From 36fc9c31072f5daf8e99de554f6531f4b989772b Mon Sep 17 00:00:00 2001
From: Guozhi Wei <carrot@google.com>
Date: Fri, 5 Apr 2019 18:51:08 +0000
Subject: [PATCH] [LCG] Add aliased functions as LCG roots

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.

Differential Revision: https://reviews.llvm.org/D59898

llvm-svn: 357795
---
 llvm/lib/Analysis/LazyCallGraph.cpp       | 13 ++++++++
 llvm/test/Analysis/LazyCallGraph/alias.ll | 38 +++++++++++++++++++++++
 2 files changed, 51 insertions(+)
 create mode 100644 llvm/test/Analysis/LazyCallGraph/alias.ll

diff --git a/llvm/lib/Analysis/LazyCallGraph.cpp b/llvm/lib/Analysis/LazyCallGraph.cpp
index 726f52a95855..797fcf516429 100644
--- a/llvm/lib/Analysis/LazyCallGraph.cpp
+++ b/llvm/lib/Analysis/LazyCallGraph.cpp
@@ -172,6 +172,19 @@ LazyCallGraph::LazyCallGraph(Module &M, TargetLibraryInfo &TLI) {
     addEdge(EntryEdges.Edges, EntryEdges.EdgeIndexMap, get(F), Edge::Ref);
   }
 
+  // Externally visible aliases of internal functions are also viable entry
+  // edges to the module.
+  for (auto &A : M.aliases()) {
+    if (A.hasLocalLinkage())
+      continue;
+    if (Function* F = dyn_cast<Function>(A.getAliasee())) {
+      LLVM_DEBUG(dbgs() << "  Adding '" << F->getName()
+                        << "' with alias '" << A.getName()
+                        << "' to entry set of the graph.\n");
+      addEdge(EntryEdges.Edges, EntryEdges.EdgeIndexMap, get(*F), Edge::Ref);
+    }
+  }
+
   // Now add entry nodes for functions reachable via initializers to globals.
   SmallVector<Constant *, 16> Worklist;
   SmallPtrSet<Constant *, 16> Visited;
diff --git a/llvm/test/Analysis/LazyCallGraph/alias.ll b/llvm/test/Analysis/LazyCallGraph/alias.ll
new file mode 100644
index 000000000000..7c9ca5182f91
--- /dev/null
+++ b/llvm/test/Analysis/LazyCallGraph/alias.ll
@@ -0,0 +1,38 @@
+; 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:        Edges in function: foo
+; CHECK:        Edges in function: bar
+; CHECK:        Edges in function: baz
+
+; 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
+
+; CHECK-NOT:       baz
+
+@alias1 = weak dso_local alias i8* (i8*), i8* (i8*)* @foo
+
+define dso_local i8* @foo(i8* %returned) {
+  ret i8* %returned
+}
+
+@alias2 = weak dso_local alias i8* (i8*), i8* (i8*)* @bar
+
+define internal i8* @bar(i8* %returned) {
+  ret i8* %returned
+}
+
+; Internal alias is not reachable.
+@alias3 = internal alias i8* (i8*), i8* (i8*)* @baz
+
+define internal i8* @baz(i8* %returned) {
+  ret i8* %returned
+}