Currently isLikelyComplexAddressComputation tries to figure out if the given stride seems to be 'complex' and need some extra cost for address computation handling.

This code seems to be target dependent which may not be the same for all targets.
Passed the decision whether the given stride is complex or not to the target by sending stride information via SCEV to getAddressComputationCost instead of 'IsComplex'.

Specifically at X86 targets we dont see any significant address computation cost in case of the strided access in general.

Differential Revision: https://reviews.llvm.org/D27518

llvm-svn: 291106

1 files changed, 17 insertions, 42 deletions

diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
index 8cde0c4cd60..31daba2248a 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -6785,22 +6785,19 @@ LoopVectorizationCostModel::expectedCost(unsigned VF) {
   return Cost;
 }
 
-/// \brief Check whether the address computation for a non-consecutive memory
-/// access looks like an unlikely candidate for being merged into the indexing
-/// mode.
+/// \brief Gets Address Access SCEV after verifying that the access pattern
+/// is loop invariant except the induction variable dependence.
 ///
-/// We look for a GEP which has one index that is an induction variable and all
-/// other indices are loop invariant. If the stride of this access is also
-/// within a small bound we decide that this address computation can likely be
-/// merged into the addressing mode.
-/// In all other cases, we identify the address computation as complex.
-static bool isLikelyComplexAddressComputation(Value *Ptr,
-                                              LoopVectorizationLegality *Legal,
-                                              ScalarEvolution *SE,
-                                              const Loop *TheLoop) {
+/// This SCEV can be sent to the Target in order to estimate the address
+/// calculation cost.
+static const SCEV *getAddressAccessSCEV(
+              Value *Ptr,
+              LoopVectorizationLegality *Legal,
+              ScalarEvolution *SE,
+              const Loop *TheLoop) {
   auto *Gep = dyn_cast<GetElementPtrInst>(Ptr);
   if (!Gep)
-    return true;
+    return nullptr;
 
   // We are looking for a gep with all loop invariant indices except for one
   // which should be an induction variable.
@@ -6809,33 +6806,11 @@ static bool isLikelyComplexAddressComputation(Value *Ptr,
     Value *Opd = Gep->getOperand(i);
     if (!SE->isLoopInvariant(SE->getSCEV(Opd), TheLoop) &&
         !Legal->isInductionVariable(Opd))
-      return true;
+      return nullptr;
   }
 
-  // Now we know we have a GEP ptr, %inv, %ind, %inv. Make sure that the step
-  // can likely be merged into the address computation.
-  unsigned MaxMergeDistance = 64;
-
-  const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(Ptr));
-  if (!AddRec)
-    return true;
-
-  // Check the step is constant.
-  const SCEV *Step = AddRec->getStepRecurrence(*SE);
-  // Calculate the pointer stride and check if it is consecutive.
-  const auto *C = dyn_cast<SCEVConstant>(Step);
-  if (!C)
-    return true;
-
-  const APInt &APStepVal = C->getAPInt();
-
-  // Huge step value - give up.
-  if (APStepVal.getBitWidth() > 64)
-    return true;
-
-  int64_t StepVal = APStepVal.getSExtValue();
-
-  return StepVal > MaxMergeDistance;
+  // Now we know we have a GEP ptr, %inv, %ind, %inv. return the Ptr SCEV.
+  return SE->getSCEV(Ptr);
 }
 
 static bool isStrideMul(Instruction *I, LoopVectorizationLegality *Legal) {
@@ -7063,12 +7038,12 @@ unsigned LoopVectorizationCostModel::getInstructionCost(Instruction *I,
       unsigned Cost = 0;
       Type *PtrTy = ToVectorTy(Ptr->getType(), VF);
 
-      // True if the memory instruction's address computation is complex.
-      bool IsComplexComputation =
-          isLikelyComplexAddressComputation(Ptr, Legal, SE, TheLoop);
+      // Figure out whether the access is strided and get the stride value
+      // if it's known in compile time
+      const SCEV *PtrSCEV = getAddressAccessSCEV(Ptr, Legal, SE, TheLoop); 
 
       // Get the cost of the scalar memory instruction and address computation.
-      Cost += VF * TTI.getAddressComputationCost(PtrTy, IsComplexComputation);
+      Cost += VF * TTI.getAddressComputationCost(PtrTy, SE, PtrSCEV);
       Cost += VF *
               TTI.getMemoryOpCost(I->getOpcode(), ValTy->getScalarType(),
                                   Alignment, AS);