From bb9e850246092d3931080ddbac551a0857b28364 Mon Sep 17 00:00:00 2001 From: Manish Goregaokar Date: Fri, 13 Oct 2017 13:09:35 -0400 Subject: [PATCH 1/2] std: Get rid of hash_offet in RawTable This offset is always zero, and we don't consistently take it into account. This is okay, because it's zero, but if it ever changes we're going to have bugs (e.g. in the `dealloc` call, where we don't take it into account). It's better to remove this for now; if we ever have a need for a nonzero offset we can add it back, and handle it properly when we do so. --- src/libstd/collections/hash/table.rs | 31 ++++++++++++++-------------- 1 file changed, 15 insertions(+), 16 deletions(-) diff --git a/src/libstd/collections/hash/table.rs b/src/libstd/collections/hash/table.rs index 93929637e2f1e..527c4ef4592cd 100644 --- a/src/libstd/collections/hash/table.rs +++ b/src/libstd/collections/hash/table.rs @@ -717,26 +717,25 @@ fn calculate_offsets(hashes_size: usize, (pairs_offset, end_of_pairs, oflo) } -// Returns a tuple of (minimum required malloc alignment, hash_offset, +// Returns a tuple of (minimum required malloc alignment, // array_size), from the start of a mallocated array. fn calculate_allocation(hash_size: usize, hash_align: usize, pairs_size: usize, pairs_align: usize) - -> (usize, usize, usize, bool) { - let hash_offset = 0; + -> (usize, usize, bool) { let (_, end_of_pairs, oflo) = calculate_offsets(hash_size, pairs_size, pairs_align); let align = cmp::max(hash_align, pairs_align); - (align, hash_offset, end_of_pairs, oflo) + (align, end_of_pairs, oflo) } #[test] fn test_offset_calculation() { - assert_eq!(calculate_allocation(128, 8, 16, 8), (8, 0, 144, false)); - assert_eq!(calculate_allocation(3, 1, 2, 1), (1, 0, 5, false)); - assert_eq!(calculate_allocation(6, 2, 12, 4), (4, 0, 20, false)); + assert_eq!(calculate_allocation(128, 8, 16, 8), (8, 144, false)); + assert_eq!(calculate_allocation(3, 1, 2, 1), (1, 5, false)); + assert_eq!(calculate_allocation(6, 2, 12, 4), (4, 20, false)); assert_eq!(calculate_offsets(128, 15, 4), (128, 143, false)); assert_eq!(calculate_offsets(3, 2, 4), (4, 6, false)); assert_eq!(calculate_offsets(6, 12, 4), (8, 20, false)); @@ -768,10 +767,10 @@ impl RawTable { // This is great in theory, but in practice getting the alignment // right is a little subtle. Therefore, calculating offsets has been // factored out into a different function. - let (alignment, hash_offset, size, oflo) = calculate_allocation(hashes_size, - align_of::(), - pairs_size, - align_of::<(K, V)>()); + let (alignment, size, oflo) = calculate_allocation(hashes_size, + align_of::(), + pairs_size, + align_of::<(K, V)>()); assert!(!oflo, "capacity overflow"); // One check for overflow that covers calculation and rounding of size. @@ -784,7 +783,7 @@ impl RawTable { let buffer = Heap.alloc(Layout::from_size_align(size, alignment).unwrap()) .unwrap_or_else(|e| Heap.oom(e)); - let hashes = buffer.offset(hash_offset as isize) as *mut HashUint; + let hashes = buffer as *mut HashUint; RawTable { capacity_mask: capacity.wrapping_sub(1), @@ -1183,10 +1182,10 @@ unsafe impl<#[may_dangle] K, #[may_dangle] V> Drop for RawTable { let hashes_size = self.capacity() * size_of::(); let pairs_size = self.capacity() * size_of::<(K, V)>(); - let (align, _, size, oflo) = calculate_allocation(hashes_size, - align_of::(), - pairs_size, - align_of::<(K, V)>()); + let (align, size, oflo) = calculate_allocation(hashes_size, + align_of::(), + pairs_size, + align_of::<(K, V)>()); debug_assert!(!oflo, "should be impossible"); From e8e7715bebdd401ebacfabb66928d0f7e4733120 Mon Sep 17 00:00:00 2001 From: Manish Goregaokar Date: Fri, 13 Oct 2017 13:19:15 -0400 Subject: [PATCH 2/2] std: Set probe length tag on cloned hashmaps This isn't strictly necessary for hashmap cloning to work. The tag is used to hint for an upcoming resize, so it's good to copy this information over. (We can do cleverer things like actually resizing the hashmap when we see the tag, or even cleaning up the entry order, but this requires more thought and might not be worth it) --- src/libstd/collections/hash/table.rs | 1 + 1 file changed, 1 insertion(+) diff --git a/src/libstd/collections/hash/table.rs b/src/libstd/collections/hash/table.rs index 527c4ef4592cd..7e623a0af17c3 100644 --- a/src/libstd/collections/hash/table.rs +++ b/src/libstd/collections/hash/table.rs @@ -1156,6 +1156,7 @@ impl Clone for RawTable { } new_ht.size = self.size(); + new_ht.set_tag(self.tag()); new_ht }