cmd/compile: use jump tables for large type switches

For large interface -> concrete type switches, we can use a jump
table on some bits of the type hash instead of a binary search on
the type hash.

name                        old time/op  new time/op  delta
SwitchTypePredictable-24    1.99ns ± 2%  1.78ns ± 5%  -10.87%  (p=0.000 n=10+10)
SwitchTypeUnpredictable-24  11.0ns ± 1%   9.1ns ± 2%  -17.55%  (p=0.000 n=7+9)

Change-Id: Ida4768e5d62c3ce1c2701288b72664aaa9e64259
Reviewed-on: https://go-review.googlesource.com/c/go/+/521497
Reviewed-by: Keith Randall <khr@google.com>
Auto-Submit: Keith Randall <khr@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Run-TryBot: Keith Randall <khr@golang.org>

1 files changed, 19 insertions, 0 deletions

diff --git a/test/codegen/switch.go b/test/codegen/switch.go
index 603e0befbb..556d02a162 100644
--- a/test/codegen/switch.go
+++ b/test/codegen/switch.go
@@ -99,3 +99,22 @@ func mimetype(ext string) string {
 		return ""
 	}
 }
+
+// use jump tables for type switches to concrete types.
+func typeSwitch(x any) int {
+	// amd64:`JMP\s\(.*\)\(.*\)$`
+	// arm64:`MOVD\s\(R.*\)\(R.*<<3\)`,`JMP\s\(R.*\)$`
+	switch x.(type) {
+	case int:
+		return 0
+	case int8:
+		return 1
+	case int16:
+		return 2
+	case int32:
+		return 3
+	case int64:
+		return 4
+	}
+	return 7
+}