fix PR5009 by making CGSCCPM realize that a call was devirtualized

if an indirect call site was removed and a direct one was added, not
just if an indirect call site was modified to be direct.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@102830 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 36 insertions, 5 deletions

diff --git a/lib/Analysis/IPA/CallGraphSCCPass.cpp b/lib/Analysis/IPA/CallGraphSCCPass.cpp
index 288a7ef158..0c01ee5b82 100644
--- a/lib/Analysis/IPA/CallGraphSCCPass.cpp
+++ b/lib/Analysis/IPA/CallGraphSCCPass.cpp
@@ -191,6 +191,10 @@ bool CGPassManager::RefreshCallGraph(CallGraphSCC &CurSCC,
     
     // Walk the function body looking for call sites.  Sync up the call sites in
     // CGN with those actually in the function.
+
+    // Keep track of the number of direct and indirect calls that were
+    // invalidated and removed.
+    unsigned NumDirectRemoved = 0, NumIndirectRemoved = 0;
     
     // Get the set of call sites currently in the function.
     for (CallGraphNode::iterator I = CGN->begin(), E = CGN->end(); I != E; ) {
@@ -209,6 +213,12 @@ bool CGPassManager::RefreshCallGraph(CallGraphSCC &CurSCC,
         assert(!CheckingMode &&
                "CallGraphSCCPass did not update the CallGraph correctly!");
         
+        // If this was an indirect call site, count it.
+        if (I->second->getFunction() == 0)
+          ++NumIndirectRemoved;
+        else 
+          ++NumDirectRemoved;
+        
         // Just remove the edge from the set of callees, keep track of whether
         // I points to the last element of the vector.
         bool WasLast = I + 1 == E;
@@ -230,6 +240,9 @@ bool CGPassManager::RefreshCallGraph(CallGraphSCC &CurSCC,
     }
     
     // Loop over all of the instructions in the function, getting the callsites.
+    // Keep track of the number of direct/indirect calls added.
+    unsigned NumDirectAdded = 0, NumIndirectAdded = 0;
+    
     for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
       for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
         CallSite CS = CallSite::get(I);
@@ -286,19 +299,34 @@ bool CGPassManager::RefreshCallGraph(CallGraphSCC &CurSCC,
         assert(!CheckingMode &&
                "CallGraphSCCPass did not update the CallGraph correctly!");
 
-        // If the call site didn't exist in the CGN yet, add it.  We assume that
-        // newly introduced call sites won't be indirect.  This could be fixed
-        // in the future.
+        // If the call site didn't exist in the CGN yet, add it.
         CallGraphNode *CalleeNode;
-        if (Function *Callee = CS.getCalledFunction())
+        if (Function *Callee = CS.getCalledFunction()) {
           CalleeNode = CG.getOrInsertFunction(Callee);
-        else
+          ++NumDirectAdded;
+        } else {
           CalleeNode = CG.getCallsExternalNode();
+          ++NumIndirectAdded;
+        }
         
         CGN->addCalledFunction(CS, CalleeNode);
         MadeChange = true;
       }
     
+    // We scanned the old callgraph node, removing invalidated call sites and
+    // then added back newly found call sites.  One thing that can happen is
+    // that an old indirect call site was deleted and replaced with a new direct
+    // call.  In this case, we have devirtualized a call, and CGSCCPM would like
+    // to iteratively optimize the new code.  Unfortunately, we don't really
+    // have a great way to detect when this happens.  As an approximation, we
+    // just look at whether the number of indirect calls is reduced and the
+    // number of direct calls is increased.  There are tons of ways to fool this
+    // (e.g. DCE'ing an indirect call and duplicating an unrelated block with a
+    // direct call) but this is close enough.
+    if (NumIndirectRemoved > NumIndirectAdded &&
+        NumDirectRemoved < NumDirectAdded)
+      DevirtualizedCall = true;
+    
     // After scanning this function, if we still have entries in callsites, then
     // they are dangling pointers.  WeakVH should save us for this, so abort if
     // this happens.
@@ -315,6 +343,9 @@ bool CGPassManager::RefreshCallGraph(CallGraphSCC &CurSCC,
           for (CallGraphSCC::iterator I = CurSCC.begin(), E = CurSCC.end();
             I != E; ++I)
               (*I)->dump();
+          if (DevirtualizedCall)
+            dbgs() << "CGSCCPASSMGR: Refresh devirtualized a call!\n";
+
          } else {
            dbgs() << "CGSCCPASSMGR: SCC Refresh didn't change call graph.\n";
          }