runtime: auto-generate duff routines

This makes it easier to experiment with alternative implementations.

While we're here, update the comments.

No functional changes. Passes toolstash -cmp.

Change-Id: I428535754908f0fdd7cc36c214ddb6e1e60f376e
Reviewed-on: https://go-review.googlesource.com/8310
Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

1 files changed, 180 insertions, 0 deletions

diff --git a/src/runtime/mkduff.go b/src/runtime/mkduff.go
new file mode 100644
index 0000000000..d0f1e1ba9f
--- /dev/null
+++ b/src/runtime/mkduff.go
@@ -0,0 +1,180 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build ignore
+
+// runtime·duffzero is a Duff's device for zeroing memory.
+// The compiler jumps to computed addresses within
+// the routine to zero chunks of memory.
+// Do not change duffzero without also
+// changing clearfat in cmd/?g/ggen.go.
+
+// runtime·duffcopy is a Duff's device for copying memory.
+// The compiler jumps to computed addresses within
+// the routine to copy chunks of memory.
+// Source and destination must not overlap.
+// Do not change duffcopy without also
+// changing stackcopy in cmd/?g/cgen.go.
+
+// See the zero* and copy* generators below
+// for architecture-specific comments.
+
+// mkduff generates duff_*.s.
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"log"
+)
+
+func main() {
+	gen("amd64", notags, zeroAMD64, copyAMD64)
+	gen("386", notags, zero386, copy386)
+	gen("arm", notags, zeroARM, copyARM)
+	gen("arm64", notags, zeroARM64, copyARM64)
+	gen("ppc64x", tagsPPC64x, zeroPPC64x, copyPPC64x)
+}
+
+func gen(arch string, tags, zero, copy func(io.Writer)) {
+	var buf bytes.Buffer
+
+	fmt.Fprintln(&buf, "// AUTO-GENERATED by mkduff.go")
+	fmt.Fprintln(&buf, "// Run go generate from src/runtime to update.")
+	fmt.Fprintln(&buf, "// See mkduff.go for comments.")
+	tags(&buf)
+	fmt.Fprintln(&buf, "#include \"textflag.h\"")
+	fmt.Fprintln(&buf)
+	zero(&buf)
+	fmt.Fprintln(&buf)
+	copy(&buf)
+
+	if err := ioutil.WriteFile("duff_"+arch+".s", buf.Bytes(), 0644); err != nil {
+		log.Fatalln(err)
+	}
+}
+
+func notags(w io.Writer) { fmt.Fprintln(w) }
+
+func zeroAMD64(w io.Writer) {
+	// AX: zero
+	// DI: ptr to memory to be zeroed
+	// DI is updated as a side effect.
+	fmt.Fprintln(w, "TEXT runtime·duffzero(SB), NOSPLIT, $0-0")
+	for i := 0; i < 128; i++ {
+		fmt.Fprintln(w, "\tSTOSQ")
+	}
+	fmt.Fprintln(w, "\tRET")
+}
+
+func copyAMD64(w io.Writer) {
+	// SI: ptr to source memory
+	// DI: ptr to destination memory
+	// SI and DI are updated as a side effect.
+	//
+	// This is equivalent to a sequence of MOVSQ but
+	// for some reason that is 3.5x slower than this code.
+	// The STOSQ in duffzero seem fine, though.
