[SI] Create Scop Name lazily

Summary: Creating the Scop name is expensive, because creating the
Region name it's derived from is expensive. So create the name lazily,
because getName() is actually called rarely.

This is a reiteration of r328666, which introduced a use-after-free and
got reverted in r331363.

Differential Revision: https://reviews.llvm.org/D46868

llvm-svn: 332359

polly/include/polly/ScopInfo.h

@@ -25,6 +25,7 @@
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/MapVector.h"
+#include "llvm/ADT/Optional.h"
 #include "llvm/ADT/SetVector.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringMap.h"
@@ -1717,7 +1718,7 @@ private:
   Region &R;
 
   /// The name of the SCoP (identical to the regions name)
-  std::string name;
+  Optional<std::string> name;
 
   /// The ID to be assigned to the next Scop in a function
   static int NextScopID;
@@ -2455,7 +2456,11 @@ public:
   /// could be executed.
   bool isEmpty() const { return Stmts.empty(); }
 
-  const StringRef getName() const { return name; }
+  StringRef getName() {
+    if (!name)
+      name = R.getNameStr();
+    return *name;
+  }
 
   using array_iterator = ArrayInfoSetTy::iterator;
   using const_array_iterator = ArrayInfoSetTy::const_iterator;

polly/lib/Analysis/ScopInfo.cpp

@@ -3328,8 +3328,8 @@ Scop::Scop(Region &R, ScalarEvolution &ScalarEvolution, LoopInfo &LI,
            DominatorTree &DT, ScopDetection::DetectionContext &DC,
            OptimizationRemarkEmitter &ORE)
     : IslCtx(isl_ctx_alloc(), isl_ctx_free), SE(&ScalarEvolution), DT(&DT),
-      R(R), name(R.getNameStr()), HasSingleExitEdge(R.getExitingBlock()),
-      DC(DC), ORE(ORE), Affinator(this, LI),
+      R(R), name(None), HasSingleExitEdge(R.getExitingBlock()), DC(DC),
+      ORE(ORE), Affinator(this, LI),
       ID(getNextID((*R.getEntry()->getParent()).getName().str())) {
   if (IslOnErrorAbort)
     isl_options_set_on_error(getIslCtx().get(), ISL_ON_ERROR_ABORT);