[clang] [llvm] [HIP] change compress level (PR #83605)

[Fangrui Song via cfe-commits]

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@@ -942,20 +942,28 @@ CompressedOffloadBundle::compress(const llvm::MemoryBuffer &Input,
       Input.getBuffer().size());
 
   llvm::compression::Format CompressionFormat;
+  int Level;
 
-  if (llvm::compression::zstd::isAvailable())
+  if (llvm::compression::zstd::isAvailable()) {
     CompressionFormat = llvm::compression::Format::Zstd;
-  else if (llvm::compression::zlib::isAvailable())
+    // Use a high zstd compress level by default for better size reduction.
+    const int DefaultZstdLevel = 20;
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MaskRay wrote:

High levels decrease compression speed substantially. Have you checked that 20 hits a good sweet spot between 9 to 22 (max)?

Is OffloadBundler used more like a linker than a compile action where parallelism helps? If yes, lld/ELF/OutputSections.cpp has some code, which can be copied here. (Please don't share the code, I think some duplication in lld/ELF makes lld code easier to change)

https://github.com/llvm/llvm-project/pull/83605