[llvm] [ORC] Add absoluteSymbolsLinkGraph to expose absolute symbols to platform (PR #77008)

[via llvm-commits]

================
@@ -48,15 +48,22 @@ void JITLinkerBase::linkPhase1(std::unique_ptr<JITLinkerBase> Self) {
   if (auto Err = runPasses(Passes.PostPrunePasses))
     return Ctx->notifyFailed(std::move(Err));
 
-  Ctx->getMemoryManager().allocate(
-      Ctx->getJITLinkDylib(), *G,
-      [S = std::move(Self)](AllocResult AR) mutable {
-        // FIXME: Once MSVC implements c++17 order of evaluation rules for calls
-        // this can be simplified to
-        //          S->linkPhase2(std::move(S), std::move(AR));
-        auto *TmpSelf = S.get();
-        TmpSelf->linkPhase2(std::move(S), std::move(AR));
-      });
+  auto LinkPhase2 = [S = std::move(Self)](AllocResult AR) mutable {
+    // FIXME: Once MSVC implements c++17 order of evaluation rules for calls
+    // this can be simplified to
+    //          S->linkPhase2(std::move(S), std::move(AR));
+    auto *TmpSelf = S.get();
+    TmpSelf->linkPhase2(std::move(S), std::move(AR));
+  };
+
+  if (G->allocActions().empty() && llvm::all_of(G->sections(), [](Section &S) {
+        return S.getMemLifetime() == orc::MemLifetime::NoAlloc;
+      })) {
+    LinkPhase2(nullptr);
+  } else {
+    Ctx->getMemoryManager().allocate(Ctx->getJITLinkDylib(), *G,
+                                     std::move(LinkPhase2));
+  }
----------------
lhames wrote:

Alternatively this could also be:
```c++
  // Skip straight to phase 2 if the graph is empty and has no associated actions.
  if (G->allocActions().empty() && llvm::all_of(G->sections(), [](Section &S) {
        return S.getMemLifetime() == orc::MemLifetime::NoAlloc;
      })) {
    linkPhase2(std::move(Self), nullptr);
    return;
  }
  
  Ctx->getMemoryManager().allocate(Ctx->getJITLinkDylib(), *G,
                                   [S = std::move(Self)](AllocResult AR) mutable {
      // FIXME: Once MSVC implements c++17 order of evaluation rules for calls
      // this can be simplified to
      //          S->linkPhase2(std::move(S), std::move(AR));
      auto *TmpSelf = S.get();
      TmpSelf->linkPhase2(std::move(S), std::move(AR));
    });
  ```
Similarly for the call to phase 4.
 
That reads more clearly to me, but only marginally.

https://github.com/llvm/llvm-project/pull/77008