llvm-dwp: Add an abstraction for the DWP string pool

Also reference strings in the memory mapped file, reduces memory usage
on a large test case by 18.5%.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@270449 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 54 insertions, 0 deletions

diff --git a/tools/llvm-dwp/DWPStringPool.h b/tools/llvm-dwp/DWPStringPool.h
new file mode 100644
index 00000000000..8923e4c426e
--- /dev/null
+++ b/tools/llvm-dwp/DWPStringPool.h
@@ -0,0 +1,54 @@
+#ifndef TOOLS_LLVM_DWP_DWPSTRINGPOOL
+#define TOOLS_LLVM_DWP_DWPSTRINGPOOL
+
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/MC/MCSection.h"
+#include "llvm/MC/MCStreamer.h"
+#include <cassert>
+
+class DWPStringPool {
+
+  struct CStrDenseMapInfo {
+    static inline const char *getEmptyKey() {
+      return reinterpret_cast<const char *>(~static_cast<uintptr_t>(0));
+    }
+    static inline const char *getTombstoneKey() {
+      return reinterpret_cast<const char *>(~static_cast<uintptr_t>(1));
+    }
+    static unsigned getHashValue(const char *Val) {
+      assert(Val != getEmptyKey() && "Cannot hash the empty key!");
+      assert(Val != getTombstoneKey() && "Cannot hash the tombstone key!");
+      return (unsigned)hash_value(StringRef(Val));
+    }
+    static bool isEqual(const char *LHS, const char *RHS) {
+      if (RHS == getEmptyKey())
+        return LHS == getEmptyKey();
+      if (RHS == getTombstoneKey())
+        return LHS == getTombstoneKey();
+      return strcmp(LHS, RHS) == 0;
+    }
+  };
+
+  MCStreamer &Out;
+  MCSection *Sec;
+  DenseMap<const char *, uint32_t, CStrDenseMapInfo> Pool;
+  uint32_t Offset = 0;
+
+public:
+  DWPStringPool(MCStreamer &Out, MCSection *Sec) : Out(Out), Sec(Sec) {}
+
+  uint32_t getOffset(const char *Str, unsigned Length) {
+    assert(strlen(Str) + 1 == Length && "Ensure length hint is correct");
+
+    auto Pair = Pool.insert(std::make_pair(Str, Offset));
+    if (Pair.second) {
+      Out.SwitchSection(Sec);
+      Out.EmitBytes(StringRef(Str, Length));
+      Offset += Length;
+    }
+
+    return Pair.first->second;
+  }
+};
+
+#endif