Auto merge of #37083 - nnethercote:uleb128, r=eddyb

Inline read_{un,}signed_leb128 and opaque::Decoder functions.

`read_unsigned_leb128` is hot within rustc because it's heavily used
during the reading of crate metadata. This commit tweaks its signature
(and that of `read_signed_leb128`, for consistency) so it can increment
the buffer index directly instead of maintaining its own copy, the
change in which is then used by the caller to advance the index.

This reduces the instruction count (as measured by Cachegrind) for some
benchmarks a bit, e.g. hyper-0.5.0 by 0.7%.

2 files changed, 18 insertions, 0 deletions

diff --git a/src/libserialize/leb128.rs b/src/libserialize/leb128.rs
index 0c5356c0222..8e8e03f1f8e 100644
--- a/src/libserialize/leb128.rs
+++ b/src/libserialize/leb128.rs
@@ -38,6 +38,7 @@ pub fn write_unsigned_leb128(out: &mut Vec<u8>, start_position: usize, mut value
     return position - start_position;
 }
 
+#[inline]
 pub fn read_unsigned_leb128(data: &[u8], start_position: usize) -> (u64, usize) {
     let mut result = 0;
     let mut shift = 0;
@@ -78,6 +79,7 @@ pub fn write_signed_leb128(out: &mut Vec<u8>, start_position: usize, mut value:
     return position - start_position;
 }
 
+#[inline]
 pub fn read_signed_leb128(data: &[u8], start_position: usize) -> (i64, usize) {
     let mut result = 0;
     let mut shift = 0;
diff --git a/src/libserialize/opaque.rs b/src/libserialize/opaque.rs
index a2c0ca95447..87b6ed2ed40 100644
--- a/src/libserialize/opaque.rs
+++ b/src/libserialize/opaque.rs
@@ -179,74 +179,90 @@ macro_rules! read_sleb128 {
 impl<'a> serialize::Decoder for Decoder<'a> {
     type Error = String;
 
+    #[inline]
     fn read_nil(&mut self) -> Result<(), Self::Error> {
         Ok(())
     }
 
+    #[inline]
     fn read_u64(&mut self) -> Result<u64, Self::Error> {
         read_uleb128!(self, u64)
     }
 
+    #[inline]
     fn read_u32(&mut self) -> Result<u32, Self::Error> {
         read_uleb128!(self, u32)
     }
 
+    #[inline]
     fn read_u16(&mut self) -> Result<u16, Self::Error> {
         read_uleb128!(self, u16)
     }
 
+    #[inline]
     fn read_u8(&mut self) -> Result<u8, Self::Error> {
         let value = self.data[self.position];
         self.position += 1;
         Ok(value)
     }
 
+    #[inline]
     fn read_usize(&mut self) -> Result<usize, Self::Error> {
         read_uleb128!(self, usize)
     }
 
+    #[inline]
     fn read_i64(&mut self) -> Result<i64, Self::Error> {
         read_sleb128!(self, i64)
     }
 
+    #[inline]
     fn read_i32(&mut self) -> Result<i32, Self::Error> {
         read_sleb128!(self, i32)
     }
 
+    #[inline]
     fn read_i16(&mut self) -> Result<i16, Self::Error> {
         read_sleb128!(self, i16)
     }
 
+    #[inline]
     fn read_i8(&mut self) -> Result<i8, Self::Error> {
         let as_u8 = self.data[self.position];
         self.position += 1;
         unsafe { Ok(::std::mem::transmute(as_u8)) }
     }
 
+    #[inline]
     fn read_isize(&mut self) -> Result<isize, Self::Error> {
         read_sleb128!(self, isize)
     }
 
+    #[inline]
     fn read_bool(&mut self) -> Result<bool, Self::Error> {
         let value = self.read_u8()?;
         Ok(value != 0)
     }
 
+    #[inline]
     fn read_f64(&mut self) -> Result<f64, Self::Error> {
         let bits = self.read_u64()?;
         Ok(unsafe { ::std::mem::transmute(bits) })
     }
 
+    #[inline]
     fn read_f32(&mut self) -> Result<f32, Self::Error> {
         let bits = self.read_u32()?;
         Ok(unsafe { ::std::mem::transmute(bits) })
     }
 
+    #[inline]
     fn read_char(&mut self) -> Result<char, Self::Error> {
         let bits = self.read_u32()?;
         Ok(::std::char::from_u32(bits).unwrap())
     }
 
+    #[inline]
     fn read_str(&mut self) -> Result<Cow<str>, Self::Error> {
         let len = self.read_usize()?;
         let s = ::std::str::from_utf8(&self.data[self.position..self.position + len]).unwrap();