[LoopVectorizer, TTI] New method supportsEfficientVectorElementLoadStore()

Since SystemZ supports vector element load/store instructions, there is no
need for extracts/inserts if a vector load/store gets scalarized.

This patch lets Target specify that it supports such instructions by means of
a new TTI hook that defaults to false.

The use for this is in the LoopVectorizer getScalarizationOverhead() method,
which will with this patch produce a smaller sum for a vector load/store on
SystemZ.

New test: test/Transforms/LoopVectorize/SystemZ/load-store-scalarization-cost.ll

Review: Adam Nemet
https://reviews.llvm.org/D30680

llvm-svn: 300056

3 files changed, 11 insertions, 2 deletions

diff --git a/llvm/lib/Analysis/TargetTransformInfo.cpp b/llvm/lib/Analysis/TargetTransformInfo.cpp
index c8b8740bd85..d73b1a12803 100644
--- a/llvm/lib/Analysis/TargetTransformInfo.cpp
+++ b/llvm/lib/Analysis/TargetTransformInfo.cpp
@@ -197,6 +197,10 @@ getOperandsScalarizationOverhead(ArrayRef<const Value *> Args,
   return TTIImpl->getOperandsScalarizationOverhead(Args, VF);
 }
 
+bool TargetTransformInfo::supportsEfficientVectorElementLoadStore() const {
+  return TTIImpl->supportsEfficientVectorElementLoadStore();
+}
+
 bool TargetTransformInfo::enableAggressiveInterleaving(bool LoopHasReductions) const {
   return TTIImpl->enableAggressiveInterleaving(LoopHasReductions);
 }
diff --git a/llvm/lib/Target/SystemZ/SystemZTargetTransformInfo.h b/llvm/lib/Target/SystemZ/SystemZTargetTransformInfo.h
index d2639cb271d..3766ed45b8c 100644
--- a/llvm/lib/Target/SystemZ/SystemZTargetTransformInfo.h
+++ b/llvm/lib/Target/SystemZ/SystemZTargetTransformInfo.h
@@ -55,6 +55,7 @@ public:
   unsigned getNumberOfRegisters(bool Vector);
   unsigned getRegisterBitWidth(bool Vector);
 
+  bool supportsEfficientVectorElementLoadStore() { return true; }
   bool enableInterleavedAccessVectorization() { return true; }
 
   int getArithmeticInstrCost(
diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
index f891cd9d62c..26bcbcb5f18 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -3663,13 +3663,17 @@ static unsigned getScalarizationOverhead(Instruction *I, unsigned VF,
 
   unsigned Cost = 0;
   Type *RetTy = ToVectorTy(I->getType(), VF);
-  if (!RetTy->isVoidTy())
+  if (!RetTy->isVoidTy() &&
+      (!isa<LoadInst>(I) ||
+       !TTI.supportsEfficientVectorElementLoadStore()))
     Cost += TTI.getScalarizationOverhead(RetTy, true, false);
 
   if (CallInst *CI = dyn_cast<CallInst>(I)) {
     SmallVector<const Value *, 4> Operands(CI->arg_operands());
     Cost += TTI.getOperandsScalarizationOverhead(Operands, VF);
-  } else {
+  }
+  else if (!isa<StoreInst>(I) ||
+           !TTI.supportsEfficientVectorElementLoadStore()) {
     SmallVector<const Value *, 4> Operands(I->operand_values());
     Cost += TTI.getOperandsScalarizationOverhead(Operands, VF);
   }