---

yaml
---
r: 123654
b: refs/heads/try
c: 31570cb
h: refs/heads/master
v: v3

Author: luqmana

[refs]

@@ -2,7 +2,7 @@
 refs/heads/master: da4e4e4e0a7778a85748aa4a303b13f603e96b4b
 refs/heads/snap-stage1: e33de59e47c5076a89eadeb38f4934f58a3618a6
 refs/heads/snap-stage3: 8ddd286ea4ba4384a0dc9eae393ed515460a986e
-refs/heads/try: e646188f66e40781131940d3b4d74a94cb2b10bf
+refs/heads/try: 31570cb22e8ab60233956368bad710f987a64b06
 refs/tags/release-0.1: 1f5c5126e96c79d22cb7862f75304136e204f105
 refs/heads/ndm: f3868061cd7988080c30d6d5bf352a5a5fe2460b
 refs/heads/try2: 147ecfdd8221e4a4d4e090486829a06da1e0ca3c

branches/try/src/libcollections/vec.rs

@@ -27,6 +27,10 @@ use {Collection, Mutable};
 use slice::{MutableOrdVector, MutableVectorAllocating, CloneableVector};
 use slice::{Items, MutItems};
 
+
+#[doc(hidden)]
+pub static PTR_MARKER: u8 = 0;
+
 /// An owned, growable vector.
 ///
 /// # Examples
@@ -71,7 +75,13 @@ impl<T> Vec<T> {
     /// ```
     #[inline]
     pub fn new() -> Vec<T> {
-        Vec { len: 0, cap: 0, ptr: 0 as *mut T }
+        // If we have a 0-sized vector, then the base pointer should not be NULL
+        // because an iterator over the slice will attempt to yield the base
+        // pointer as the first element in the vector, but this will end up
+        // being Some(NULL) which is optimized to None. So instead we set ptr
+        // to some arbitrary non-null value which is fine since we never call
+        // deallocate on the ptr if cap is 0.
+        Vec { len: 0, cap: 0, ptr: &PTR_MARKER as *const _ as *mut T }
     }
 
     /// Constructs a new, empty `Vec` with the specified capacity.
@@ -88,7 +98,7 @@ impl<T> Vec<T> {
     #[inline]
     pub fn with_capacity(capacity: uint) -> Vec<T> {
         if mem::size_of::<T>() == 0 {
-            Vec { len: 0, cap: uint::MAX, ptr: 0 as *mut T }
+            Vec { len: 0, cap: uint::MAX, ptr: &PTR_MARKER as *const _ as *mut T }
         } else if capacity == 0 {
             Vec::new()
         } else {
@@ -1206,15 +1216,7 @@ impl<T> Vec<T> {
     /// would also make any pointers to it invalid.
     #[inline]
     pub fn as_ptr(&self) -> *const T {
-        // If we have a 0-sized vector, then the base pointer should not be NULL
-        // because an iterator over the slice will attempt to yield the base
-        // pointer as the first element in the vector, but this will end up
-        // being Some(NULL) which is optimized to None.
-        if mem::size_of::<T>() == 0 {
-            1 as *const T
-        } else {
-            self.ptr as *const T
-        }
+        self.ptr as *const T
     }
 
     /// Returns a mutable unsafe pointer to the vector's buffer.
@@ -1226,12 +1228,7 @@ impl<T> Vec<T> {
     /// would also make any pointers to it invalid.
     #[inline]
     pub fn as_mut_ptr(&mut self) -> *mut T {
-        // see above for the 0-size check
-        if mem::size_of::<T>() == 0 {
-            1 as *mut T
-        } else {
-            self.ptr
-        }
+        self.ptr
     }
 
     /// Retains only the elements specified by the predicate.

branches/try/src/librustc/middle/trans/tvec.rs

@@ -155,8 +155,9 @@ pub fn trans_slice_vstore<'a>(
     let llcount = C_uint(ccx, count);
     let llfixed;
     if count == 0 {
-        // Zero-length array: just use NULL as the data pointer
-        llfixed = C_null(vt.llunit_ty.ptr_to());
+        // Just create a zero-sized alloca to preserve
+        // the non-null invariant of the inner slice ptr
+        llfixed = base::arrayalloca(bcx, vt.llunit_ty, llcount);
     } else {
         // Make a fixed-length backing array and allocate it on the stack.
         llfixed = base::arrayalloca(bcx, vt.llunit_ty, llcount);