---

yaml
---
r: 210069
b: refs/heads/try
c: 36dccec
h: refs/heads/master
i:
  210067: c872cf6
v: v3

Author: dotdash

[refs]

@@ -2,7 +2,7 @@
 refs/heads/master: 3e561f05c00cd180ec02db4ccab2840a4aba93d2
 refs/heads/snap-stage1: e33de59e47c5076a89eadeb38f4934f58a3618a6
 refs/heads/snap-stage3: ba0e1cd8147d452c356aacb29fb87568ca26f111
-refs/heads/try: 8f991d1fc27a176254ebfe99ed7e5a339cb9c7e2
+refs/heads/try: 36dccec2f39c7e1da7f056ea421ad5256df3fb0b
 refs/tags/release-0.1: 1f5c5126e96c79d22cb7862f75304136e204f105
 refs/heads/dist-snap: ba4081a5a8573875fed17545846f6f6902c8ba8d
 refs/tags/release-0.2: c870d2dffb391e14efb05aa27898f1f6333a9596

branches/try/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`,