[Devirtualization] statistic for number of devirtualized calls

[davide]

Testcase? (-stats + REQUIRE: asserts)

[Prazek]

It turned out that this is invalid way of collecting this statistic, because we don't count devirtualization that happens without previous inlining like:

define void @devirtualize(i8* %p) {
%x = bitcast i8* %p to void()**
store void()* @foo, void()** %x
%c = load void()*, void()** %x
call void %c()
call void @foo()
call void %c()
ret void
}

The stat probably will need to be collected in GVN instead.

lib/Analysis/CallGraphSCCPass.cpp

 using namespace llvm;
 
 #define DEBUG_TYPE "cgscc-passmgr"
 
 static cl::opt<unsigned> 
 MaxIterations("max-cg-scc-iterations", cl::ReallyHidden, cl::init(4));
 
 STATISTIC(MaxSCCIterations, "Maximum CGSCCPassMgr iterations on one SCC");
-
+STATISTIC(NumDevirtualized, "Number of devirtualized calls");
 //===----------------------------------------------------------------------===//
 // CGPassManager
 //
 /// CGPassManager manages FPPassManagers and CallGraphSCCPasses.
 
 namespace {
 
 class CGPassManager : public ModulePass, public PMDataManager {
for (BasicBlock &BB : *F)
           // If not, we either went from a direct call to indirect, indirect to
           // direct, or direct to different direct.
           CallGraphNode *CalleeNode;
           if (Function *Callee = CS.getCalledFunction()) {
             CalleeNode = CG.getOrInsertFunction(Callee);
             // Keep track of whether we turned an indirect call into a direct
             // one.
             if (!ExistingNode->getFunction()) {
+              NumDevirtualized++;
               DevirtualizedCall = true;
               DEBUG(dbgs() << "  CGSCCPASSMGR: Devirtualized call to '"
                            << Callee->getName() << "'\n");
             }
           } else {
             CalleeNode = CG.getCallsExternalNode();
           }