compiler,runtime: pass only ptr and len to some runtime calls

This ports https://golang.org/cl/227163 to the Go frontend.
This is a step toward moving up to the go1.15rc1 release.

Original CL description:

    cmd/compile,runtime: pass only ptr and len to some runtime calls

    Some runtime calls accept a slice, but only use ptr and len.
    This change modifies most such routines to accept only ptr and len.

    After this change, the only runtime calls that accept an unnecessary
    cap arg are concatstrings and slicerunetostring.
    Neither is particularly common, and both are complicated to modify.

    Negligible compiler performance impact. Shrinks binaries a little.
    There are only a few regressions; the one I investigated was
    due to register allocation fluctuation.

    Passes 'go test -race std cmd', modulo golang/go#38265 and golang/go#38266.
    Wow, does that take a long time to run.

    file      before    after     Δ       %
    compile   19655024  19655152  +128    +0.001%
    cover     5244840   5236648   -8192   -0.156%
    dist      3662376   3658280   -4096   -0.112%
    link      6680056   6675960   -4096   -0.061%
    pprof     14789844  14777556  -12288  -0.083%
    test2json 2824744   2820648   -4096   -0.145%
    trace     11647876  11639684  -8192   -0.070%
    vet       8260472   8256376   -4096   -0.050%
    total     115163736 115118808 -44928  -0.039%

For golang/go#36890

Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/245099

5 files changed, 68 insertions, 63 deletions

diff --git a/libgo/go/runtime/cgocheck.go b/libgo/go/runtime/cgocheck.go
index c03bafe..42fdfe8 100644
--- a/libgo/go/runtime/cgocheck.go
+++ b/libgo/go/runtime/cgocheck.go
@@ -76,23 +76,24 @@ func cgoCheckMemmove(typ *_type, dst, src unsafe.Pointer, off, size uintptr) {
 	cgoCheckTypedBlock(typ, src, off, size)
 }
 
-// cgoCheckSliceCopy is called when copying n elements of a slice from
-// src to dst.  typ is the element type of the slice.
+// cgoCheckSliceCopy is called when copying n elements of a slice.
+// src and dst are pointers to the first element of the slice.
+// typ is the element type of the slice.
 // It throws if the program is copying slice elements that contain Go pointers
 // into non-Go memory.
 //go:nosplit
 //go:nowritebarrier
-func cgoCheckSliceCopy(typ *_type, dst, src slice, n int) {
+func cgoCheckSliceCopy(typ *_type, dst, src unsafe.Pointer, n int) {
 	if typ.ptrdata == 0 {
 		return
 	}
-	if !cgoIsGoPointer(src.array) {
+	if !cgoIsGoPointer(src) {
 		return
 	}
-	if cgoIsGoPointer(dst.array) {
+	if cgoIsGoPointer(dst) {
 		return
 	}
-	p := src.array
+	p := src
 	for i := 0; i < n; i++ {
 		cgoCheckTypedBlock(typ, p, 0, typ.size)
 		p = add(p, typ.size)
diff --git a/libgo/go/runtime/mbarrier.go b/libgo/go/runtime/mbarrier.go
index e66b50d..a4f9b3c 100644
--- a/libgo/go/runtime/mbarrier.go
+++ b/libgo/go/runtime/mbarrier.go
@@ -219,16 +219,14 @@ func reflect_typedmemmovepartial(typ *_type, dst, src unsafe.Pointer, off, size
 }
 
 //go:nosplit
-func typedslicecopy(typ *_type, dst, src slice) int {
-	n := dst.len
-	if n > src.len {
-		n = src.len
+func typedslicecopy(typ *_type, dstPtr unsafe.Pointer, dstLen int, srcPtr unsafe.Pointer, srcLen int) int {
+	n := dstLen
+	if n > srcLen {
+		n = srcLen
 	}
 	if n == 0 {
 		return 0
 	}
-	dstp := dst.array
-	srcp := src.array
 
 	// The compiler emits calls to typedslicecopy before
 	// instrumentation runs, so unlike the other copying and
@@ -237,19 +235,19 @@ func typedslicecopy(typ *_type, dst, src slice) int {
 	if raceenabled {
 		callerpc := getcallerpc()
 		pc := funcPC(slicecopy)
-		racewriterangepc(dstp, uintptr(n)*typ.size, callerpc, pc)
-		racereadrangepc(srcp, uintptr(n)*typ.size, callerpc, pc)
+		racewriterangepc(dstPtr, uintptr(n)*typ.size, callerpc, pc)
+		racereadrangepc(srcPtr, uintptr(n)*typ.size, callerpc, pc)
 	}
 	if msanenabled {
-		msanwrite(dstp, uintptr(n)*typ.size)
-		msanread(srcp, uintptr(n)*typ.size)
+		msanwrite(dstPtr, uintptr(n)*typ.size)
+		msanread(srcPtr, uintptr(n)*typ.size)
 	}
 
 	if writeBarrier.cgo {
-		cgoCheckSliceCopy(typ, dst, src, n)
+		cgoCheckSliceCopy(typ, dstPtr, srcPtr, n)
 	}
 
