---

yaml
---
r: 216372
b: refs/heads/stable
c: 36dccec
h: refs/heads/master
v: v3

Author: dotdash

[refs]

@@ -29,5 +29,5 @@ refs/heads/tmp: 378a370ff2057afeb1eae86eb6e78c476866a4a6
 refs/tags/1.0.0-alpha.2: 4c705f6bc559886632d3871b04f58aab093bfa2f
 refs/tags/homu-tmp: a5286998df566e736b32f6795bfc3803bdaf453d
 refs/tags/1.0.0-beta: 8cbb92b53468ee2b0c2d3eeb8567005953d40828
-refs/heads/stable: 8f991d1fc27a176254ebfe99ed7e5a339cb9c7e2
+refs/heads/stable: 36dccec2f39c7e1da7f056ea421ad5256df3fb0b
 refs/tags/1.0.0: 55bd4f8ff2b323f317ae89e254ce87162d52a375

branches/stable/src/libcore/num/mod.rs

@@ -745,7 +745,20 @@ macro_rules! uint_impl {
         #[stable(feature = "rust1", since = "1.0.0")]
         #[inline]
         pub fn trailing_zeros(self) -> u32 {
-            unsafe { $cttz(self as $ActualT) as u32 }
+            // As of LLVM 3.6 the codegen for the zero-safe cttz8 intrinsic
+            // emits two conditional moves on x86_64. By promoting the value to
+            // u16 and setting bit 8, we get better code without any conditional
+            // operations.
+            // FIXME: There's a LLVM patch (http://reviews.llvm.org/D9284)
+            // pending, remove this workaround once LLVM generates better code
+            // for cttz8.
+            unsafe {
+                if $BITS == 8 {
+                    intrinsics::cttz16(self as u16 | 0x100) as u32
+                } else {
+                    $cttz(self as $ActualT) as u32
+                }
+            }
         }
 
         /// Shifts the bits to the left by a specified amount, `n`,