[llvm-branch-commits] [llvm-objcopy] Simplify --[de]compress-debug-sections and don't compress SHF_ALLOC sections (PR #84885)

[Fangrui Song via llvm-branch-commits]

================
@@ -214,33 +214,34 @@ static Error dumpSectionToFile(StringRef SecName, StringRef Filename,
                            SecName.str().c_str());
 }
 
-static bool isCompressable(const SectionBase &Sec) {
-  return !(Sec.Flags & ELF::SHF_COMPRESSED) &&
-         StringRef(Sec.Name).starts_with(".debug");
-}
-
-static Error replaceDebugSections(
-    Object &Obj, function_ref<bool(const SectionBase &)> ShouldReplace,
-    function_ref<Expected<SectionBase *>(const SectionBase *)> AddSection) {
+Error Object::compressOrDecompressSections(const CommonConfig &Config) {
   // Build a list of the debug sections we are going to replace.
   // We can't call `AddSection` while iterating over sections,
   // because it would mutate the sections array.
-  SmallVector<SectionBase *, 13> ToReplace;
-  for (auto &Sec : Obj.sections())
-    if (ShouldReplace(Sec))
-      ToReplace.push_back(&Sec);
-
-  // Build a mapping from original section to a new one.
-  DenseMap<SectionBase *, SectionBase *> FromTo;
-  for (SectionBase *S : ToReplace) {
-    Expected<SectionBase *> NewSection = AddSection(S);
-    if (!NewSection)
-      return NewSection.takeError();
-
-    FromTo[S] = *NewSection;
+  SmallVector<std::pair<SectionBase *, std::function<SectionBase *()>>, 0>
----------------
MaskRay wrote:

The default is a smart value to keep `sizeof(SmallVector<T>)` around 64 bytes. Someone might send a RFC to change the default to 0 and have another mechanism to use the default. I believe `, 0` is used much more than the smart default, since in many cases people don't care about extra heap allocations at runtime, but I care about code size and the smaller structure of `SmallVector`.

https://github.com/llvm/llvm-project/pull/84885