[Lldb-commits] [clang] [clang-tools-extra] [lld] [lldb] [llvm] Rework the `Option` library to reduce dynamic relocations (PR #119198)

[Chandler Carruth via lldb-commits]

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@@ -80,15 +78,56 @@ class OptTable {
     const char *AliasArgs;
     const char *Values;
 
-    StringRef getName() const {
-      unsigned PrefixLength = Prefixes.empty() ? 0 : Prefixes[0].size();
-      return PrefixedName.drop_front(PrefixLength);
+    bool hasNoPrefix() const { return PrefixesOffset == 0; }
+
+    unsigned getNumPrefixes(ArrayRef<unsigned> PrefixesTable) const {
+      return PrefixesTable[PrefixesOffset];
+    }
+
+    ArrayRef<unsigned>
+    getPrefixOffsets(ArrayRef<unsigned> PrefixesTable) const {
+      return hasNoPrefix() ? ArrayRef<unsigned>()
+                           : PrefixesTable.slice(PrefixesOffset + 1,
+                                                 getNumPrefixes(PrefixesTable));
+    }
+
+    void appendPrefixes(const char *StrTable, ArrayRef<unsigned> PrefixesTable,
+                        SmallVectorImpl<StringRef> &Prefixes) const {
+      for (unsigned PrefixOffset : getPrefixOffsets(PrefixesTable))
+        Prefixes.push_back(&StrTable[PrefixOffset]);
+    }
+
+    StringRef getPrefix(const char *StrTable, ArrayRef<unsigned> PrefixesTable,
+                        unsigned PrefixIndex) const {
+      return &StrTable[getPrefixOffsets(PrefixesTable)[PrefixIndex]];
+    }
+
+    StringRef getPrefixedName(const char *StrTable) const {
+      return &StrTable[PrefixedNameOffset];
+    }
+
+    StringRef getName(const char *StrTable,
+                      ArrayRef<unsigned> PrefixesTable) const {
+      unsigned PrefixLength =
+          hasNoPrefix() ? 0 : getPrefix(StrTable, PrefixesTable, 0).size();
+      return getPrefixedName(StrTable).drop_front(PrefixLength);
     }
   };
 
 private:
+  // A unified string table for these options. Individual strings are stored as
+  // null terminated C-strings at offsets within this table.
+  const char *StrTable;
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chandlerc wrote:

Happy to use a `StringRef` if folks want here.

I'm not sure about the exact construction though -- I think it'll be annoyingly important that we use something that gets the accelerated implementations of `strlen` when extracting strings from the table. And not sure that `StringRef` has a good tool for doing that in a way that *also* tracks a bound.

But what's your preference about me cutting `StringRef` into the code as-is, versus waiting and coming back through to add a dedicated string table abstraction? Because that would let us have much nicer APIs compared to lifting this into `StringRef`. And it'll have to touch almost exactly the same lines I think.

https://github.com/llvm/llvm-project/pull/119198