Teach the cost model about the optimization in r169904: Truncation of induction variables costs the same as scalar trunc.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@170051 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 21 insertions, 3 deletions

diff --git a/lib/Transforms/Vectorize/LoopVectorize.cpp b/lib/Transforms/Vectorize/LoopVectorize.cpp
index cdd130f135..475bea1485 100644
--- a/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -106,8 +106,7 @@ struct LoopVectorize : public LoopPass {
     }
 
     DEBUG(dbgs() << "LV: Found a vectorizable loop ("<< VF << ") in "<<
-          L->getHeader()->getParent()->getParent()->getModuleIdentifier()<<
-          "\n");
+          F->getParent()->getModuleIdentifier()<<"\n");
 
     // If we decided that it is *legal* to vectorizer the loop then do it.
     InnerLoopVectorizer LB(L, SE, LI, DT, DL, VF);
@@ -1849,6 +1848,15 @@ LoopVectorizationLegality::isInductionVariable(PHINode *Phi) {
   return NoInduction;
 }
 
+bool LoopVectorizationLegality::isInductionVariable(const Value *V) {
+  Value *In0 = const_cast<Value*>(V);
+  PHINode *PN = dyn_cast_or_null<PHINode>(In0);
+  if (!PN)
+    return false;
+
+  return Inductions.count(PN);
+}
+
 bool LoopVectorizationLegality::blockNeedsPredication(BasicBlock *BB)  {
   assert(TheLoop->contains(BB) && "Unknown block used");
 
@@ -2110,6 +2118,13 @@ LoopVectorizationCostModel::getInstructionCost(Instruction *I, unsigned VF) {
   case Instruction::Trunc:
   case Instruction::FPTrunc:
   case Instruction::BitCast: {
+    // We optimize the truncation of induction variable.
+    // The cost of these is the same as the scalar operation.
+    if (I->getOpcode() == Instruction::Trunc &&
+        Legal->isInductionVariable(I->getOperand(0)))
+         return VTTI->getCastInstrCost(I->getOpcode(), I->getType(),
+                                       I->getOperand(0)->getType());
+
     Type *SrcVecTy = ToVectorTy(I->getOperand(0)->getType(), VF);
     return VTTI->getCastInstrCost(I->getOpcode(), VectorTy, SrcVecTy);
   }
diff --git a/lib/Transforms/Vectorize/LoopVectorize.h b/lib/Transforms/Vectorize/LoopVectorize.h
index e5a5259605..e5ef29052e 100644
--- a/lib/Transforms/Vectorize/LoopVectorize.h
+++ b/lib/Transforms/Vectorize/LoopVectorize.h
@@ -320,6 +320,9 @@ public:
   /// Returns the induction variables found in the loop.
   InductionList *getInductionVars() { return &Inductions; }
 
+  /// Returns True if V is an induction variable in this loop.
+  bool isInductionVariable(const Value *V);
+
   /// Return true if the block BB needs to be predicated in order for the loop
   /// to be vectorized.
   bool blockNeedsPredication(BasicBlock *BB);
diff --git a/test/Transforms/LoopVectorize/X86/conversion-cost.ll b/test/Transforms/LoopVectorize/X86/conversion-cost.ll
index 8f1bb545fa..60c742e220 100644
--- a/test/Transforms/LoopVectorize/X86/conversion-cost.ll
+++ b/test/Transforms/LoopVectorize/X86/conversion-cost.ll
@@ -4,7 +4,7 @@ target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f3
 target triple = "x86_64-apple-macosx10.8.0"
 
 ;CHECK: @conversion_cost1
-;CHECK: store <2 x i8>
+;CHECK: store <8 x i8>
 ;CHECK: ret
 define i32 @conversion_cost1(i32 %n, i8* nocapture %A, float* nocapture %B) nounwind uwtable ssp {
   %1 = icmp sgt i32 %n, 3