Commit d12c0bf90911339c8db0741b257eac251b827b2c | zig

author	Andrew Kelley <andrew@ziglang.org> 2024-12-16 07:27:20-05:00
committer	GitHub <noreply@github.com> 2024-12-16 07:27:20-05:00
log	d12c0bf90911339c8db0741b257eac251b827b2c
tree	a35c9b98cc1e601c09e96983548e2a62c8ad0625
parent	3a0a9aa9b866ad8483d298c6b891f9b321303bb9
parent	0fe17ea12a5bc389d8cb0c87027a112a552e9cbc
signature	Signed by PGP key B5690EEEBB952194

Merge pull request #22242 from Rexicon226/moar-branch-hint

utilize `@branchHint` more

2 files changed, 9 insertions(+), 13 deletions(-)

lib
- std
  - hash
    xxhash.zig
  - hash_map.zig

lib/std/hash/xxhash.zig+5-5

lib/std/hash_map.zig+4-8

 @@ -1187,17 +1187,13 @@ pub fn HashMapUnmanaged(
         }
         /// Find the index containing the data for the given key.
-        /// Whether this function returns null is almost always
+        fn getIndex(self: Self, key: anytype, ctx: anytype) ?usize {
-        /// branched on after this function returns, and this function
-        /// returns null/not null from separate code paths.  We
-        /// want the optimizer to remove that branch and instead directly
-        /// fuse the basic blocks after the branch to the basic blocks
-        /// from this function.  To encourage that, this function is
-        /// marked as inline.
-        inline fn getIndex(self: Self, key: anytype, ctx: anytype) ?usize {
             comptime verifyContext(@TypeOf(ctx), @TypeOf(key), K, Hash, false);
             if (self.size == 0) {
+                // We use cold instead of unlikely to force a jump to this case,
+                // no matter the weight of the opposing side.
+                @branchHint(.cold);
                 return null;
             }

...	@@ -593,7 +593,7 @@ pub const XxHash3 = struct {	...	@@ -593,7 +593,7 @@ pub const XxHash3 = struct {
593	}	593	}
594		594
595	fn hash3(seed: u64, input: anytype, noalias secret: *const [192]u8) u64 {	595	fn hash3(seed: u64, input: anytype, noalias secret: *const [192]u8) u64 {
596	@branchHint(.cold);	596	@branchHint(.unlikely);
597	std.debug.assert(input.len > 0 and input.len < 4);	597	std.debug.assert(input.len > 0 and input.len < 4);
598		598
599	const flip: [2]u32 = @bitCast(secret[0..8].*);	599	const flip: [2]u32 = @bitCast(secret[0..8].*);
...	@@ -625,7 +625,7 @@ pub const XxHash3 = struct {	...	@@ -625,7 +625,7 @@ pub const XxHash3 = struct {
625	}	625	}
626		626
627	fn hash16(seed: u64, input: anytype, noalias secret: *const [192]u8) u64 {	627	fn hash16(seed: u64, input: anytype, noalias secret: *const [192]u8) u64 {
628	@branchHint(.cold);	628	@branchHint(.unlikely);
629	std.debug.assert(input.len > 8 and input.len <= 16);	629	std.debug.assert(input.len > 8 and input.len <= 16);
630		630
631	const flip: [4]u64 = @bitCast(secret[24..56].*);	631	const flip: [4]u64 = @bitCast(secret[24..56].*);
...	@@ -641,7 +641,7 @@ pub const XxHash3 = struct {	...	@@ -641,7 +641,7 @@ pub const XxHash3 = struct {
641	}	641	}
642		642
643	fn hash128(seed: u64, input: anytype, noalias secret: *const [192]u8) u64 {	643	fn hash128(seed: u64, input: anytype, noalias secret: *const [192]u8) u64 {
644	@branchHint(.cold);	644	@branchHint(.unlikely);
645	std.debug.assert(input.len > 16 and input.len <= 128);	645	std.debug.assert(input.len > 16 and input.len <= 128);
646		646
647	var acc = XxHash64.prime_1 *% @as(u64, input.len);	647	var acc = XxHash64.prime_1 *% @as(u64, input.len);
...	@@ -657,7 +657,7 @@ pub const XxHash3 = struct {	...	@@ -657,7 +657,7 @@ pub const XxHash3 = struct {
657	}	657	}
658		658
659	fn hash240(seed: u64, input: anytype, noalias secret: *const [192]u8) u64 {	659	fn hash240(seed: u64, input: anytype, noalias secret: *const [192]u8) u64 {
660	@branchHint(.cold);	660	@branchHint(.unlikely);
661	std.debug.assert(input.len > 128 and input.len <= 240);	661	std.debug.assert(input.len > 128 and input.len <= 240);
662		662
663	var acc = XxHash64.prime_1 *% @as(u64, input.len);	663	var acc = XxHash64.prime_1 *% @as(u64, input.len);
...	@@ -676,7 +676,7 @@ pub const XxHash3 = struct {	...	@@ -676,7 +676,7 @@ pub const XxHash3 = struct {
676	}	676	}
677		677
678	noinline fn hashLong(seed: u64, input: []const u8) u64 {	678	noinline fn hashLong(seed: u64, input: []const u8) u64 {
679	@branchHint(.cold);	679	@branchHint(.unlikely);
680	std.debug.assert(input.len >= 240);	680	std.debug.assert(input.len >= 240);
681		681
682	const block_count = ((input.len - 1) / @sizeOf(Block)) * @sizeOf(Block);	682	const block_count = ((input.len - 1) / @sizeOf(Block)) * @sizeOf(Block);