[flang] [llvm] [LLVM-Flang] Improve the realloc size for the write statement (PR #187662)

[Thirumalai Shaktivel via llvm-commits]

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@@ -150,7 +150,19 @@ template <typename STORE, std::size_t minBuffer = 65536> class FileFrame {
     if (bytes > size_) {
       char *old{buffer_};
       auto oldSize{size_};
-      size_ = std::max<std::int64_t>(bytes, size_ + minBuffer);
+      std::int64_t minBuffer_{minBuffer}, newSize{size_ + minBuffer_};
+      // Grow the buffer geometrically. Using larger expansion steps reduces the
+      // number of reallocations and prevents excessive mmap/munmap activity.
+      if (newSize > minBuffer_ * 16) {
+        if (newSize < minBuffer_ * 1024) {
+          // Between 1 MB and 64 MB -> 2×
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Thirumalai-Shaktivel wrote:

Setting the constant value works well. I also checked by changing the default value to 256, and the run was quick.
It seems the problem is with the buffer size. Copying the whole buffer into a new block for every realloc takes time. This fix works. 

I checked different ways of causing any problem, and it works fine. Do you see any issues with checking the constant value?

https://github.com/llvm/llvm-project/pull/187662