s2: Don't use stack for index tables (#1014)

* s2: Don't use stack for index tables

Provide a pooled array pointer for tables instead of using stack.

Seems like Go is still unstable with large stacks, so use alternative method.

s2/_generate/gen.go

@@ -81,7 +81,7 @@ func main() {
 	o.maxSkip = 100
 	o.genEncodeBetterBlockAsm("encodeSnappyBetterBlockAsm", 17, 14, 7, 7, limit14B)
 	o.maxSkip = 0
-	o.genEncodeBetterBlockAsm("encodeSnappyBetterBlockAsm64K", 16, 14, 7, 7, 64<<10-1)
+	o.genEncodeBetterBlockAsm("encodeSnappyBetterBlockAsm64K", 16, 13, 7, 7, 64<<10-1)
 	o.genEncodeBetterBlockAsm("encodeSnappyBetterBlockAsm12B", 14, 12, 6, 6, limit12B)
 	o.genEncodeBetterBlockAsm("encodeSnappyBetterBlockAsm10B", 12, 10, 5, 6, limit10B)
 	o.genEncodeBetterBlockAsm("encodeSnappyBetterBlockAsm8B", 10, 8, 4, 6, limit8B)
@@ -146,6 +146,15 @@ func assert(fn func(ok LabelRef)) {
 	}
 }
 
+type regTable struct {
+	r    reg.Register
+	disp int
+}
+
+func (r regTable) Idx(idx reg.GPVirtual, scale uint8) Mem {
+	return Mem{Base: r.r, Index: idx, Scale: scale, Disp: r.disp}
+}
+
 type options struct {
 	snappy       bool
 	bmi1         bool
@@ -163,7 +172,15 @@ func (o options) genEncodeBlockAsm(name string, tableBits, skipLog, hashBytes, m
 	if o.skipOutput {
 		dstTxt = ""
 	}
-	TEXT(name, 0, "func("+dstTxt+"src []byte) int")
+
+	var tableSize = 4 * (1 << tableBits)
+	// Memzero needs at least 128 bytes.
+	if tableSize < 128 {
+		panic("tableSize must be at least 128 bytes")
+	}
+
+	arrPtr := fmt.Sprintf(",tmp *[%d]byte", tableSize)
+	TEXT(name, 0, "func("+dstTxt+"src []byte"+arrPtr+") int")
 	Doc(name+" encodes a non-empty src to a guaranteed-large-enough dst.",
 		fmt.Sprintf("Maximum input %d bytes.", maxLen),
 		"It assumes that the varint-encoded length of the decompressed bytes has already been written.", "")
@@ -173,7 +190,6 @@ func (o options) genEncodeBlockAsm(name string, tableBits, skipLog, hashBytes, m
 	o.maxOffset = maxLen - 1
 	var literalMaxOverhead = maxLitOverheadFor(maxLen)
 
-	var tableSize = 4 * (1 << tableBits)
 	// Memzero needs at least 128 bytes.
 	if tableSize < 128 {
 		panic("tableSize must be at least 128 bytes")
@@ -209,8 +225,8 @@ func (o options) genEncodeBlockAsm(name string, tableBits, skipLog, hashBytes, m
 	// nextSTempL keeps nextS while other functions are being called.
 	nextSTempL := AllocLocal(4)
 
-	// Alloc table last
-	table := AllocLocal(tableSize)
+	// Load pointer to temp table
+	table := regTable{r: Load(Param("tmp"), GP64())}
 
 	dst := GP64()
 	if !o.skipOutput {
@@ -236,7 +252,7 @@ func (o options) genEncodeBlockAsm(name string, tableBits, skipLog, hashBytes, m
 		iReg := GP64()
 		MOVQ(U32(tableSize/8/16), iReg)
 		tablePtr := GP64()
-		LEAQ(table, tablePtr)
+		MOVQ(table.r, tablePtr)
 		zeroXmm := XMM()
 		PXOR(zeroXmm, zeroXmm)
 
