cmd/internal/gc, runtime: speed up some cases of _, ok := i.(T)
Some type assertions of the form _, ok := i.(T) allow efficient inlining.
Such type assertions commonly show up in type switches.
For example, with this optimization, using 6g, the length of
encoding/binary's intDataSize function shrinks from 2224 to 1728 bytes (-22%).
benchmark old ns/op new ns/op delta
BenchmarkAssertI2E2Blank 4.67 0.82 -82.44%
BenchmarkAssertE2T2Blank 4.38 0.83 -81.05%
BenchmarkAssertE2E2Blank 3.88 0.83 -78.61%
BenchmarkAssertE2E2 14.2 14.4 +1.41%
BenchmarkAssertE2T2 10.3 10.4 +0.97%
BenchmarkAssertI2E2 13.4 13.3 -0.75%
Change-Id: Ie9798c3e85432bb8e0f2c723afc376e233639df7
Reviewed-on: https://go-review.googlesource.com/7697
Reviewed-by: Keith Randall <khr@golang.org>
diff --git a/src/cmd/internal/gc/walk.go b/src/cmd/internal/gc/walk.go
index e55b415..1626c11 100644
--- a/src/cmd/internal/gc/walk.go
+++ b/src/cmd/internal/gc/walk.go
@@ -869,6 +869,32 @@
oktype = ok.Type
}
+ fromKind := type2IET(from.Type)
+ toKind := type2IET(t)
+
+ // Avoid runtime calls in a few cases of the form _, ok := i.(T).
+ // This is faster and shorter and allows the corresponding assertX2X2
+ // routines to skip nil checks on their last argument.
+ if isblank(n.List.N) {
+ var fast *Node
+ switch {
+ case fromKind == "E" && toKind == "T":
+ tab := Nod(OITAB, from, nil) // type:eface::tab:iface
+ typ := Nod(OCONVNOP, typename(t), nil)
+ typ.Type = Ptrto(Types[TUINTPTR])
+ fast = Nod(OEQ, tab, typ)
+ case fromKind == "I" && toKind == "E",
+ fromKind == "E" && toKind == "E":
+ tab := Nod(OITAB, from, nil)
+ fast = Nod(ONE, tab, nodnil())
+ }
+ if fast != nil {
+ n = Nod(OAS, ok, fast)
+ typecheck(&n, Etop)
+ goto ret
+ }
+ }
+
var resptr *Node // &res
if isblank(n.List.N) {
resptr = nodnil()
@@ -877,7 +903,7 @@
}
resptr.Etype = 1 // addr does not escape
- buf := "assert" + type2IET(from.Type) + "2" + type2IET(t) + "2"
+ buf := "assert" + fromKind + "2" + toKind + "2"
fn := syslook(buf, 1)
substArgTypes(fn, from.Type, t)
call := mkcall1(fn, oktype, init, typename(t), from, resptr)