-	if dstp == srcp {
+	if dstPtr == srcPtr {
 		return n
 	}
 
@@ -259,11 +257,11 @@ func typedslicecopy(typ *_type, dst, src slice) int {
 	// before calling typedslicecopy.
 	size := uintptr(n) * typ.size
 	if writeBarrier.needed {
-		bulkBarrierPreWrite(uintptr(dstp), uintptr(srcp), size)
+		bulkBarrierPreWrite(uintptr(dstPtr), uintptr(srcPtr), size)
 	}
 	// See typedmemmove for a discussion of the race between the
 	// barrier and memmove.
-	memmove(dstp, srcp, size)
+	memmove(dstPtr, srcPtr, size)
 	return n
 }
 
@@ -293,7 +291,7 @@ func reflect_typedslicecopy(elemType *_type, dst, src slice) int {
 		memmove(dst.array, src.array, size)
 		return n
 	}
-	return typedslicecopy(elemType, dst, src)
+	return typedslicecopy(elemType, dst.array, dst.len, src.array, src.len)
 }
 
 // typedmemclr clears the typed memory at ptr with type typ. The
diff --git a/libgo/go/runtime/os_linux.go b/libgo/go/runtime/os_linux.go
index 1e86446..5d55064 100644
--- a/libgo/go/runtime/os_linux.go
+++ b/libgo/go/runtime/os_linux.go
@@ -207,13 +207,14 @@ func getHugePageSize() uintptr {
 	if fd < 0 {
 		return 0
 	}
-	n := read(fd, noescape(unsafe.Pointer(&numbuf[0])), int32(len(numbuf)))
+	ptr := noescape(unsafe.Pointer(&numbuf[0]))
+	n := read(fd, ptr, int32(len(numbuf)))
 	closefd(fd)
 	if n <= 0 {
 		return 0
 	}
-	l := n - 1 // remove trailing newline
-	v, ok := atoi(slicebytetostringtmp(numbuf[:l]))
+	n-- // remove trailing newline
+	v, ok := atoi(slicebytetostringtmp((*byte)(ptr), int(n)))
 	if !ok || v < 0 {
 		v = 0
 	}
diff --git a/libgo/go/runtime/slice.go b/libgo/go/runtime/slice.go
index b61c2b1..5197353 100644
--- a/libgo/go/runtime/slice.go
+++ b/libgo/go/runtime/slice.go
@@ -199,14 +199,14 @@ func isPowerOfTwo(x uintptr) bool {
 	return x&(x-1) == 0
 }
 
-func slicecopy(to, fm slice, width uintptr) int {
-	if fm.len == 0 || to.len == 0 {
+func slicecopy(toPtr unsafe.Pointer, toLen int, fmPtr unsafe.Pointer, fmLen int, width uintptr) int {
+	if fmLen == 0 || toLen == 0 {
 		return 0
 	}
 
-	n := fm.len
-	if to.len < n {
-		n = to.len
+	n := fmLen
+	if toLen < n {
+		n = toLen
 	}
 
 	if width == 0 {
@@ -216,43 +216,43 @@ func slicecopy(to, fm slice, width uintptr) int {
 	if raceenabled {
 		callerpc := getcallerpc()
 		pc := funcPC(slicecopy)
-		racewriterangepc(to.array, uintptr(n*int(width)), callerpc, pc)
-		racereadrangepc(fm.array, uintptr(n*int(width)), callerpc, pc)
+		racewriterangepc(toPtr, uintptr(n*int(width)), callerpc, pc)
+		racereadrangepc(fmPtr, uintptr(n*int(width)), callerpc, pc)
 	}
 	if msanenabled {
-		msanwrite(to.array, uintptr(n*int(width)))
-		msanread(fm.array, uintptr(n*int(width)))
+		msanwrite(toPtr, uintptr(n*int(width)))
+		msanread(fmPtr, uintptr(n*int(width)))
 	}
 
 	size := uintptr(n) * width
 	if size == 1 { // common case worth about 2x to do here
 		// TODO: is this still worth it with new memmove impl?
-		*(*byte)(to.array) = *(*byte)(fm.array) // known to be a byte pointer
+		*(*byte)(toPtr) = *(*byte)(fmPtr) // known to be a byte pointer
 	} else {
-		memmove(to.array, fm.array, size)
+		memmove(toPtr, fmPtr, size)
 	}
 	return n
 }
 
-func slicestringcopy(to []byte, fm string) int {
-	if len(fm) == 0 || len(to) == 0 {
+func slicestringcopy(toPtr *byte, toLen int, fm string) int {
+	if len(fm) == 0 || toLen == 0 {
 		return 0
 	}
 
 	n := len(fm)
-	if len(to) < n {
-		n = len(to)
+	if toLen < n {
+		n = toLen
 	}
 
 	if raceenabled {
 		callerpc := getcallerpc()
 		pc := funcPC(slicestringcopy)
-		racewriterangepc(unsafe.Pointer(&to[0]), uintptr(n), callerpc, pc)
+		racewriterangepc(unsafe.Pointer(toPtr), uintptr(n), callerpc, pc)
 	}
 	if msanenabled {
-		msanwrite(unsafe.Pointer(&to[0]), uintptr(n))
+		msanwrite(unsafe.Pointer(toPtr), uintptr(n))
 	}
 
