[demangler] Fix build breakage

[urnathan]

Summary

D119177 broke some builds.

Let's fix up the header divergence and as algorithm> is a large header, this just open-codes the comparisons.

Also I took the chance to improve the hysteresis. If we needed more than double the buffer, the original code would allocate exactly the amount needed, and thus consequently the next request would also realloc. We're very unlikely to get into wanting more than double, after the first allocation, as it would require the user to have used an identifier larger than the hysteresis. With machine generated code that's possible, but unlikely.

[thakis]

can we keep build fixes separate from behavior changes? :) please split this into two changes.

[urnathan]

Just the fix,

[thakis]

Thanks! lg with "Also I took the chance…" removed from the commit message :)

[urnathan]

fbf7bbcb8399

[ChuanqiXu]

May I ask what's the reason that the previous version would break the build? I am curious since it looks NFC to me.

[urnathan]

In D119951#3328038, @ChuanqiXu wrote:

May I ask what's the reason that the previous version would break the build? I am curious since it looks NFC to me.

I think I flubbed syncing copies after adding <algorithm>, and for some reason that didn;t break my build. As the reporter points out <algorithm>'s rather large for just the one function.

libcxxabi/src/demangle/Utility.h

 // the copy.  See README.txt for more details.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef DEMANGLE_UTILITY_H
 #define DEMANGLE_UTILITY_H
 
 #include "StringView.h"
-#include <algorithm>
 #include <array>
 #include <cstdint>
 #include <cstdlib>
 #include <cstring>
 #include <exception>
 #include <limits>
 
 DEMANGLE_NAMESPACE_BEGIN
 
 // Stream that AST nodes write their string representation into after the AST
 // has been parsed.
 class OutputBuffer {
   char *Buffer = nullptr;
   size_t CurrentPosition = 0;
   size_t BufferCapacity = 0;
 
   // Ensure there are at least N more positions in the buffer.
   void grow(size_t N) {
     size_t Need = N + CurrentPosition;
     if (Need > BufferCapacity) {
       // Avoid many reallocations during startup, with a bit of hysteresis.
       constexpr size_t MinInitAlloc = 1024;
-      Need = std::max(Need, MinInitAlloc);
-      BufferCapacity = std::max(Need, BufferCapacity * 2);
+      if (Need < MinInitAlloc)
+        Need = MinInitAlloc;
+      BufferCapacity *= 2;
+      if (BufferCapacity < Need)
+        BufferCapacity = Need;
       Buffer = static_cast<char *>(std::realloc(Buffer, BufferCapacity));
       if (Buffer == nullptr)
         std::terminate();
     }
   }
 
   OutputBuffer &writeUnsigned(uint64_t N, bool isNeg = false) {
     std::array<char, 21> Temp;

llvm/include/llvm/Demangle/Utility.h

class OutputBuffer {
   size_t BufferCapacity = 0;
 
   // Ensure there are at least N more positions in the buffer.
   void grow(size_t N) {
     size_t Need = N + CurrentPosition;
     if (Need > BufferCapacity) {
       // Avoid many reallocations during startup, with a bit of hysteresis.
       constexpr size_t MinInitAlloc = 1024;
-      Need = std::max(Need, MinInitAlloc);
-      BufferCapacity = std::max(Need, BufferCapacity * 2);
+      if (Need < MinInitAlloc)
+        Need = MinInitAlloc;
+      BufferCapacity *= 2;
+      if (BufferCapacity < Need)
+        BufferCapacity = Need;
       Buffer = static_cast<char *>(std::realloc(Buffer, BufferCapacity));
       if (Buffer == nullptr)
         std::terminate();
     }
   }
 
   OutputBuffer &writeUnsigned(uint64_t N, bool isNeg = false) {
     std::array<char, 21> Temp;