@@ -855,7 +871,17 @@ func maxLitOverheadFor(n int) int {
 }
 
 func (o options) genEncodeBetterBlockAsm(name string, lTableBits, sTableBits, skipLog, lHashBytes, maxLen int) {
-	TEXT(name, 0, "func(dst, src []byte) int")
+	var lTableSize = 4 * (1 << lTableBits)
+	var sTableSize = 4 * (1 << sTableBits)
+	tableSize := lTableSize + sTableSize
+
+	// Memzero needs at least 128 bytes.
+	if tableSize < 128 {
+		panic("tableSize must be at least 128 bytes")
+	}
+	arrPtr := fmt.Sprintf(", tmp *[%d]byte", tableSize)
+
+	TEXT(name, 0, "func(dst, src []byte"+arrPtr+") int")
 	Doc(name+" encodes a non-empty src to a guaranteed-large-enough dst.",
 		fmt.Sprintf("Maximum input %d bytes.", maxLen),
 		"It assumes that the varint-encoded length of the decompressed bytes has already been written.", "")
@@ -870,9 +896,6 @@ func (o options) genEncodeBetterBlockAsm(name string, lTableBits, sTableBits, sk
 	o.maxLen = maxLen
 	o.maxOffset = maxLen - 1
 
-	var lTableSize = 4 * (1 << lTableBits)
-	var sTableSize = 4 * (1 << sTableBits)
-
 	// Memzero needs at least 128 bytes.
 	if (lTableSize + sTableSize) < 128 {
 		panic("tableSize must be at least 128 bytes")
@@ -905,9 +928,9 @@ func (o options) genEncodeBetterBlockAsm(name string, lTableBits, sTableBits, sk
 	// nextSTempL keeps nextS while other functions are being called.
 	nextSTempL := AllocLocal(4)
 
-	// Alloc table last, lTab must be before sTab.
-	lTab := AllocLocal(lTableSize)
-	sTab := AllocLocal(sTableSize)
+	table := Load(Param("tmp"), GP64())
+	lTab := regTable{r: table}
+	sTab := regTable{r: table, disp: lTableSize}
 
 	dst := GP64()
 	{
@@ -930,7 +953,7 @@ func (o options) genEncodeBetterBlockAsm(name string, lTableBits, sTableBits, sk
 		iReg := GP64()
 		MOVQ(U32((sTableSize+lTableSize)/8/16), iReg)
 		tablePtr := GP64()
-		LEAQ(lTab, tablePtr)
+		MOVQ(table, tablePtr)
 		zeroXmm := XMM()
 		PXOR(zeroXmm, zeroXmm)
 
@@ -2916,7 +2939,7 @@ func (o options) cvtLZ4BlockAsm(lz4s bool) {
 	TEXT("cvt"+srcAlgo+"Block"+snap, NOSPLIT, "func(dst, src []byte) (uncompressed int, dstUsed int)")
 	Doc("cvt"+srcAlgo+"Block converts an "+srcAlgo+" block to "+dstAlgo, "")
 	Pragma("noescape")
-	o.outputMargin = 10
+	o.outputMargin = 8
 	o.maxOffset = math.MaxUint16
 
 	const (

s2/encode.go

@@ -9,6 +9,9 @@ import (
 	"encoding/binary"
 	"math"
 	"math/bits"
+	"sync"
+
+	"github.com/klauspost/compress/internal/race"
 )
 
 // Encode returns the encoded form of src. The returned slice may be a sub-
@@ -52,6 +55,8 @@ func Encode(dst, src []byte) []byte {
 	return dst[:d]
 }
 
+var estblockPool [2]sync.Pool
+
 // EstimateBlockSize will perform a very fast compression
 // without outputting the result and return the compressed output size.
 // The function returns -1 if no improvement could be achieved.
@@ -61,9 +66,25 @@ func EstimateBlockSize(src []byte) (d int) {
 		return -1
 	}
 	if len(src) <= 1024 {
-		d = calcBlockSizeSmall(src)
+		const sz, pool = 2048, 0
+		tmp, ok := estblockPool[pool].Get().(*[sz]byte)
+		if !ok {
+			tmp = &[sz]byte{}
+		}
+		race.WriteSlice(tmp[:])
+		defer estblockPool[pool].Put(tmp)
+
+		d = calcBlockSizeSmall(src, tmp)
 	} else {
-		d = calcBlockSize(src)
+		const sz, pool = 32768, 1
+		tmp, ok := estblockPool[pool].Get().(*[sz]byte)
+		if !ok {
+			tmp = &[sz]byte{}
+		}
+		race.WriteSlice(tmp[:])
+		defer estblockPool[pool].Put(tmp)
+
+		d = calcBlockSize(src, tmp)
 	}
 
 	if d == 0 {