Commit 57f545eed8e940520855c127245414db9ea29310 | zig

author	Ryan Liptak <squeek502@hotmail.com> 2019-04-25 13:35:45-07:00
committer	Ryan Liptak <squeek502@hotmail.com> 2019-04-25 13:35:45-07:00
log	57f545eed8e940520855c127245414db9ea29310
tree	6249362202402aad3ad4707fc7d237cbbd27f090
parent	8ce130de3cf38e09cfbcbd1b22da34ae5b27a040

std.heap.DirectAllocator: reduce the amount of redundant memcpy calls on Windows

Previously the memory would be copied to a different aligned address in some cases where the old offset could have been used. This fixes it so that it will always try to use the old offset when possible, and only uses a different offset if the old one is truly invalid (not aligned or not enough space to store the alloc at the old offset).

1 files changed, 10 insertions(+), 6 deletions(-)

std
- heap.zig

std/heap.zig+10-6

 @@ -170,16 +170,20 @@ pub const DirectAllocator = struct {
                 ) orelse return error.OutOfMemory;
                 const offset = old_adjusted_addr - root_addr;
                 const new_root_addr = @ptrToInt(new_ptr);
-                const adjusted_addr = new_root_addr + offset;
+                var new_adjusted_addr = new_root_addr + offset;
-                const new_adjusted_addr = mem.alignForward(new_root_addr, new_align);
+                const offset_is_valid = new_adjusted_addr + new_size + @sizeOf(usize) <= new_root_addr + amt;
-                // If HeapReAlloc didn't happen to move the memory to the new alignment
+                const offset_is_aligned = new_adjusted_addr % new_align == 0;
-                // then we need to copy it
+                if (!offset_is_valid or !offset_is_aligned) {
-                if (new_adjusted_addr != adjusted_addr) {
+                    // If HeapReAlloc didn't happen to move the memory to the new alignment,
+                    // or the memory starting at the old offset would be outside of the new allocation,
+                    // then we need to copy the memory to a valid aligned address and use that
+                    const new_aligned_addr = mem.alignForward(new_root_addr, new_align);
                     @memcpy(
+                        @intToPtr([*]u8, new_aligned_addr),
                         @intToPtr([*]u8, new_adjusted_addr),
-                        @intToPtr([*]u8, adjusted_addr),
                         std.math.min(old_mem.len, new_size),
                     );
+                    new_adjusted_addr = new_aligned_addr;
                 }
                 const new_record_addr = new_adjusted_addr + new_size;
                 @intToPtr(*align(1) usize, new_record_addr).* = new_root_addr;