mem-cache: Implement a zero compressor

The zero compressor can only compress data composed solely of zero
bits.

Change-Id: I8b359c03776a8748abd144a178bda944b5a1b766
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/21155
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>

4 files changed, 212 insertions, 0 deletions

diff --git a/src/mem/cache/compressors/Compressors.py b/src/mem/cache/compressors/Compressors.py
index 4db6d4316..a8e51a577 100644
--- a/src/mem/cache/compressors/Compressors.py
+++ b/src/mem/cache/compressors/Compressors.py
@@ -68,3 +68,8 @@ class FPCD(BaseDictionaryCompressor):
     cxx_header = "mem/cache/compressors/fpcd.hh"
 
     dictionary_size = 2
+
+class ZeroCompressor(BaseDictionaryCompressor):
+    type = 'ZeroCompressor'
+    cxx_class = 'ZeroCompressor'
+    cxx_header = "mem/cache/compressors/zero.hh"
diff --git a/src/mem/cache/compressors/SConscript b/src/mem/cache/compressors/SConscript
index 4df20d2a3..27d852dbc 100644
--- a/src/mem/cache/compressors/SConscript
+++ b/src/mem/cache/compressors/SConscript
@@ -37,3 +37,4 @@ Source('base_dictionary_compressor.cc')
 Source('bdi.cc')
 Source('cpack.cc')
 Source('fpcd.cc')
+Source('zero.cc')
diff --git a/src/mem/cache/compressors/zero.cc b/src/mem/cache/compressors/zero.cc
new file mode 100644
index 000000000..3fdf5f1e8
--- /dev/null
+++ b/src/mem/cache/compressors/zero.cc
@@ -0,0 +1,81 @@
+/*
+ * Copyright (c) 2019 Inria
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met: redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer;
+ * redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution;
+ * neither the name of the copyright holders nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * Authors: Daniel Carvalho
+ */
+
+/** @file
+ * Implementation of a zero compressor, which compressed data if it is entirely
+ * composed of zero bits.
+ */
+
+#include "mem/cache/compressors/zero.hh"
+
+#include "debug/CacheComp.hh"
+#include "mem/cache/compressors/dictionary_compressor_impl.hh"
+#include "params/ZeroCompressor.hh"
+
+ZeroCompressor::ZeroCompressor(const Params *p)
+    : DictionaryCompressor<uint64_t>(p)
+{
+}
+
+void
+ZeroCompressor::addToDictionary(DictionaryEntry data)
+{
+    assert(numEntries < dictionarySize);
+    dictionary[numEntries++] = data;
+}
+
+std::unique_ptr<BaseCacheCompressor::CompressionData>
+ZeroCompressor::compress(const uint64_t* data, Cycles& comp_lat,
+    Cycles& decomp_lat)
+{
+    std::unique_ptr<BaseCacheCompressor::CompressionData> comp_data =
+        DictionaryCompressor::compress(data);
+
+    // If there is any non-zero entry, the compressor failed
+    if (numEntries > 0) {
+        comp_data->setSizeBits(blkSize * 8);
+        DPRINTF(CacheComp, "Zero compression failed\n");
+    }
+
+    // Set compression latency (Assumes full line zero comparison)
+    comp_lat = Cycles(1);
+
+    // Set decompression latency
+    decomp_lat = Cycles(1);
+
+    // Return compressed line
+    return comp_data;
+}
+
+ZeroCompressor*
+ZeroCompressorParams::create()
+{
+    return new ZeroCompressor(this);
+}
diff --git a/src/mem/cache/compressors/zero.hh b/src/mem/cache/compressors/zero.hh
new file mode 100644
index 000000000..62b363349
--- /dev/null
+++ b/src/mem/cache/compressors/zero.hh
@@ -0,0 +1,125 @@
+/*
+ * Copyright (c) 2019 Inria
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met: redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer;
+ * redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution;
+ * neither the name of the copyright holders nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * Authors: Daniel Carvalho
+ */
+
+/** @file
+ * Definition of a zero compressor, which compressed data if it is entirely
+ * composed of zero bits.
+ */
+
+#ifndef __MEM_CACHE_COMPRESSORS_ZERO_HH__
+#define __MEM_CACHE_COMPRESSORS_ZERO_HH__
+
+#include <array>
+#include <cstdint>
+#include <map>
+#include <memory>
+
+#include "mem/cache/compressors/dictionary_compressor.hh"
+
+struct ZeroCompressorParams;
+
+class ZeroCompressor : public DictionaryCompressor<uint64_t>
+{
+  protected:
+    using DictionaryEntry = DictionaryCompressor<uint64_t>::DictionaryEntry;
+
+    // Forward declaration of all possible patterns
+    class PatternX;
+    class PatternZ;
+
+    /**
+     * The patterns proposed in the paper. Each letter represents a byte:
+     * Z is a null byte, M is a dictionary match, X is a new value.
+     * These are used as indexes to reference the pattern data. If a new
+     * pattern is added, it must be done before NUM_PATTERNS.
+     */
+    typedef enum {
+        X, Z, NUM_PATTERNS
+    } PatternNumber;
+
+    /**
+     * Convenience factory declaration. The templates must be organized by
+     * size, with the smallest first, and "no-match" last.
+     */
+    using PatternFactory = Factory<PatternZ, PatternX>;
+
+    uint64_t getNumPatterns() const override { return NUM_PATTERNS; }
+
+    std::string
+    getName(int number) const override
+    {
+        static std::map<int, std::string> pattern_names = {
+            {X, "X"}, {Z, "Z"}
+        };
+
+        return pattern_names[number];
+    };
+
+    std::unique_ptr<Pattern>
+    getPattern(const DictionaryEntry& bytes, const DictionaryEntry& dict_bytes,
+        const int match_location) const override
+    {
+        return PatternFactory::getPattern(bytes, dict_bytes, match_location);
+    }
+
+    void addToDictionary(DictionaryEntry data) override;
+
+    std::unique_ptr<BaseCacheCompressor::CompressionData> compress(
+        const uint64_t* data, Cycles& comp_lat, Cycles& decomp_lat) override;
+
+  public:
+    typedef ZeroCompressorParams Params;
+    ZeroCompressor(const Params *p);
+    ~ZeroCompressor() = default;
+};
+
+class ZeroCompressor::PatternX
+    : public DictionaryCompressor::UncompressedPattern
+{
+  public:
+    PatternX(const DictionaryEntry bytes, const int match_location)
+        : DictionaryCompressor::UncompressedPattern(X, 0, 1, match_location,
+          bytes)
+    {
+    }
+};
+
+class ZeroCompressor::PatternZ
+    : public DictionaryCompressor::MaskedValuePattern<0, 0xFFFFFFFFFFFFFFFF>
+{
+  public:
+    PatternZ(const DictionaryEntry bytes, const int match_location)
+        : DictionaryCompressor::MaskedValuePattern<0, 0xFFFFFFFFFFFFFFFF>(
+          Z, 1, 1, match_location, bytes)
+    {
+    }
+};
+
+#endif //__MEM_CACHE_COMPRESSORS_ZERO_HH__