Auto merge of #42331 - retep998:standard-relocation-coupon, r=alexcrichton

Improve reallocation in alloc_system on Windows

Fixes https://github.com/rust-lang/rust/issues/42025

src/liballoc_system/lib.rs

@@ -171,6 +171,8 @@ pub fn usable_size(size: usize, _align: usize) -> usize {
 #[cfg(windows)]
 #[allow(bad_style)]
 mod imp {
+    use core::cmp::min;
+    use core::ptr::copy_nonoverlapping;
     use MIN_ALIGN;
 
     type LPVOID = *mut u8;
@@ -225,19 +227,16 @@ pub unsafe fn allocate_zeroed(size: usize, align: usize) -> *mut u8 {
         allocate_with_flags(size, align, HEAP_ZERO_MEMORY)
     }
 
-    pub unsafe fn reallocate(ptr: *mut u8, _old_size: usize, size: usize, align: usize) -> *mut u8 {
+    pub unsafe fn reallocate(ptr: *mut u8, old_size: usize, size: usize, align: usize) -> *mut u8 {
         if align <= MIN_ALIGN {
             HeapReAlloc(GetProcessHeap(), 0, ptr as LPVOID, size as SIZE_T) as *mut u8
         } else {
-            let header = get_header(ptr);
-            let new = HeapReAlloc(GetProcessHeap(),
-                                  0,
-                                  header.0 as LPVOID,
-                                  (size + align) as SIZE_T) as *mut u8;
-            if new.is_null() {
-                return new;
+            let new = allocate(size, align);
+            if !new.is_null() {
+                copy_nonoverlapping(ptr, new, min(size, old_size));
+                deallocate(ptr, old_size, align);
             }
-            align_ptr(new, align)
+            new
         }
     }
 
@@ -246,15 +245,19 @@ pub unsafe fn reallocate_inplace(ptr: *mut u8,
                                      size: usize,
                                      align: usize)
                                      -> usize {
-        if align <= MIN_ALIGN {
-            let new = HeapReAlloc(GetProcessHeap(),
-                                  HEAP_REALLOC_IN_PLACE_ONLY,
-                                  ptr as LPVOID,
-                                  size as SIZE_T) as *mut u8;
-            if new.is_null() { old_size } else { size }
+        let new = if align <= MIN_ALIGN {
+            HeapReAlloc(GetProcessHeap(),
+                        HEAP_REALLOC_IN_PLACE_ONLY,
+                        ptr as LPVOID,
+                        size as SIZE_T) as *mut u8
         } else {
-            old_size
-        }
+            let header = get_header(ptr);
+            HeapReAlloc(GetProcessHeap(),
+                        HEAP_REALLOC_IN_PLACE_ONLY,
+                        header.0 as LPVOID,
+                        size + align as SIZE_T) as *mut u8
+        };
+        if new.is_null() { old_size } else { size }
     }
 
     pub unsafe fn deallocate(ptr: *mut u8, _old_size: usize, align: usize) {

src/libcollections/tests/lib.rs

@@ -10,6 +10,7 @@
 
 #![deny(warnings)]
 
+#![feature(attr_literals)]
 #![feature(box_syntax)]
 #![feature(inclusive_range_syntax)]
 #![feature(collection_placement)]
@@ -20,6 +21,7 @@
 #![feature(pattern)]
 #![feature(placement_in_syntax)]
 #![feature(rand)]
+#![feature(repr_align)]
 #![feature(slice_rotate)]
 #![feature(splice)]
 #![feature(str_escape)]

src/libcollections/tests/vec.rs

@@ -781,3 +781,18 @@ fn from_into_inner() {
     assert_eq!(vec, [2, 3]);
     assert!(ptr != vec.as_ptr());
 }
+
+#[test]
+fn overaligned_allocations() {
+    #[repr(align(256))]
+    struct Foo(usize);
+    let mut v = vec![Foo(273)];
+    for i in 0..0x1000 {
+        v.reserve_exact(i);
+        assert!(v[0].0 == 273);
+        assert!(v.as_ptr() as usize & 0xff == 0);
+        v.shrink_to_fit();
+        assert!(v[0].0 == 273);
+        assert!(v.as_ptr() as usize & 0xff == 0);
+    }
+}