-	memmove(unsafe.Pointer(&to[0]), stringStructOf(&fm).str, uintptr(n))
+	memmove(unsafe.Pointer(toPtr), stringStructOf(&fm).str, uintptr(n))
 	return n
 }
diff --git a/libgo/go/runtime/string.go b/libgo/go/runtime/string.go
index df4cae7..7b66a1b 100644
--- a/libgo/go/runtime/string.go
+++ b/libgo/go/runtime/string.go
@@ -70,47 +70,50 @@ func concatstrings(buf *tmpBuf, p *string, n int) string {
 	return s
 }
 
+// slicebytetostring converts a byte slice to a string.
+// It is inserted by the compiler into generated code.
+// ptr is a pointer to the first element of the slice;
+// n is the length of the slice.
 // Buf is a fixed-size buffer for the result,
 // it is not nil if the result does not escape.
-func slicebytetostring(buf *tmpBuf, b []byte) (str string) {
-	l := len(b)
-	if l == 0 {
+func slicebytetostring(buf *tmpBuf, ptr *byte, n int) (str string) {
+	if n == 0 {
 		// Turns out to be a relatively common case.
 		// Consider that you want to parse out data between parens in "foo()bar",
 		// you find the indices and convert the subslice to string.
 		return ""
 	}
 	if raceenabled {
-		racereadrangepc(unsafe.Pointer(&b[0]),
-			uintptr(l),
+		racereadrangepc(unsafe.Pointer(ptr),
+			uintptr(n),
 			getcallerpc(),
 			funcPC(slicebytetostring))
 	}
 	if msanenabled {
-		msanread(unsafe.Pointer(&b[0]), uintptr(l))
+		msanread(unsafe.Pointer(ptr), uintptr(n))
 	}
-	if l == 1 {
-		stringStructOf(&str).str = unsafe.Pointer(&staticbytes[b[0]])
+	if n == 1 {
+		stringStructOf(&str).str = unsafe.Pointer(&staticbytes[*ptr])
 		stringStructOf(&str).len = 1
 		return
 	}
 
 	var p unsafe.Pointer
-	if buf != nil && len(b) <= len(buf) {
+	if buf != nil && n <= len(buf) {
 		p = unsafe.Pointer(buf)
 	} else {
-		p = mallocgc(uintptr(len(b)), nil, false)
+		p = mallocgc(uintptr(n), nil, false)
 	}
 	stringStructOf(&str).str = p
-	stringStructOf(&str).len = len(b)
-	memmove(p, (*(*slice)(unsafe.Pointer(&b))).array, uintptr(len(b)))
+	stringStructOf(&str).len = n
+	memmove(p, unsafe.Pointer(ptr), uintptr(n))
 	return
 }
 
 func rawstringtmp(buf *tmpBuf, l int) (s string, b []byte) {
 	if buf != nil && l <= len(buf) {
 		b = buf[:l]
-		s = slicebytetostringtmp(b)
+		s = slicebytetostringtmp(&b[0], len(b))
 	} else {
 		s, b = rawstring(l)
 	}
@@ -131,17 +134,19 @@ func rawstringtmp(buf *tmpBuf, l int) (s string, b []byte) {
 //   where k is []byte, T1 to Tn is a nesting of struct and array literals.
 // - Used for "<"+string(b)+">" concatenation where b is []byte.
 // - Used for string(b)=="foo" comparison where b is []byte.
-func slicebytetostringtmp(b []byte) string {
-	if raceenabled && len(b) > 0 {
-		racereadrangepc(unsafe.Pointer(&b[0]),
-			uintptr(len(b)),
+func slicebytetostringtmp(ptr *byte, n int) (str string) {
+	if raceenabled && n > 0 {
+		racereadrangepc(unsafe.Pointer(ptr),
+			uintptr(n),
 			getcallerpc(),
 			funcPC(slicebytetostringtmp))
 	}
-	if msanenabled && len(b) > 0 {
-		msanread(unsafe.Pointer(&b[0]), uintptr(len(b)))
+	if msanenabled && n > 0 {
+		msanread(unsafe.Pointer(ptr), uintptr(n))
 	}
-	return *(*string)(unsafe.Pointer(&b))
+	stringStructOf(&str).str = unsafe.Pointer(ptr)
+	stringStructOf(&str).len = n
+	return
 }
 
 func stringtoslicebyte(buf *tmpBuf, s string) []byte {
@@ -232,7 +237,7 @@ func intstring(buf *[4]byte, v int64) (s string) {
 	var b []byte
 	if buf != nil {
 		b = buf[:]
-		s = slicebytetostringtmp(b)
+		s = slicebytetostringtmp(&b[0], len(b))
 	} else {
 		s, b = rawstring(4)
 	}