[LCG] Add aliased functions as LCG roots

[Carrot]

Summary

Current LCG doesn't check aliased functions. So if an internal function has a public alias it will not be added to CG SCC, but it is still reachable from outside through the alias.
So this patch adds aliased functions to SCC.

[tejohnson]

lib/Analysis/LazyCallGraph.cpp

192

Presumably aliases with internal linkage themselves can be ignored.

[chandlerc]

Good catch!

lib/Analysis/LazyCallGraph.cpp

191

I would rewrite the comment to more closely match the patch description: "Externally visible aliases of internal functions are also viable entry edges to the module."

192–200

All of this should go above I think, right after we walk the module. We want to have the complete entry edge set before we visit globals and do the reference visit walk.

196–197

Include the fact that it is being added due to an alias, and the name of that alias?

test/Analysis/LazyCallGraph/alias.ll

3

Also test that internal aliases *don't* become reachable?

[Carrot]

ping

[chandlerc]

LGTM!

test/Analysis/LazyCallGraph/alias.ll

24

nit: can drop this comment.

31

nit: same

39

nit: same

[Carrot]

Will check in this version.

lib/Analysis/LazyCallGraph.cpp

LazyCallGraph::LazyCallGraph(Module &M, TargetLibraryInfo &TLI) {
 
   LLVM_DEBUG(
       dbgs() << "  Adding functions referenced by global initializers to the "
                 "entry set.\n");
   visitReferences(Worklist, Visited, [&](Function &F) {
     addEdge(EntryEdges.Edges, EntryEdges.EdgeIndexMap, get(F),
             LazyCallGraph::Edge::Ref);
   });
+
+  // Functions has alias are also reachable.
+  for (auto &A : M.aliases()) {
+    if (A.hasLocalLinkage())
+      continue;
+    if (Function* F = dyn_cast<Function>(A.getAliasee())) {
+      LLVM_DEBUG(dbgs() << "  Adding '" << F->getName()
+                        << "' to entry set of the graph.\n");
+      addEdge(EntryEdges.Edges, EntryEdges.EdgeIndexMap, get(*F), Edge::Ref);
+    }
+  }
 }
 
 LazyCallGraph::LazyCallGraph(LazyCallGraph &&G)
     : BPA(std::move(G.BPA)), NodeMap(std::move(G.NodeMap)),
       EntryEdges(std::move(G.EntryEdges)), SCCBPA(std::move(G.SCCBPA)),
       SCCMap(std::move(G.SCCMap)),
       LibFunctions(std::move(G.LibFunctions)) {
   updateGraphPtrs();

test/Analysis/LazyCallGraph/alias.ll

+; RUN: opt -disable-output -passes=print-lcg %s 2>&1 | FileCheck %s
+;
+; Aliased function should be reachable in CGSCC.
+
+target triple = "x86_64-grtev4-linux-gnu"
+
+; CHECK:        RefSCC with 1 call SCCs:
+; CHECK-NEXT:     SCC with 1 functions:
+; CHECK-NEXT:       bar
+
+; CHECK:       RefSCC with 1 call SCCs:
+; CHECK-NEXT:    SCC with 1 functions:
+; CHECK-NEXT:      foo
+
+
+@alias1 = weak dso_local alias i8* (i8*), i8* (i8*)* @foo
+
+; Function Attrs: nounwind uwtable
+define dso_local i8* @foo(i8* %returned) {
+  ret i8* %returned
+}
+
+@alias2 = weak dso_local alias i8* (i8*), i8* (i8*)* @bar
+
+; Function Attrs: nounwind uwtable
+define internal i8* @bar(i8* %returned) {
+  ret i8* %returned
+}
+