Weaken profitability constraints during ScopDetection

  Regions with one affine loop can be profitable if the loop is
  distributable. To this end we will allow them to be treated as
  profitable if they contain at least two non-trivial basic blocks.

llvm-svn: 269064

1 files changed, 24 insertions, 0 deletions

diff --git a/polly/lib/Analysis/ScopDetection.cpp b/polly/lib/Analysis/ScopDetection.cpp
index 4ee92fcfa93..34f439bae0b 100644
--- a/polly/lib/Analysis/ScopDetection.cpp
+++ b/polly/lib/Analysis/ScopDetection.cpp
@@ -1269,6 +1269,26 @@ bool ScopDetection::hasSufficientCompute(DetectionContext &Context,
   return InstCount >= ProfitabilityMinPerLoopInstructions;
 }
 
+bool ScopDetection::hasPossiblyDistributableLoop(
+    DetectionContext &Context) const {
+  for (auto *BB : Context.CurRegion.blocks()) {
+    auto *L = LI->getLoopFor(BB);
+    if (!Context.CurRegion.contains(L))
+      continue;
+    if (Context.BoxedLoopsSet.count(L))
+      continue;
+    unsigned StmtsWithStoresInLoops = 0;
+    for (auto *LBB : L->blocks()) {
+      bool MemStore = false;
+      for (auto &I : *LBB)
+        MemStore |= isa<StoreInst>(&I);
+      StmtsWithStoresInLoops += MemStore;
+    }
+    return (StmtsWithStoresInLoops > 1);
+  }
+  return false;
+}
+
 bool ScopDetection::isProfitableRegion(DetectionContext &Context) const {
   Region &CurRegion = Context.CurRegion;
 
@@ -1288,6 +1308,10 @@ bool ScopDetection::isProfitableRegion(DetectionContext &Context) const {
   if (NumAffineLoops >= 2)
     return true;
 
+  // A loop with multiple non-trivial blocks migt be amendable to distribution.
+  if (NumAffineLoops == 1 && hasPossiblyDistributableLoop(Context))
+    return true;
+
   // Scops that contain a loop with a non-trivial amount of computation per
   // loop-iteration are interesting as we may be able to parallelize such
   // loops. Individual loops that have only a small amount of computation