Speed up reading/writing slices with #[inline]

When built with `rustc -O`:

before:

test bench_read_slice  ... bench:        68 ns/iter (+/- 56)
test bench_read_vec    ... bench:        78 ns/iter (+/- 21)
test bench_write_slice ... bench:       133 ns/iter (+/- 46)
test bench_write_vec   ... bench:       308 ns/iter (+/- 69)

after:

test bench_read_slice  ... bench:        32 ns/iter (+/- 10)
test bench_read_vec    ... bench:        32 ns/iter (+/- 8)
test bench_write_slice ... bench:        53 ns/iter (+/- 12)
test bench_write_vec   ... bench:       247 ns/iter (+/- 172)

src/libstd/io/impls.rs

@@ -24,38 +24,58 @@
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a, R: Read + ?Sized> Read for &'a mut R {
+    #[inline]
     fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
         (**self).read(buf)
     }
+
+    #[inline]
     fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize> {
         (**self).read_to_end(buf)
     }
+
+    #[inline]
     fn read_to_string(&mut self, buf: &mut String) -> io::Result<usize> {
         (**self).read_to_string(buf)
     }
 }
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a, W: Write + ?Sized> Write for &'a mut W {
+    #[inline]
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> { (**self).write(buf) }
+
+    #[inline]
     fn flush(&mut self) -> io::Result<()> { (**self).flush() }
+
+    #[inline]
     fn write_all(&mut self, buf: &[u8]) -> io::Result<()> {
         (**self).write_all(buf)
     }
+
+    #[inline]
     fn write_fmt(&mut self, fmt: fmt::Arguments) -> io::Result<()> {
         (**self).write_fmt(fmt)
     }
 }
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a, S: Seek + ?Sized> Seek for &'a mut S {
+    #[inline]
     fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> { (**self).seek(pos) }
 }
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a, B: BufRead + ?Sized> BufRead for &'a mut B {
+    #[inline]
     fn fill_buf(&mut self) -> io::Result<&[u8]> { (**self).fill_buf() }
+
+    #[inline]
     fn consume(&mut self, amt: usize) { (**self).consume(amt) }
+
+    #[inline]
     fn read_until(&mut self, byte: u8, buf: &mut Vec<u8>) -> io::Result<usize> {
         (**self).read_until(byte, buf)
     }
+
+    #[inline]
     fn read_line(&mut self, buf: &mut String) -> io::Result<usize> {
         (**self).read_line(buf)
     }
@@ -63,38 +83,58 @@ fn read_line(&mut self, buf: &mut String) -> io::Result<usize> {
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<R: Read + ?Sized> Read for Box<R> {
+    #[inline]
     fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
         (**self).read(buf)
     }
+
+    #[inline]
     fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize> {
         (**self).read_to_end(buf)
     }
+
+    #[inline]
     fn read_to_string(&mut self, buf: &mut String) -> io::Result<usize> {
         (**self).read_to_string(buf)
     }
 }
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<W: Write + ?Sized> Write for Box<W> {
+    #[inline]
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> { (**self).write(buf) }
+
+    #[inline]
     fn flush(&mut self) -> io::Result<()> { (**self).flush() }
+
+    #[inline]
     fn write_all(&mut self, buf: &[u8]) -> io::Result<()> {
         (**self).write_all(buf)
     }
+
+    #[inline]
     fn write_fmt(&mut self, fmt: fmt::Arguments) -> io::Result<()> {
         (**self).write_fmt(fmt)
     }
 }
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<S: Seek + ?Sized> Seek for Box<S> {
+    #[inline]
     fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> { (**self).seek(pos) }
 }
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<B: BufRead + ?Sized> BufRead for Box<B> {
+    #[inline]
     fn fill_buf(&mut self) -> io::Result<&[u8]> { (**self).fill_buf() }
+
+    #[inline]
     fn consume(&mut self, amt: usize) { (**self).consume(amt) }
+
+    #[inline]
     fn read_until(&mut self, byte: u8, buf: &mut Vec<u8>) -> io::Result<usize> {
         (**self).read_until(byte, buf)
     }
+
+    #[inline]
     fn read_line(&mut self, buf: &mut String) -> io::Result<usize> {
         (**self).read_line(buf)
     }
@@ -105,6 +145,7 @@ fn read_line(&mut self, buf: &mut String) -> io::Result<usize> {
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a> Read for &'a [u8] {
+    #[inline]
     fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
         let amt = cmp::min(buf.len(), self.len());
         let (a, b) = self.split_at(amt);
@@ -116,12 +157,16 @@ fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a> BufRead for &'a [u8] {
+    #[inline]
     fn fill_buf(&mut self) -> io::Result<&[u8]> { Ok(*self) }
+
+    #[inline]
     fn consume(&mut self, amt: usize) { *self = &self[amt..]; }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a> Write for &'a mut [u8] {
+    #[inline]
     fn write(&mut self, data: &[u8]) -> io::Result<usize> {
         let amt = cmp::min(data.len(), self.len());
         let (a, b) = mem::replace(self, &mut []).split_at_mut(amt);
@@ -130,6 +175,7 @@ fn write(&mut self, data: &[u8]) -> io::Result<usize> {
         Ok(amt)
     }
 
+    #[inline]
     fn write_all(&mut self, data: &[u8]) -> io::Result<()> {
         if try!(self.write(data)) == data.len() {
             Ok(())
@@ -138,20 +184,87 @@ fn write_all(&mut self, data: &[u8]) -> io::Result<()> {
         }
     }
 
+    #[inline]
     fn flush(&mut self) -> io::Result<()> { Ok(()) }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl Write for Vec<u8> {
+    #[inline]
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
         self.push_all(buf);
         Ok(buf.len())
     }
 
+    #[inline]
     fn write_all(&mut self, buf: &[u8]) -> io::Result<()> {
         self.push_all(buf);
         Ok(())
     }
 
+    #[inline]
     fn flush(&mut self) -> io::Result<()> { Ok(()) }
 }
+
+#[cfg(test)]
+mod tests {
+    use io::prelude::*;
+    use vec::Vec;
+    use test;
+
+    #[bench]
+    fn bench_read_slice(b: &mut test::Bencher) {
+        let buf = [5; 1024];
+        let mut dst = [0; 128];
+
+        b.iter(|| {
+            let mut rd = &buf[..];
+            for _ in (0 .. 8) {
+                let _ = rd.read(&mut dst);
+                test::black_box(&dst);
+            }
+        })
+    }
+
+    #[bench]
+    fn bench_write_slice(b: &mut test::Bencher) {
+        let mut buf = [0; 1024];
+        let src = [5; 128];
+
+        b.iter(|| {
+            let mut wr = &mut buf[..];
+            for _ in (0 .. 8) {
+                let _ = wr.write_all(&src);
+                test::black_box(&wr);
+            }
+        })
+    }
+
+    #[bench]
+    fn bench_read_vec(b: &mut test::Bencher) {
+        let buf = vec![5; 1024];
+        let mut dst = [0; 128];
+
+        b.iter(|| {
+            let mut rd = &buf[..];
+            for _ in (0 .. 8) {
+                let _ = rd.read(&mut dst);
+                test::black_box(&dst);
+            }
+        })
+    }
+
+    #[bench]
+    fn bench_write_vec(b: &mut test::Bencher) {
+        let mut buf = Vec::with_capacity(1024);
+        let src = [5; 128];
+
+        b.iter(|| {
+            let mut wr = &mut buf[..];
+            for _ in (0 .. 8) {
+                let _ = wr.write_all(&src);
+                test::black_box(&wr);
+            }
+        })
+    }
+}