cmd/compile: optimize len check when make slice
In CL 226278, we did:
if len < 0 { panicmakeslicelen }
if len > cap { panicmakeslicecap }
But due to the fact that cap is constrained to [0,2^31), so it is safe
to do:
if uint64(len) > cap {
if len < 0 { panicmakeslicelen() }
panicmakeslicecap()
}
save us a comparison in common case when len is within range.
Passes toolstash-check.
Change-Id: I0ebd52914ccde4cbb45f16c9e020b0c8f42e0663
Reviewed-on: https://go-review.googlesource.com/c/go/+/226737
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
diff --git a/src/cmd/compile/internal/gc/walk.go b/src/cmd/compile/internal/gc/walk.go
index dfc9d9a..14d088c 100644
--- a/src/cmd/compile/internal/gc/walk.go
+++ b/src/cmd/compile/internal/gc/walk.go
@@ -1338,15 +1338,16 @@
Fatalf("walkexpr: invalid index %v", r)
}
- // if len < 0 { panicmakeslicelen }
- nif := nod(OIF, nod(OLT, l, nodintconst(0)), nil)
- nif.Nbody.Set1(mkcall("panicmakeslicelen", nil, init))
- nif = typecheck(nif, ctxStmt)
- init.Append(nif)
-
- // if len > cap { panicmakeslicecap }
- nif = nod(OIF, nod(OGT, conv(l, types.Types[TUINT64]), nodintconst(i)), nil)
- nif.Nbody.Set1(mkcall("panicmakeslicecap", nil, init))
+ // cap is constrained to [0,2^31), so it's safe to do:
+ //
+ // if uint64(len) > cap {
+ // if len < 0 { panicmakeslicelen() }
+ // panicmakeslicecap()
+ // }
+ nif := nod(OIF, nod(OGT, conv(l, types.Types[TUINT64]), nodintconst(i)), nil)
+ niflen := nod(OIF, nod(OLT, l, nodintconst(0)), nil)
+ niflen.Nbody.Set1(mkcall("panicmakeslicelen", nil, init))
+ nif.Nbody.Append(niflen, mkcall("panicmakeslicecap", nil, init))
nif = typecheck(nif, ctxStmt)
init.Append(nif)
