Refactor code from inlining and globalopt that checks whether a function definition is unused, and enhance it so it can tell that functions which are only used by a blockaddress are in fact dead. This probably doesn't happen much on most code, but the Linux kernel's _THIS_IP_ can trigger this issue with blockaddress. (GlobalDCE can also handle the given tescase, but we only run that at -O3.) Found while looking at PR11180.

llvm-svn: 142572

1 files changed, 15 insertions, 0 deletions

diff --git a/llvm/lib/VMCore/Function.cpp b/llvm/lib/VMCore/Function.cpp
index be0f0567044..bb8f62ac295 100644
--- a/llvm/lib/VMCore/Function.cpp
+++ b/llvm/lib/VMCore/Function.cpp
@@ -402,6 +402,7 @@ Function *Intrinsic::getDeclaration(Module *M, ID id, ArrayRef<Type*> Tys) {
 bool Function::hasAddressTaken(const User* *PutOffender) const {
   for (Value::const_use_iterator I = use_begin(), E = use_end(); I != E; ++I) {
     const User *U = *I;
+    // FIXME: Check for blockaddress, which does not take the address.
     if (!isa<CallInst>(U) && !isa<InvokeInst>(U))
       return PutOffender ? (*PutOffender = U, true) : true;
     ImmutableCallSite CS(cast<Instruction>(U));
@@ -411,6 +412,20 @@ bool Function::hasAddressTaken(const User* *PutOffender) const {
   return false;
 }
 
+bool Function::isDefTriviallyDead() const {
+  // Check the linkage
+  if (!hasLinkOnceLinkage() && !hasLocalLinkage() &&
+      !hasAvailableExternallyLinkage())
+    return false;
+
+  // Check if the function is used by anything other than a blockaddress.
+  for (Value::const_use_iterator I = use_begin(), E = use_end(); I != E; ++I)
+    if (!isa<BlockAddress>(*I))
+      return false;
+
+  return true;
+}
+
 /// callsFunctionThatReturnsTwice - Return true if the function has a call to
 /// setjmp or other function that gcc recognizes as "returning twice".
 bool Function::callsFunctionThatReturnsTwice() const {