From 19df4e94ee4f2323e5fe1b915f7e81a6034cfc56 Mon Sep 17 00:00:00 2001
From: Gabe Black <gblack@eecs.umich.edu>
Date: Sat, 26 May 2012 13:45:12 -0700
Subject: ISA,CPU: Generalize and split out the components of the decode cache.

This will allow it to be specialized by the ISAs. The existing caching scheme
is provided by the BasicDecodeCache in the GenericISA namespace and is built
from the generalized components.

--HG--
rename : src/cpu/decode_cache.cc => src/arch/generic/decode_cache.cc
---
 src/cpu/decode_cache.hh | 107 +++++++++++++++++++++++++++++++++---------------
 1 file changed, 73 insertions(+), 34 deletions(-)

(limited to 'src/cpu/decode_cache.hh')

diff --git a/src/cpu/decode_cache.hh b/src/cpu/decode_cache.hh
index 473340586..34387419f 100644
--- a/src/cpu/decode_cache.hh
+++ b/src/cpu/decode_cache.hh
@@ -35,56 +35,95 @@
 #include "arch/types.hh"
 #include "base/hashmap.hh"
 #include "config/the_isa.hh"
-#include "cpu/static_inst.hh"
+#include "cpu/static_inst_fwd.hh"
 
 namespace TheISA
 {
     class Decoder;
 }
 
-class DecodeCache
+namespace DecodeCache
 {
-  private:
-    typedef TheISA::ExtMachInst ExtMachInst;
 
-    /// Hash of decoded instructions.
-    typedef m5::hash_map<ExtMachInst, StaticInstPtr> InstMap;
-    InstMap instMap;
-    struct DecodePage {
-        StaticInstPtr insts[TheISA::PageBytes];
+/// Hash for decoded instructions.
+typedef m5::hash_map<TheISA::ExtMachInst, StaticInstPtr> InstMap;
+
+/// A sparse map from an Addr to a Value, stored in page chunks.
+template<class Value>
+class AddrMap
+{
+  protected:
+    // A pages worth of cache entries.
+    struct CachePage {
+        Value items[TheISA::PageBytes];
     };
+    // A map of cache pages which allows a sparse mapping.
+    typedef typename m5::hash_map<Addr, CachePage *> PageMap;
+    typedef typename PageMap::iterator PageIt;
+    // Mini cache of recent lookups.
+    PageIt recent[2];
+    PageMap pageMap;
+
+    /// Update the mini cache of recent lookups.
+    /// @param recentest The most recent result;
+    void
+    update(PageIt recentest)
+    {
+        recent[1] = recent[0];
+        recent[0] = recentest;
+    }
 
-    /// A store of DecodePages. Basically a slightly smarter hash_map.
-    class DecodePages
+    /// Attempt to find the CacheePage which goes with a particular
+    /// address. First check the small cache of recent results, then
+    /// actually look in the hash_map.
+    /// @param addr The address to look up.
+    CachePage *
+    getPage(Addr addr)
     {
-      protected:
-        typedef typename m5::hash_map<Addr, DecodePage *> PageMap;
-        typedef typename PageMap::iterator PageIt;
-        PageIt recent[2];
-        PageMap pageMap;
+        Addr page_addr = addr & ~(TheISA::PageBytes - 1);
 
-        /// Update the small cache of recent lookups.
-        /// @param recentest The most recent result;
-        void update(PageIt recentest);
-        void addPage(Addr addr, DecodePage *page);
+        // Check against recent lookups.
+        if (recent[0] != pageMap.end()) {
+            if (recent[0]->first == page_addr)
+                return recent[0]->second;
+            if (recent[1] != pageMap.end() &&
+                    recent[1]->first == page_addr) {
+                update(recent[1]);
+                // recent[1] has just become recent[0].
+                return recent[0]->second;
+            }
+        }
 
-      public:
-        /// Constructor
-        DecodePages();
+        // Actually look in the has_map.
+        PageIt it = pageMap.find(page_addr);
+        if (it != pageMap.end()) {
+            update(it);
+            return it->second;
+        }
 
-        /// Attempt to find the DecodePage which goes with a particular
-        /// address. First check the small cache of recent results, then
-        /// actually look in the hash_map.
-        /// @param addr The address to look up.
-        DecodePage *getPage(Addr addr);
-    } decodePages;
+        // Didn't find an existing page, so add a new one.
+        CachePage *newPage = new CachePage;
+        page_addr = page_addr & ~(TheISA::PageBytes - 1);
+        typename PageMap::value_type to_insert(page_addr, newPage);
+        update(pageMap.insert(to_insert).first);
+        return newPage;
+    }
 
   public:
-    /// Decode a machine instruction.
-    /// @param mach_inst The binary instruction to decode.
-    /// @retval A pointer to the corresponding StaticInst object.
-    StaticInstPtr decode(TheISA::Decoder * const decoder,
-            ExtMachInst mach_inst, Addr addr);
+    /// Constructor
+    AddrMap()
+    {
+        recent[0] = recent[1] = pageMap.end();
+    }
+
+    Value &
+    lookup(Addr addr)
+    {
+        CachePage *page = getPage(addr);
+        return page->items[addr & (TheISA::PageBytes - 1)];
+    }
 };
 
+} // namespace DecodeCache
+
 #endif // __CPU_DECODE_CACHE_HH__
-- 
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