ScopDetection: Only detect scops that have at least one read and one write

Scops that only read seem generally uninteresting and scops that only write are
most likely initializations where there is also little to optimize.  To not
waste compile time we bail early.

Differential Revision: http://reviews.llvm.org/D7735

llvm-svn: 229820

1 files changed, 14 insertions, 1 deletions

diff --git a/polly/lib/Analysis/ScopDetection.cpp b/polly/lib/Analysis/ScopDetection.cpp
index 4bb2b15cb41..8ef657a967a 100644
--- a/polly/lib/Analysis/ScopDetection.cpp
+++ b/polly/lib/Analysis/ScopDetection.cpp
@@ -84,6 +84,11 @@ static cl::opt<bool>
                               cl::Hidden, cl::init(false), cl::ZeroOrMore,
                               cl::cat(PollyCategory));
 
+static cl::opt<bool> DetectUnprofitable("polly-detect-unprofitable",
+                                        cl::desc("Detect unprofitable scops"),
+                                        cl::Hidden, cl::init(false),
+                                        cl::ZeroOrMore, cl::cat(PollyCategory));
+
 static cl::opt<std::string> OnlyFunction(
     "polly-only-func",
     cl::desc("Only run on functions that contain a certain string"),
@@ -623,8 +628,11 @@ bool ScopDetection::isValidInstruction(Instruction &Inst,
   }
 
   // Check the access function.
-  if (isa<LoadInst>(Inst) || isa<StoreInst>(Inst))
+  if (isa<LoadInst>(Inst) || isa<StoreInst>(Inst)) {
+    Context.hasStores |= isa<StoreInst>(Inst);
+    Context.hasLoads |= isa<LoadInst>(Inst);
     return isValidMemoryAccess(Inst, Context);
+  }
 
   // We do not know this instruction, therefore we assume it is invalid.
   return invalid<ReportUnknownInst>(Context, /*Assert=*/true, &Inst);
@@ -868,6 +876,11 @@ bool ScopDetection::isValidRegion(DetectionContext &Context) const {
   if (!allBlocksValid(Context))
     return false;
 
+  // We can probably not do a lot on scops that only write or only read
+  // data.
+  if (!DetectUnprofitable && (!Context.hasStores || !Context.hasLoads))
+    invalid<ReportUnprofitable>(Context, /*Assert=*/true);
+
   DEBUG(dbgs() << "OK\n");
   return true;
 }