[llvm-commits] [llvm] r173621 - BBVectorize: Better use of TTI->getShuffleCost

[Hal Finkel]

Author: hfinkel
Date: Sun Jan 27 14:07:01 2013
New Revision: 173621

URL: http://llvm.org/viewvc/llvm-project?rev=173621&view=rev
Log:
BBVectorize: Better use of TTI->getShuffleCost

When flipping the pair of subvectors that form a vector, if the
vector length is 2, we can use the SK_Reverse shuffle kind to get
more-accurate cost information. Also we can use the SK_ExtractSubvector
shuffle kind to get accurate subvector extraction costs.

The current cost model implementations don't yet seem complex enough
for this to make a difference (thus, there are no test cases with this
commit), but it should help in future.

Depending on how the various targets optimize and combine shuffles in
practice, we might be able to get more-accurate costs by combining the
costs of multiple shuffle kinds. For example, the cost of flipping the
subvector pairs could be modeled as two extractions and two subvector
insertions. These changes, however, should probably be motivated
by specific test cases.

Modified:
    llvm/trunk/lib/Transforms/Vectorize/BBVectorize.cpp

Modified: llvm/trunk/lib/Transforms/Vectorize/BBVectorize.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Vectorize/BBVectorize.cpp?rev=173621&r1=173620&r2=173621&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Vectorize/BBVectorize.cpp (original)
+++ llvm/trunk/lib/Transforms/Vectorize/BBVectorize.cpp Sun Jan 27 14:07:01 2013
@@ -1824,6 +1824,16 @@ namespace {
                   R->second == PairConnectionSplat) {
                 int ESContrib = (int) getInstrCost(Instruction::ShuffleVector,
                                                    VTy, VTy);
+
+                if (VTy->getVectorNumElements() == 2) {
+                  if (R->second == PairConnectionSplat)
+                    ESContrib = std::min(ESContrib, (int) TTI->getShuffleCost(
+                      TargetTransformInfo::SK_Broadcast, VTy));
+                  else
+                    ESContrib = std::min(ESContrib, (int) TTI->getShuffleCost(
+                      TargetTransformInfo::SK_Reverse, VTy));
+                }
+
                 DEBUG(if (DebugPairSelection) dbgs() << "\tcost {" <<
                   *Q->second.first << " <-> " << *Q->second.second <<
                     "} -> {" <<
@@ -1860,10 +1870,12 @@ namespace {
 
             if (NeedsExtraction) {
               int ESContrib;
-              if (Ty1->isVectorTy())
+              if (Ty1->isVectorTy()) {
                 ESContrib = (int) getInstrCost(Instruction::ShuffleVector,
                                                Ty1, VTy);
-              else
+                ESContrib = std::min(ESContrib, (int) TTI->getShuffleCost(
+                  TargetTransformInfo::SK_ExtractSubvector, VTy, 0, Ty1));
+              } else
                 ESContrib = (int) TTI->getVectorInstrCost(
                                     Instruction::ExtractElement, VTy, 0);
 
@@ -1890,10 +1902,13 @@ namespace {
 
             if (NeedsExtraction) {
               int ESContrib;
-              if (Ty2->isVectorTy())
+              if (Ty2->isVectorTy()) {
                 ESContrib = (int) getInstrCost(Instruction::ShuffleVector,
                                                Ty2, VTy);
-              else
+                ESContrib = std::min(ESContrib, (int) TTI->getShuffleCost(
+                  TargetTransformInfo::SK_ExtractSubvector, VTy,
+                  Ty1->isVectorTy() ? Ty1->getVectorNumElements() : 1, Ty2));
+              } else
                 ESContrib = (int) TTI->getVectorInstrCost(
                                     Instruction::ExtractElement, VTy, 1);
               DEBUG(if (DebugPairSelection) dbgs() << "\tcost {" <<
@@ -1969,6 +1984,10 @@ namespace {
               } else if (IncomingPairs.count(VPR)) {
                 ESContrib = (int) getInstrCost(Instruction::ShuffleVector,
                                                VTy, VTy);
+
+                if (VTy->getVectorNumElements() == 2)
+                  ESContrib = std::min(ESContrib, (int) TTI->getShuffleCost(
+                    TargetTransformInfo::SK_Reverse, VTy));
               } else if (!Ty1->isVectorTy() && !Ty2->isVectorTy()) {
                 ESContrib = (int) TTI->getVectorInstrCost(
                                     Instruction::InsertElement, VTy, 0);