[LLD][ELF] Allow multiple thunks to be added for a symbol.

[peter.smith]

Summary

This change permits there to be more than one thunk to be associated with a symbol. For interworking thunks we only require one thunk, but range
extension thunks may require more than one.

[ruiu]

ELF/Relocations.cpp

1059–1060 ↗

(On Diff #101917)

Can you return {ET, false}?

1064 ↗

(On Diff #101917)

If so, you can move the definition of T here.

[peter.smith]

Thanks for the comments. I've updated the diff to return {ET, false} as suggested.

[peter.smith]

Is there anything more I can do to move this patch along?

[peter.smith]

This is patch 2/11 of range thunks. Although it can be independently applied from patch 1.

lld/trunk/ELF/Relocations.h

private:
   void forEachExecInputSection(
       ArrayRef<OutputSectionCommand *> OutputSections,
       std::function<void(OutputSection *, std::vector<InputSection *> *,
                          InputSection *)>
           Fn);
   std::pair<Thunk *, bool> getThunk(SymbolBody &Body, uint32_t Type);
   ThunkSection *addThunkSection(OutputSection *OS,
                                 std::vector<InputSection *> *, uint64_t Off);
-  // Track Symbols that already have a Thunk
-  llvm::DenseMap<SymbolBody *, Thunk *> ThunkedSymbols;
+  // Record all the available Thunks for a Symbol
+  llvm::DenseMap<SymbolBody *, std::vector<Thunk *>> ThunkedSymbols;
 
   // Find a Thunk from the Thunks symbol definition, we can use this to find
   // the Thunk from a relocation to the Thunks symbol definition.
   llvm::DenseMap<SymbolBody *, Thunk *> Thunks;
 
-  // Track InputSections that have a ThunkSection placed in front
+  // Track InputSections that have an inline ThunkSection placed in front
+  // an inline ThunkSection may have control fall through to the section below
+  // so we need to make sure that there is only one of them.
+  // The Mips LA25 Thunk is an example of an inline ThunkSection.
   llvm::DenseMap<InputSection *, ThunkSection *> ThunkedSections;
 
   // All the ThunkSections that we have created, organised by OutputSection
   // will contain a mix of ThunkSections that have been created this pass, and
   // ThunkSections that have been merged into the OutputSection on previous
   // passes
   std::map<std::vector<InputSection *> *, std::vector<ThunkSection *>>
       ThunkSections;

lld/trunk/ELF/Relocations.cpp

ThunkSection *ThunkCreator::addThunkSection(OutputSection *OS,
   auto *TS = make<ThunkSection>(OS, Off);
   ThunkSections[ISR].push_back(TS);
   return TS;
 }
 
 
 std::pair<Thunk *, bool> ThunkCreator::getThunk(SymbolBody &Body,
                                                 uint32_t Type) {
-  auto res = ThunkedSymbols.insert({&Body, nullptr});
-  if (res.second || !res.first->second->isCompatibleWith(Type))
-    res.first->second = addThunk(Type, Body);
-  return std::make_pair(res.first->second, res.second);
+  auto Res = ThunkedSymbols.insert({&Body, std::vector<Thunk *>()});
+  if (!Res.second) {
+    // Check existing Thunks for Body to see if they can be reused
+    for (Thunk *ET : Res.first->second)
+      if (ET->isCompatibleWith(Type))
+        return {ET, false};
+  }
+  // No existing compatible Thunk in range, create a new one
+  Thunk *T = addThunk(Type, Body);
+  Res.first->second.push_back(T);
+  return {T, true};
 }
 
 // Call Fn on every executable InputSection accessed via the linker script
 // InputSectionDescription::Sections.
 void ThunkCreator::forEachExecInputSection(
     ArrayRef<OutputSectionCommand *> OutputSections,
     std::function<void(OutputSection *, std::vector<InputSection *> *,
                        InputSection *)>