unsafe: optimize Slice bounds checking
This reduces the number of branches to bounds check non-empty slices
from 5 to 3. It does also increase the number of branches to handle
empty slices from 1 to 3; but for non-panicking calls, they should all
be predictable.
Updates #48798.
Change-Id: I3ffa66857096486f4dee417e1a66eb8fdf7a3777
Reviewed-on: https://go-review.googlesource.com/c/go/+/355490
Trust: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/src/runtime/slice.go b/src/runtime/slice.go
index 66bb7d9..aab8a59 100644
--- a/src/runtime/slice.go
+++ b/src/runtime/slice.go
@@ -115,16 +115,15 @@
}
func unsafeslice(et *_type, ptr unsafe.Pointer, len int) {
- if len == 0 {
- return
- }
-
- if ptr == nil {
- panic(errorString("unsafe.Slice: ptr is nil and len is not zero"))
+ if len < 0 {
+ panicunsafeslicelen()
}
mem, overflow := math.MulUintptr(et.size, uintptr(len))
- if overflow || mem > -uintptr(ptr) || len < 0 {
+ if overflow || mem > -uintptr(ptr) {
+ if ptr == nil {
+ panic(errorString("unsafe.Slice: ptr is nil and len is not zero"))
+ }
panicunsafeslicelen()
}
}
