@ -1042,7 +1042,7 @@ impl<'a, 'tcx> FnType<'tcx> {
         }
     }
 
-    pub fn apply_attrs_callsite(&self, callsite: ValueRef) {
+    pub fn apply_attrs_callsite(&self, bx: &Builder<'a, 'tcx>, callsite: ValueRef) {
         let mut i = 0;
         let mut apply = |attrs: &ArgAttributes| {
             attrs.apply_callsite(llvm::AttributePlace::Argument(i), callsite);
@@ -1055,6 +1055,27 @@ impl<'a, 'tcx> FnType<'tcx> {
             PassMode::Indirect(ref attrs) => apply(attrs),
             _ => {}
         }
+        if let layout::Abi::Scalar(ref scalar) = self.ret.layout.abi {
+            let (min, max) = (scalar.valid_range.start, scalar.valid_range.end);
+            let max_next = max.wrapping_add(1);
+            let bits = scalar.value.size(bx.cx).bits();
+            assert!(bits <= 128);
+            let mask = !0u128 >> (128 - bits);
+            // For a (max) value of -1, max will be `-1 as usize`, which overflows.
+            // However, that is fine here (it would still represent the full range),
+            // i.e., if the range is everything.  The lo==hi case would be
+            // rejected by the LLVM verifier (it would mean either an
+            // empty set, which is impossible, or the entire range of the
+            // type, which is pointless).
+            match scalar.value {
+                layout::Int(..) if !scalar.is_bool() && max_next & mask != min & mask => {
+                    // llvm::ConstantRange can deal with ranges that wrap around,
+                    // so an overflow on (max + 1) is fine.
+                    bx.range_metadata(callsite, min..max_next);
+                }
+                _ => {}
+            }
+        }
         for arg in &self.args {
             if arg.pad.is_some() {
                 apply(&ArgAttributes::new());

src/librustc_trans/mir/block.rs

@@ -127,7 +127,7 @@ impl<'a, 'tcx> FunctionCx<'a, 'tcx> {
                                            ret_bx,
                                            llblock(this, cleanup),
                                            cleanup_bundle);
-                fn_ty.apply_attrs_callsite(invokeret);
+                fn_ty.apply_attrs_callsite(&bx, invokeret);
 
                 if let Some((ret_dest, target)) = destination {
                     let ret_bx = this.build_block(target);
@@ -136,7 +136,7 @@ impl<'a, 'tcx> FunctionCx<'a, 'tcx> {
                 }
             } else {
                 let llret = bx.call(fn_ptr, &llargs, cleanup_bundle);
-                fn_ty.apply_attrs_callsite(llret);
+                fn_ty.apply_attrs_callsite(&bx, llret);
                 if this.mir[bb].is_cleanup {
                     // Cleanup is always the cold path. Don't inline
                     // drop glue. Also, when there is a deeply-nested

src/test/codegen/call-metadata.rs

@@ -0,0 +1,27 @@
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Checks that range metadata gets emitted on calls to functions returning a
+// scalar value.
+
+// compile-flags: -C no-prepopulate-passes
+
+#![crate_type = "lib"]
+
+pub fn test() {
+    // CHECK: call i8 @some_true(), !range [[R0:![0-9]+]]
+    // CHECK: [[R0]] = !{i8 0, i8 3}
+    some_true();
+}
+
+#[no_mangle]
+fn some_true() -> Option<bool> {
+    Some(true)
+}