+	fmt.Fprintln(w, "TEXT runtime·duffcopy(SB), NOSPLIT, $0-0")
+	for i := 0; i < 128; i++ {
+		fmt.Fprintln(w, "\tMOVQ\t(SI), CX")
+		fmt.Fprintln(w, "\tADDQ\t$8, SI")
+		fmt.Fprintln(w, "\tMOVQ\tCX, (DI)")
+		fmt.Fprintln(w, "\tADDQ\t$8, DI")
+		fmt.Fprintln(w)
+	}
+	fmt.Fprintln(w, "\tRET")
+}
+
+func zero386(w io.Writer) {
+	// AX: zero
+	// DI: ptr to memory to be zeroed
+	// DI is updated as a side effect.
+	fmt.Fprintln(w, "TEXT runtime·duffzero(SB), NOSPLIT, $0-0")
+	for i := 0; i < 128; i++ {
+		fmt.Fprintln(w, "\tSTOSL")
+	}
+	fmt.Fprintln(w, "\tRET")
+}
+
+func copy386(w io.Writer) {
+	// SI: ptr to source memory
+	// DI: ptr to destination memory
+	// SI and DI are updated as a side effect.
+	//
+	// This is equivalent to a sequence of MOVSL but
+	// for some reason MOVSL is really slow.
+	fmt.Fprintln(w, "TEXT runtime·duffcopy(SB), NOSPLIT, $0-0")
+	for i := 0; i < 128; i++ {
+		fmt.Fprintln(w, "\tMOVL\t(SI), CX")
+		fmt.Fprintln(w, "\tADDL\t$4, SI")
+		fmt.Fprintln(w, "\tMOVL\tCX, (DI)")
+		fmt.Fprintln(w, "\tADDL\t$4, DI")
+		fmt.Fprintln(w)
+	}
+	fmt.Fprintln(w, "\tRET")
+}
+
+func zeroARM(w io.Writer) {
+	// R0: zero
+	// R1: ptr to memory to be zeroed
+	// R1 is updated as a side effect.
+	fmt.Fprintln(w, "TEXT runtime·duffzero(SB), NOSPLIT, $0-0")
+	for i := 0; i < 128; i++ {
+		fmt.Fprintln(w, "\tMOVW.P\tR0, 4(R1)")
+	}
+	fmt.Fprintln(w, "\tRET")
+}
+
+func copyARM(w io.Writer) {
+	// R0: scratch space
+	// R1: ptr to source memory
+	// R2: ptr to destination memory
+	// R1 and R2 are updated as a side effect
+	fmt.Fprintln(w, "TEXT runtime·duffcopy(SB), NOSPLIT, $0-0")
+	for i := 0; i < 128; i++ {
+		fmt.Fprintln(w, "\tMOVW.P\t4(R1), R0")
+		fmt.Fprintln(w, "\tMOVW.P\tR0, 4(R2)")
+		fmt.Fprintln(w)
+	}
+	fmt.Fprintln(w, "\tRET")
+}
+
+func zeroARM64(w io.Writer) {
+	// ZR: always zero
+	// R16 (aka REGRT1): ptr to memory to be zeroed - 8
+	// On return, R16 points to the last zeroed dword.
+	fmt.Fprintln(w, "TEXT runtime·duffzero(SB), NOSPLIT, $-8-0")
+	for i := 0; i < 128; i++ {
+		fmt.Fprintln(w, "\tMOVD.W\tZR, 8(R16)")
+	}
+	fmt.Fprintln(w, "\tRET")
+}
+
+func copyARM64(w io.Writer) {
+	fmt.Fprintln(w, "// TODO: Implement runtime·duffcopy.")
+}
+
+func tagsPPC64x(w io.Writer) {
+	fmt.Fprintln(w)
+	fmt.Fprintln(w, "// +build ppc64 ppc64le")
+	fmt.Fprintln(w)
+}
+
+func zeroPPC64x(w io.Writer) {
+	// R0: always zero
+	// R3 (aka REGRT1): ptr to memory to be zeroed - 8
+	// On return, R3 points to the last zeroed dword.
+	fmt.Fprintln(w, "TEXT runtime·duffzero(SB), NOSPLIT, $-8-0")
+	for i := 0; i < 128; i++ {
+		fmt.Fprintln(w, "\tMOVDU\tR0, 8(R3)")
+	}
+	fmt.Fprintln(w, "\tRETURN")
+}
+
+func copyPPC64x(w io.Writer) {
+	fmt.Fprintln(w, "// TODO: Implement runtime·duffcopy.")
+}