Inliner: Non-local functions in COMDATs shouldn't be dropped

A function with discardable linkage cannot be discarded if its a member
of a COMDAT group without considering all the other COMDAT members as
well.  This sort of thing is already handled by GlobalOpt/GlobalDCE.

This fixes PR21206.

llvm-svn: 219335

llvm/lib/Transforms/IPO/Inliner.cpp

@@ -669,6 +669,13 @@ bool Inliner::removeDeadFunctions(CallGraph &CG, bool AlwaysInlineOnly) {
 
     if (!F->isDefTriviallyDead())
       continue;
+
+    // It is unsafe to drop a function with discardable linkage from a COMDAT
+    // without also dropping the other members of the COMDAT.
+    // The inliner doesn't visit non-function entities which are in COMDAT
+    // groups so it is unsafe to do so *unless* the linkage is local.
+    if (!F->hasLocalLinkage() && F->hasComdat())
+      continue;
     
     // Remove any call graph edges from the function to its callees.
     CGN->removeAllCalledFunctions();

llvm/test/Transforms/Inline/pr21206.ll

@@ -0,0 +1,18 @@
+; RUN: opt < %s -inline -S | FileCheck %s
+
+$c = comdat any
+; CHECK: $c = comdat any
+
+define linkonce_odr void @foo() comdat $c {
+  ret void
+}
+; CHECK: define linkonce_odr void @foo() comdat $c
+
+define linkonce_odr void @bar() comdat $c {
+  ret void
+}
+; CHECK: define linkonce_odr void @bar() comdat $c
+
+define void()* @zed()  {
+  ret void()* @foo
+}