runtime/coverage: use unsafe.Slice, not reflect.SliceHeader

Change-Id: I59c4757df83c12b4c8b85cdd523552c5e5e7bf95
Reviewed-on: https://go-review.googlesource.com/c/go/+/508977
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>

diff --git a/src/runtime/coverage/apis.go b/src/runtime/coverage/apis.go
index 05da345ede8d1413add3577ea547f622d18e2c3b..15ba04a86f9cd0dc3ae3d9cfb833c2c931f7d91c 100644 (file)
--- a/src/runtime/coverage/apis.go
+++ b/src/runtime/coverage/apis.go
@@ -8,7 +8,6 @@ import (
        "fmt"
        "internal/coverage"
        "io"
-       "reflect"
        "sync/atomic"
        "unsafe"
 )
@@ -158,13 +157,8 @@ func ClearCounters() error {
        // inconsistency when reading the counter array from the thread
        // running ClearCounters.
 
-       var sd []atomic.Uint32
-
-       bufHdr := (*reflect.SliceHeader)(unsafe.Pointer(&sd))
        for _, c := range cl {
-               bufHdr.Data = uintptr(unsafe.Pointer(c.Counters))
-               bufHdr.Len = int(c.Len)
-               bufHdr.Cap = int(c.Len)
+               sd := unsafe.Slice((*atomic.Uint32)(unsafe.Pointer(c.Counters)), int(c.Len))
                for i := 0; i < len(sd); i++ {
                        // Skip ahead until the next non-zero value.
                        sdi := sd[i].Load()

diff --git a/src/runtime/coverage/emit.go b/src/runtime/coverage/emit.go
index bb0c6fb6a2fba7c580cf0a671a19a79ff07e3cb6..d18e69053d3fb7370cb0b7694dbfb5af65f53d3e 100644 (file)
--- a/src/runtime/coverage/emit.go
+++ b/src/runtime/coverage/emit.go
@@ -14,7 +14,6 @@ import (
        "io"
        "os"
        "path/filepath"
-       "reflect"
        "runtime"
        "strconv"
        "sync/atomic"
@@ -447,26 +446,16 @@ func (s *emitState) needMetaDataFile() bool {
 func writeMetaData(w io.Writer, metalist []rtcov.CovMetaBlob, cmode coverage.CounterMode, gran coverage.CounterGranularity, finalHash [16]byte) error {
        mfw := encodemeta.NewCoverageMetaFileWriter("<io.Writer>", w)
 
-       // Note: "sd" is re-initialized on each iteration of the loop
-       // below, and would normally be declared inside the loop, but
-       // placed here escape analysis since we capture it in bufHdr.
-       var sd []byte
-       bufHdr := (*reflect.SliceHeader)(unsafe.Pointer(&sd))
-
        var blobs [][]byte
        for _, e := range metalist {
-               bufHdr.Data = uintptr(unsafe.Pointer(e.P))
-               bufHdr.Len = int(e.Len)
-               bufHdr.Cap = int(e.Len)
+               sd := unsafe.Slice(e.P, int(e.Len))
                blobs = append(blobs, sd)
        }
        return mfw.Write(finalHash, blobs, cmode, gran)
 }
 
 func (s *emitState) VisitFuncs(f encodecounter.CounterVisitorFn) error {
-       var sd []atomic.Uint32
        var tcounters []uint32
-       bufHdr := (*reflect.SliceHeader)(unsafe.Pointer(&sd))
 
        rdCounters := func(actrs []atomic.Uint32, ctrs []uint32) []uint32 {
                ctrs = ctrs[:0]
@@ -478,9 +467,7 @@ func (s *emitState) VisitFuncs(f encodecounter.CounterVisitorFn) error {
 
        dpkg := uint32(0)
        for _, c := range s.counterlist {
-               bufHdr.Data = uintptr(unsafe.Pointer(c.Counters))
-               bufHdr.Len = int(c.Len)
-               bufHdr.Cap = int(c.Len)
+               sd := unsafe.Slice((*atomic.Uint32)(unsafe.Pointer(c.Counters)), int(c.Len))
                for i := 0; i < len(sd); i++ {
                        // Skip ahead until the next non-zero value.
                        sdi := sd[i].Load()