Re-apply "[ORC][JITLink] Add jitlink::Scope::SideEffectsOnly" with fixes.

This reapplies aba6bb0, which was reverted in 28e2a89 due to bot
failures. It contains fixes to silence warnings for uncovered switches,
and for incorrect initializer-symbol handling on ELF and COFF.

Author: lhames

llvm/include/llvm/ExecutionEngine/JITLink/JITLink.h

@@ -393,10 +393,13 @@ const char *getLinkageName(Linkage L);
 /// Defines the scope in which this symbol should be visible:
 ///   Default -- Visible in the public interface of the linkage unit.
 ///   Hidden -- Visible within the linkage unit, but not exported from it.
+///   SideEffectsOnly -- Like hidden, but symbol can only be looked up once
+///                      to trigger materialization of the containing graph.
 ///   Local -- Visible only within the LinkGraph.
 enum class Scope : uint8_t {
   Default,
   Hidden,
+  SideEffectsOnly,
   Local
 };
 

llvm/lib/ExecutionEngine/JITLink/JITLink.cpp

@@ -85,6 +85,8 @@ const char *getScopeName(Scope S) {
     return "default";
   case Scope::Hidden:
     return "hidden";
+  case Scope::SideEffectsOnly:
+    return "side-effects-only";
   case Scope::Local:
     return "local";
   }

llvm/lib/ExecutionEngine/JITLink/JITLinkGeneric.cpp

@@ -253,7 +253,9 @@ void JITLinkerBase::applyLookupResult(AsyncLookupResult Result) {
       }
       switch (Sym->getScope()) {
       case Scope::Local:
-        llvm_unreachable("External symbol should not have local linkage");
+      case Scope::SideEffectsOnly:
+        llvm_unreachable("External symbol should not have local or "
+                         "side-effects-only linkage");
       case Scope::Hidden:
         break;
       case Scope::Default:

llvm/lib/ExecutionEngine/Orc/COFFPlatform.cpp

@@ -862,9 +862,9 @@ Error COFFPlatform::COFFPlatformPlugin::preserveInitializerSections(
       // to the first block.
       if (!InitSym) {
         auto &B = **InitSection.blocks().begin();
-        InitSym = &G.addDefinedSymbol(B, 0, *InitSymName, B.getSize(),
-                                      jitlink::Linkage::Strong,
-                                      jitlink::Scope::Default, false, true);
+        InitSym = &G.addDefinedSymbol(
+            B, 0, *InitSymName, B.getSize(), jitlink::Linkage::Strong,
+            jitlink::Scope::SideEffectsOnly, false, true);
       }
 
       // Add keep-alive edges to anonymous symbols in all other init blocks.

llvm/lib/ExecutionEngine/Orc/ELFNixPlatform.cpp

@@ -894,9 +894,9 @@ Error ELFNixPlatform::ELFNixPlatformPlugin::preserveInitSections(
       // to the first block.
       if (!InitSym) {
         auto &B = **InitSection.blocks().begin();
-        InitSym = &G.addDefinedSymbol(B, 0, *InitSymName, B.getSize(),
-                                      jitlink::Linkage::Strong,
-                                      jitlink::Scope::Default, false, true);
+        InitSym = &G.addDefinedSymbol(
+            B, 0, *InitSymName, B.getSize(), jitlink::Linkage::Strong,
+            jitlink::Scope::SideEffectsOnly, false, true);
       }
 
       // Add keep-alive edges to anonymous symbols in all other init blocks.

llvm/lib/ExecutionEngine/Orc/MachOPlatform.cpp

@@ -1001,9 +1001,9 @@ Error MachOPlatform::MachOPlatformPlugin::preserveImportantSections(
       // to the first block.
       if (!InitSym) {
         auto &B = **InitSection->blocks().begin();
-        InitSym = &G.addDefinedSymbol(B, 0, *InitSymName, B.getSize(),
-                                      jitlink::Linkage::Strong,
-                                      jitlink::Scope::Default, false, true);
+        InitSym = &G.addDefinedSymbol(
+            B, 0, *InitSymName, B.getSize(), jitlink::Linkage::Strong,
+            jitlink::Scope::SideEffectsOnly, false, true);
       }
 
       // Add keep-alive edges to anonymous symbols in all other init blocks.

llvm/lib/ExecutionEngine/Orc/ObjectLinkingLayer.cpp

@@ -65,6 +65,8 @@ JITSymbolFlags getJITSymbolFlagsForSymbol(Symbol &Sym) {
 
   if (Sym.getScope() == Scope::Default)
     Flags |= JITSymbolFlags::Exported;
+  else if (Sym.getScope() == Scope::SideEffectsOnly)
+    Flags |= JITSymbolFlags::MaterializationSideEffectsOnly;
 
   if (Sym.isCallable())
     Flags |= JITSymbolFlags::Callable;
@@ -236,7 +238,7 @@ class ObjectLinkingLayerJITLinkContext final : public JITLinkContext {
 
     SymbolMap InternedResult;
     for (auto *Sym : G.defined_symbols())
-      if (Sym->getScope() != Scope::Local) {
+      if (Sym->getScope() < Scope::SideEffectsOnly) {
         auto InternedName = ES.intern(Sym->getName());
         auto Ptr = getJITSymbolPtrForSymbol(*Sym, G.getTargetTriple());
         auto Flags = getJITSymbolFlagsForSymbol(*Sym);
@@ -249,7 +251,7 @@ class ObjectLinkingLayerJITLinkContext final : public JITLinkContext {
       }
 
     for (auto *Sym : G.absolute_symbols())
-      if (Sym->getScope() != Scope::Local) {
+      if (Sym->getScope() < Scope::SideEffectsOnly) {
         auto InternedName = ES.intern(Sym->getName());
         auto Ptr = getJITSymbolPtrForSymbol(*Sym, G.getTargetTriple());
         auto Flags = getJITSymbolFlagsForSymbol(*Sym);
@@ -281,11 +283,9 @@ class ObjectLinkingLayerJITLinkContext final : public JITLinkContext {
         // If this is a materialization-side-effects only symbol then bump
         // the counter and remove in from the result, otherwise make sure that
         // it's defined.
-        if (Flags.hasMaterializationSideEffectsOnly()) {
+        if (Flags.hasMaterializationSideEffectsOnly())
           ++NumMaterializationSideEffectsOnlySymbols;
-          InternedResult.erase(Sym);
-          continue;
-        } else if (I == InternedResult.end())
+        else if (I == InternedResult.end())
           MissingSymbols.push_back(Sym);
         else if (Layer.OverrideObjectFlags)
           I->second.setFlags(Flags);