draftloop_unroll

need to disable unrolling for those loops have too large travel count.
and all its parent loop.

Signed-off-by: Zhigang Gong <zhigang.gong@intel.com>

1 files changed, 16 insertions, 1 deletions

diff --git a/backend/src/llvm/llvm_unroll.cpp b/backend/src/llvm/llvm_unroll.cpp
index de0bd5e7..6f10fd83 100644
--- a/backend/src/llvm/llvm_unroll.cpp
+++ b/backend/src/llvm/llvm_unroll.cpp
@@ -41,6 +41,7 @@
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/PassManager.h"
 #include "llvm/Transforms/Scalar.h"
+#include "llvm/Analysis/ScalarEvolution.h"
 #include "llvm/Analysis/LoopPass.h"
 #include "llvm/llvm_gen_backend.hpp"
 #include "sys/map.hpp"
@@ -63,6 +64,8 @@ namespace gbe {
         AU.addPreservedID(LoopSimplifyID);
         AU.addRequiredID(LCSSAID);
         AU.addPreservedID(LCSSAID);
+        AU.addRequired<ScalarEvolution>();
+        AU.addPreserved<ScalarEvolution>();
       }
 
       // Returns the value associated with the given metadata node name (for
@@ -95,7 +98,7 @@ namespace gbe {
 
       static void setForceUnrollID(Loop *L) {
         LLVMContext &Context = L->getHeader()->getContext();
-        SmallVector<Value *, 2> forceUnroll, unrollCount;
+        SmallVector<Value *, 2> forceUnroll;
         forceUnroll.push_back(MDString::get(Context, "llvm.loop.unroll.enable"));
         forceUnroll.push_back(ConstantInt::get(Type::getInt1Ty(Context), 1));
         MDNode *forceUnrollNode = MDNode::get(Context, forceUnroll);
@@ -118,6 +121,18 @@ namespace gbe {
         const ConstantInt *Count = GetUnrollMetadataValue(L, "llvm.loop.unroll.count");
         if (Count)
           return false;
+        ScalarEvolution *SE = &getAnalysis<ScalarEvolution>();
+        BasicBlock *LatchBlock = L->getLoopLatch();
+        unsigned TripCount = SE->getSmallConstantTripCount(L, LatchBlock);
+        if (TripCount > 32) {
+          // 32 is too large to unroll, let's disable the unrolling on it and all its parent loop.
+          Loop *parentL = L->getParentLoop();
+          while(parentL) {
+            setDisableUnrollID(parentL);
+            parentL = parentL->getParentLoop();
+          }
+        }
+
         const std::vector<Loop*> subLoops = L->getSubLoops();
         std::set<BasicBlock*> subBlocks, blocks;
         for(auto l : subLoops)