Commit 2b677d1660018434757f9c9efec3c712675e6c47 | zig

author	Matthew Lugg <mlugg@mlugg.co.uk> 2024-06-20 08:38:23+01:00
committer	Matthew Lugg <mlugg@mlugg.co.uk> 2024-06-20 08:41:07+01:00
log	2b677d1660018434757f9c9efec3c712675e6c47
tree	b0c05ac895e1e42abca677a135caf34d15173d24
parent	6a8cf25a8aea11ef80b48c9bce59d0aafcff3297
signature	Commit is signed but in an unrecognized format.

Sema: fix performance regression

LLVM fails to notice that in release builds, `logFn` ignores its
arguments, so their computation can be elided. So, LLVM fails to elide
this hashmap lookup. Its cost isn't too significant, but doing it in the
hottest loop in Sema adds up!

Technically, we could do the lookup a single time, before the loop, but
it was cleanest (and a little faster) to just disable this log call at
comptime when debug logging is disabled.

1 files changed, 10 insertions(+), 5 deletions(-)

src
- Sema.zig

src/Sema.zig+10-5

...	...	@@ -992,11 +992,16 @@ fn analyzeBodyInner(
992	992	while (true) {
993	993	crash_info.setBodyIndex(i);
994	994	const inst = body[i];
995		std.log.scoped(.sema_zir).debug("sema ZIR {s} %{d}", .{ sub_file_path: {
996		const path_digest = block.src_base_inst.resolveFull(&mod.intern_pool).path_digest;
997		const index = mod.path_digest_map.getIndex(path_digest).?;
998		break :sub_file_path mod.import_table.values()[index].sub_file_path;
999		}, inst });
	995
	996	// The hashmap lookup in here is a little expensive, and LLVM fails to optimize it away.
	997	if (build_options.enable_logging) {
	998	std.log.scoped(.sema_zir).debug("sema ZIR {s} %{d}", .{ sub_file_path: {
	999	const path_digest = block.src_base_inst.resolveFull(&mod.intern_pool).path_digest;
	1000	const index = mod.path_digest_map.getIndex(path_digest).?;
	1001	break :sub_file_path mod.import_table.values()[index].sub_file_path;
	1002	}, inst });
	1003	}
	1004
1000	1005	const air_inst: Air.Inst.Ref = switch (tags[@intFromEnum(inst)]) {
1001	1006	// zig fmt: off
1002	1007	.alloc => try sema.zirAlloc(block, inst),