compress/flate: remove compressor.hash field

After CL 20929, the only remaining uses of d.hash are immediately
after it is set.

Benchmarks where benchstat reports a non-zero delta:

name                              old time/op    new time/op    delta
Decode/Newton/Huffman/1e5-12         982µs ± 6%     922µs ± 4%  -6.12%  (p=0.000 n=10+10)
Decode/Newton/Huffman/1e6-12        8.14ms ± 2%    7.71ms ± 2%  -5.19%  (p=0.000 n=10+10)
Encode/Digits/Huffman/1e5-12         241µs ± 0%     239µs ± 0%  -0.62%  (p=0.000 n=9+10)
Encode/Digits/Speed/1e4-12           113µs ± 0%     114µs ± 0%  +1.21%  (p=0.000 n=9+8)
Encode/Digits/Speed/1e5-12          1.04ms ± 0%    1.05ms ± 0%  +0.22%  (p=0.027 n=9+8)
Encode/Digits/Speed/1e6-12          10.3ms ± 0%    10.3ms ± 0%  +0.16%  (p=0.036 n=9+8)
Encode/Digits/Default/1e4-12         193µs ± 0%     195µs ± 1%  +0.77%  (p=0.010 n=8+8)
Encode/Digits/Default/1e5-12        2.92ms ± 1%    2.93ms ± 0%  +0.54%  (p=0.002 n=8+8)
Encode/Digits/Compression/1e4-12     193µs ± 0%     194µs ± 0%  +0.67%  (p=0.000 n=8+8)
Encode/Digits/Compression/1e5-12    2.92ms ± 0%    2.93ms ± 0%  +0.53%  (p=0.002 n=8+8)
Encode/Digits/Compression/1e6-12    31.0ms ± 1%    31.2ms ± 0%  +0.80%  (p=0.000 n=10+9)
Encode/Newton/Huffman/1e4-12        34.8µs ± 1%    34.3µs ± 0%  -1.31%  (p=0.000 n=9+10)
Encode/Newton/Huffman/1e5-12         294µs ± 0%     291µs ± 0%  -1.09%  (p=0.000 n=8+9)
Encode/Newton/Huffman/1e6-12        2.91ms ± 0%    2.89ms ± 0%  -0.89%  (p=0.000 n=8+9)
Encode/Newton/Speed/1e5-12           838µs ± 0%     836µs ± 0%  -0.18%  (p=0.015 n=8+8)
Encode/Newton/Speed/1e6-12          8.35ms ± 0%    8.28ms ± 1%  -0.89%  (p=0.000 n=8+10)
Encode/Newton/Default/1e5-12        3.55ms ± 0%    3.54ms ± 0%  -0.23%  (p=0.027 n=8+9)
Encode/Newton/Default/1e6-12        37.4ms ± 0%    37.3ms ± 0%  -0.18%  (p=0.001 n=9+8)
Encode/Newton/Compression/1e6-12    53.3ms ± 0%    53.1ms ± 0%  -0.25%  (p=0.010 n=10+9)

name                              old speed      new speed      delta
Decode/Newton/Huffman/1e5-12       102MB/s ± 6%   109MB/s ± 4%  +6.48%  (p=0.000 n=10+10)
Decode/Newton/Huffman/1e6-12       123MB/s ± 2%   130MB/s ± 2%  +5.49%  (p=0.000 n=10+10)
Encode/Digits/Huffman/1e5-12       416MB/s ± 0%   418MB/s ± 0%  +0.62%  (p=0.000 n=9+10)
Encode/Digits/Speed/1e4-12        88.9MB/s ± 0%  87.8MB/s ± 0%  -1.19%  (p=0.000 n=9+8)
Encode/Digits/Speed/1e5-12        95.7MB/s ± 0%  95.5MB/s ± 0%  -0.22%  (p=0.025 n=9+8)
Encode/Digits/Speed/1e6-12        97.5MB/s ± 0%  97.3MB/s ± 0%  -0.16%  (p=0.026 n=9+8)
Encode/Digits/Default/1e4-12      51.7MB/s ± 0%  51.3MB/s ± 1%  -0.76%  (p=0.007 n=8+8)
Encode/Digits/Default/1e5-12      34.3MB/s ± 1%  34.1MB/s ± 0%  -0.54%  (p=0.001 n=8+8)
Encode/Digits/Compression/1e4-12  51.8MB/s ± 0%  51.5MB/s ± 0%  -0.66%  (p=0.000 n=8+8)
Encode/Digits/Compression/1e5-12  34.3MB/s ± 0%  34.1MB/s ± 0%  -0.53%  (p=0.002 n=8+8)
Encode/Digits/Compression/1e6-12  32.3MB/s ± 1%  32.0MB/s ± 0%  -0.79%  (p=0.000 n=10+9)
Encode/Newton/Huffman/1e4-12       288MB/s ± 1%   291MB/s ± 0%  +1.33%  (p=0.000 n=9+10)
Encode/Newton/Huffman/1e5-12       340MB/s ± 0%   344MB/s ± 0%  +1.10%  (p=0.000 n=8+9)
Encode/Newton/Huffman/1e6-12       343MB/s ± 0%   346MB/s ± 0%  +0.90%  (p=0.000 n=8+9)
Encode/Newton/Speed/1e5-12         119MB/s ± 0%   120MB/s ± 0%  +0.18%  (p=0.014 n=8+8)
Encode/Newton/Speed/1e6-12         120MB/s ± 0%   121MB/s ± 1%  +0.90%  (p=0.000 n=8+10)
Encode/Newton/Default/1e5-12      28.2MB/s ± 0%  28.3MB/s ± 0%  +0.23%  (p=0.029 n=8+9)
Encode/Newton/Default/1e6-12      26.7MB/s ± 0%  26.8MB/s ± 0%  +0.20%  (p=0.000 n=9+7)
Encode/Newton/Compression/1e6-12  18.8MB/s ± 0%  18.8MB/s ± 0%  +0.25%  (p=0.012 n=10+9)

