[SharedCache] Optimize `ReadExportNode`

`ReadExportNode` is called a lot during the initial load of the shared
cache and thus impacts how long it takes for the UI to become
responsive. This is a collection of optimizations that cut the time
spent within `ReadExportNode` by 50%:

1. Pass iterators to `ReadExportNode` rather than a `DataBuffer` + offset.
   The lack of inlining in `DataBuffer`'s `operator[]` kills performance.
   Ideally this would have used `std::span`, but that would require
   bumping the minimum C++ version to C++20.
2. Add `MMappedFileAccessor::ReadSpan` so that `ReadExportNode` can
   operate directly on the mapped data without first copying it.
3. Removes a call to `GetAnalysisFunctionsForAddress` whose result was
   unused.
4. Use `std::find` to find the nul at the end of strings rather than
   assembling the string a character at a time. This avoids repeatedly
   growing the string.
5. Avoid the usual `Symbol` constructor in favor of `BNCreateSymbol`.
   The `Symbol` constructor has over head in two forms:
   1. It has a `NameSpace` as an argument. Creating / destroying this
      allocates and deallocates memory We could create a single
      instance and reuse it for all calls, but...
   2. The constructor copies all fields of the `NameSpace` to the heap
      before calling `BNCreateSymbol` and then deallocates them
      afterwards. This seems unnecessary, and adds a non-trivial amount
      of overhead.

   This can go back to directly constructing the `Symbol` once the
   constructors are improved.

1 files changed, 8 insertions, 0 deletions

diff --git a/view/sharedcache/core/VM.h b/view/sharedcache/core/VM.h
index 955dcbec..d567dce8 100644
--- a/view/sharedcache/core/VM.h
+++ b/view/sharedcache/core/VM.h
@@ -187,6 +187,14 @@ public:
 
     BinaryNinja::DataBuffer ReadBuffer(size_t addr, size_t length);
 
+    // Returns a range of pointers within the mapped memory region corresponding to
+    // {addr, length}.
+    // WARNING: The pointers returned by this method is only valid for the lifetime
+    // of this file accessor.
+    // TODO: This should use std::span<const uint8_t> once the minimum supported
+    // C++ version supports it.
+    std::pair<const uint8_t*, const uint8_t*> ReadSpan(size_t addr, size_t length);
+
     void Read(void *dest, size_t addr, size_t length);
 };