[PATCH] D11108: [TTI] BasicTTIImpl assumes no vector registers

[Jingyue Wu]

jingyue created this revision.
jingyue added a reviewer: hfinkel.
jingyue added subscribers: jholewinski, llvm-commits.

Following the discussion on r241884, it's more reasonable to assume that a
target has no vector registers by default instead of letting every such
target overrides getNumberOfRegisters.

Therefore, this patch modifies BasicTTIImpl::getNumberOfRegisters to
return 0 when Vector is true, and partially reverts r241884 which
modifies NVPTXTTIImpl::getNumberOfRegisters.

It also fixes a performance bug in LoopVectorizer. Even if a target has
no vector registers, vectorization may still help ILP. So, we need both
checks to be false before disabling loop vectorization all together.

http://reviews.llvm.org/D11108

Files:
  include/llvm/CodeGen/BasicTTIImpl.h
  lib/Target/NVPTX/NVPTXTargetTransformInfo.cpp
  lib/Target/NVPTX/NVPTXTargetTransformInfo.h
  lib/Transforms/Vectorize/LoopVectorize.cpp

Index: lib/Transforms/Vectorize/LoopVectorize.cpp
===================================================================
--- lib/Transforms/Vectorize/LoopVectorize.cpp
+++ lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -1456,9 +1456,14 @@
     const BranchProbability ColdProb(1, 5); // 20%
     ColdEntryFreq = BlockFrequency(BFI->getEntryFreq()) * ColdProb;
 
-    // If the target claims to have no vector registers don't attempt
-    // vectorization.
-    if (!TTI->getNumberOfRegisters(true))
+    // Don't attempt if
+    // 1. the target claims to have no vector registers, and
+    // 2. interleaving won't help ILP.
+    //
+    // The second condition is necessary because, even if the target has no
+    // vector registers, loop vectorization may still enable scalar
+    // interleaving.
+    if (!TTI->getNumberOfRegisters(true) && TTI->getMaxInterleaveFactor(1) < 2)
       return false;
 
     // Build up a worklist of inner-loops to vectorize. This is necessary as
Index: lib/Target/NVPTX/NVPTXTargetTransformInfo.h
===================================================================
--- lib/Target/NVPTX/NVPTXTargetTransformInfo.h
+++ lib/Target/NVPTX/NVPTXTargetTransformInfo.h
@@ -58,8 +58,6 @@
       TTI::OperandValueKind Opd2Info = TTI::OK_AnyValue,
       TTI::OperandValueProperties Opd1PropInfo = TTI::OP_None,
       TTI::OperandValueProperties Opd2PropInfo = TTI::OP_None);
-
-  unsigned getNumberOfRegisters(bool Vector);
 };
 
 } // end namespace llvm
Index: lib/Target/NVPTX/NVPTXTargetTransformInfo.cpp
===================================================================
--- lib/Target/NVPTX/NVPTXTargetTransformInfo.cpp
+++ lib/Target/NVPTX/NVPTXTargetTransformInfo.cpp
@@ -117,9 +117,3 @@
                                          Opd1PropInfo, Opd2PropInfo);
   }
 }
-
-unsigned NVPTXTTIImpl::getNumberOfRegisters(bool Vector) {
-  if (Vector)
-    return 0;
-  return BaseT::getNumberOfRegisters(Vector);
-}
Index: include/llvm/CodeGen/BasicTTIImpl.h
===================================================================
--- include/llvm/CodeGen/BasicTTIImpl.h
+++ include/llvm/CodeGen/BasicTTIImpl.h
@@ -276,7 +276,7 @@
   /// \name Vector TTI Implementations
   /// @{
 
-  unsigned getNumberOfRegisters(bool Vector) { return 1; }
+  unsigned getNumberOfRegisters(bool Vector) { return Vector ? 0 : 1; }
 
   unsigned getRegisterBitWidth(bool Vector) { return 32; }
 


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