Change-Id: I8ba0efcf5d42595d856082656b45f87bb3d7be0f
Reviewed-on: https://go-review.googlesource.com/c/go/+/404696
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Joseph Tsai <joetsai@digital-static.net>
Run-TryBot: Ian Lance Taylor <iant@google.com>

Author: ianlancetaylor

src/compress/flate/deflate.go

@@ -113,7 +113,6 @@ type compressor struct {
 	// deflate state
 	length         int
 	offset         int
-	hash           uint32
 	maxInsertIndex int
 	err            error
 
@@ -222,7 +221,6 @@ func (d *compressor) fillWindow(b []byte) {
 			// Set the head of the hash chain to us.
 			*hh = uint32(di + d.hashOffset)
 		}
-		d.hash = newH
 	}
 	// Update window information.
 	d.windowEnd = n
@@ -377,7 +375,6 @@ func (d *compressor) initDeflate() {
 	d.offset = 0
 	d.byteAvailable = false
 	d.index = 0
-	d.hash = 0
 	d.chainHead = -1
 	d.bulkHasher = bulkHash4
 }
@@ -388,9 +385,6 @@ func (d *compressor) deflate() {
 	}
 
 	d.maxInsertIndex = d.windowEnd - (minMatchLength - 1)
-	if d.index < d.maxInsertIndex {
-		d.hash = hash4(d.window[d.index : d.index+minMatchLength])
-	}
 
 Loop:
 	for {
@@ -423,8 +417,8 @@ Loop:
 		}
 		if d.index < d.maxInsertIndex {
 			// Update the hash
-			d.hash = hash4(d.window[d.index : d.index+minMatchLength])
-			hh := &d.hashHead[d.hash&hashMask]
+			hash := hash4(d.window[d.index : d.index+minMatchLength])
+			hh := &d.hashHead[hash&hashMask]
 			d.chainHead = int(*hh)
 			d.hashPrev[d.index&windowMask] = uint32(d.chainHead)
 			*hh = uint32(d.index + d.hashOffset)
@@ -469,10 +463,10 @@ Loop:
 				index := d.index
 				for index++; index < newIndex; index++ {
 					if index < d.maxInsertIndex {
-						d.hash = hash4(d.window[index : index+minMatchLength])
+						hash := hash4(d.window[index : index+minMatchLength])
 						// Get previous value with the same hash.
 						// Our chain should point to the previous value.
-						hh := &d.hashHead[d.hash&hashMask]
+						hh := &d.hashHead[hash&hashMask]
 						d.hashPrev[index&windowMask] = *hh
 						// Set the head of the hash chain to us.
 						*hh = uint32(index + d.hashOffset)
@@ -488,9 +482,6 @@ Loop:
 				// For matches this long, we don't bother inserting each individual
 				// item into the table.
 				d.index += d.length
-				if d.index < d.maxInsertIndex {
-					d.hash = hash4(d.window[d.index : d.index+minMatchLength])
-				}
 			}
 			if len(d.tokens) == maxFlateBlockTokens {
 				// The block includes the current character
@@ -634,7 +625,6 @@ func (d *compressor) reset(w io.Writer) {
 		d.tokens = d.tokens[:0]
 		d.length = minMatchLength - 1
 		d.offset = 0
-		d.hash = 0
 		d.maxInsertIndex = 0
 	}
 }