[LV] Introduce TTI::getMinimumVF

The function getMinimumVF(ElemWidth) will return the minimum VF for
a vector with elements of size ElemWidth bits. This value will only
apply to targets for which TTI::shouldMaximizeVectorBandwidth returns
true. The value of 0 indicates that there is no minimum VF.

Differential Revision: https://reviews.llvm.org/D45271

llvm-svn: 330062

4 files changed, 16 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/TargetTransformInfo.cpp b/llvm/lib/Analysis/TargetTransformInfo.cpp
index 7744dbd8ca9..9843eed4c5a 100644
--- a/llvm/lib/Analysis/TargetTransformInfo.cpp
+++ b/llvm/lib/Analysis/TargetTransformInfo.cpp
@@ -344,6 +344,10 @@ bool TargetTransformInfo::shouldMaximizeVectorBandwidth(bool OptSize) const {
   return TTIImpl->shouldMaximizeVectorBandwidth(OptSize);
 }
 
+unsigned TargetTransformInfo::getMinimumVF(unsigned ElemWidth) const {
+  return TTIImpl->getMinimumVF(ElemWidth);
+}
+
 bool TargetTransformInfo::shouldConsiderAddressTypePromotion(
     const Instruction &I, bool &AllowPromotionWithoutCommonHeader) const {
   return TTIImpl->shouldConsiderAddressTypePromotion(
diff --git a/llvm/lib/Target/Hexagon/HexagonTargetTransformInfo.cpp b/llvm/lib/Target/Hexagon/HexagonTargetTransformInfo.cpp
index d5401a277b6..764e8b8b788 100644
--- a/llvm/lib/Target/Hexagon/HexagonTargetTransformInfo.cpp
+++ b/llvm/lib/Target/Hexagon/HexagonTargetTransformInfo.cpp
@@ -76,6 +76,10 @@ unsigned HexagonTTIImpl::getMinVectorRegisterBitWidth() const {
   return getST()->useHVXOps() ? getST()->getVectorLength()*8 : 0;
 }
 
+unsigned HexagonTTIImpl::getMinimumVF(unsigned ElemWidth) const {
+  return (8 * getST()->getVectorLength()) / ElemWidth;
+}
+
 unsigned HexagonTTIImpl::getMemoryOpCost(unsigned Opcode, Type *Src,
       unsigned Alignment, unsigned AddressSpace, const Instruction *I) {
   if (Opcode == Instruction::Load && Src->isVectorTy()) {
diff --git a/llvm/lib/Target/Hexagon/HexagonTargetTransformInfo.h b/llvm/lib/Target/Hexagon/HexagonTargetTransformInfo.h
index 02324d7efc4..61ffdf64f9f 100644
--- a/llvm/lib/Target/Hexagon/HexagonTargetTransformInfo.h
+++ b/llvm/lib/Target/Hexagon/HexagonTargetTransformInfo.h
@@ -74,6 +74,7 @@ public:
   unsigned getRegisterBitWidth(bool Vector) const;
   unsigned getMinVectorRegisterBitWidth() const;
   bool shouldMaximizeVectorBandwidth(bool OptSize) const { return true; }
+  unsigned getMinimumVF(unsigned ElemWidth) const;
 
   bool supportsEfficientVectorElementLoadStore() {
     return false;
diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
index 51be86ff337..fa736610cf5 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -6143,6 +6143,13 @@ LoopVectorizationCostModel::computeFeasibleMaxVF(bool OptForSize,
         break;
       }
     }
+    if (unsigned MinVF = TTI.getMinimumVF(SmallestType)) {
+      if (MaxVF < MinVF) {
+        DEBUG(dbgs() << "LV: Overriding calculated MaxVF(" << MaxVF
+                     << ") with target's minimum: " << MinVF << '\n');
+        MaxVF = MinVF;
+      }
+    }
   }
   return MaxVF;
 }