[X86][ARM][TargetLowering] Add SrcVT to isExtractSubvectorCheap

[craig.topper]

Summary

Without the SrcVT its hard to know what is really being asked for. For example if your target has 128, 256, and 512 bit vectors. Maybe extracting 128 from 256 is cheap, but maybe extracting 128 from 512 is not.

For x86 we do support extracting a quarter of a 512-bit register. But for i1 vectors we don't have isel patterns for extracting arbitrary pieces. So we need this to have a correct implementation of isExtractSubvectorCheap for mask vectors.

[RKSimon]

LGTM - one minor

include/llvm/Target/TargetLowering.h

2179 ↗

(On Diff #110858)

Update comment to describe ResVT and SrcVT

llvm/trunk/include/llvm/Target/TargetLowering.h

public:
   /// On some targets it might be more efficient to use a combination of
   /// arithmetic instructions to materialize the constant instead of loading it
   /// from a constant pool.
   virtual bool shouldConvertConstantLoadToIntImm(const APInt &Imm,
                                                  Type *Ty) const {
     return false;
   }
 
-  /// Return true if EXTRACT_SUBVECTOR is cheap for this result type
-  /// with this index. This is needed because EXTRACT_SUBVECTOR usually
-  /// has custom lowering that depends on the index of the first element,
-  /// and only the target knows which lowering is cheap.
-  virtual bool isExtractSubvectorCheap(EVT ResVT, unsigned Index) const {
+  /// Return true if EXTRACT_SUBVECTOR is cheap for extracting this result type
+  /// from this source type with this index. This is needed because
+  /// EXTRACT_SUBVECTOR usually has custom lowering that depends on the index of
+  /// the first element, and only the target knows which lowering is cheap.
+  virtual bool isExtractSubvectorCheap(EVT ResVT, EVT SrcVT,
+                                       unsigned Index) const {
     return false;
   }
 
   // Return true if it is profitable to use a scalar input to a BUILD_VECTOR
   // even if the vector itself has multiple uses.
   virtual bool aggressivelyPreferBuildVectorSources(EVT VecVT) const {
     return false;
   }

llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

if ((VT.getSizeInBits() % InVT1.getSizeInBits() == 0) && InVT1 == InVT2) {
       unsigned NumConcats = VT.getSizeInBits() / InVT1.getSizeInBits();
       assert(NumConcats >= 2 && "Concat needs at least two inputs!");
       SmallVector<SDValue, 2> ConcatOps(NumConcats, DAG.getUNDEF(InVT1));
       ConcatOps[0] = VecIn1;
       ConcatOps[1] = VecIn2 ? VecIn2 : DAG.getUNDEF(InVT1);
       VecIn1 = DAG.getNode(ISD::CONCAT_VECTORS, DL, VT, ConcatOps);
       VecIn2 = SDValue();
     } else if (InVT1.getSizeInBits() == VT.getSizeInBits() * 2) {
-      if (!TLI.isExtractSubvectorCheap(VT, NumElems))
+      if (!TLI.isExtractSubvectorCheap(VT, InVT1, NumElems))
         return SDValue();
 
       if (!VecIn2.getNode()) {
         // If we only have one input vector, and it's twice the size of the
         // output, split it in two.
         VecIn2 = DAG.getNode(ISD::EXTRACT_SUBVECTOR, DL, VT, VecIn1,
                              DAG.getConstant(NumElems, DL, IdxTy));
         VecIn1 = DAG.getNode(ISD::EXTRACT_SUBVECTOR, DL, VT, VecIn1, ZeroIdx);

llvm/trunk/lib/Target/ARM/ARMISelLowering.h

public:
 
     /// \brief Returns true if it is beneficial to convert a load of a constant
     /// to just the constant itself.
     bool shouldConvertConstantLoadToIntImm(const APInt &Imm,
                                            Type *Ty) const override;
 
     /// Return true if EXTRACT_SUBVECTOR is cheap for this result type
     /// with this index.
-    bool isExtractSubvectorCheap(EVT ResVT, unsigned Index) const override;
+    bool isExtractSubvectorCheap(EVT ResVT, EVT SrcVT,
+                                 unsigned Index) const override;
 
     /// \brief Returns true if an argument of type Ty needs to be passed in a
     /// contiguous block of registers in calling convention CallConv.
     bool functionArgumentNeedsConsecutiveRegisters(
         Type *Ty, CallingConv::ID CallConv, bool isVarArg) const override;
 
     /// If a physical register, this returns the register that receives the
     /// exception address on entry to an EH pad.

llvm/trunk/lib/Target/ARM/ARMISelLowering.cpp

bool ARMTargetLowering::shouldConvertConstantLoadToIntImm(const APInt &Imm,
   assert(Ty->isIntegerTy());
 
   unsigned Bits = Ty->getPrimitiveSizeInBits();
   if (Bits == 0 || Bits > 32)
     return false;
   return true;
 }
 
-bool ARMTargetLowering::isExtractSubvectorCheap(EVT ResVT,
+bool ARMTargetLowering::isExtractSubvectorCheap(EVT ResVT, EVT SrcVT,
                                                 unsigned Index) const {
   if (!isOperationLegalOrCustom(ISD::EXTRACT_SUBVECTOR, ResVT))
     return false;
 
   return (Index == 0 || Index == ResVT.getVectorNumElements());
 }
 
 Instruction* ARMTargetLowering::makeDMB(IRBuilder<> &Builder,

llvm/trunk/lib/Target/X86/X86ISelLowering.h

bool shouldConvertConstantLoadToIntImm(const APInt &Imm,
                                            Type *Ty) const override;
 
     bool convertSelectOfConstantsToMath() const override {
       return true;
     }
 
     /// Return true if EXTRACT_SUBVECTOR is cheap for this result type
     /// with this index.
-    bool isExtractSubvectorCheap(EVT ResVT, unsigned Index) const override;
+    bool isExtractSubvectorCheap(EVT ResVT, EVT SrcVT,
+                                 unsigned Index) const override;
 
     /// Intel processors have a unified instruction and data cache
     const char * getClearCacheBuiltinName() const override {
       return nullptr; // nothing to do, move along.
     }
 
     unsigned getRegisterByName(const char* RegName, EVT VT,
                                SelectionDAG &DAG) const override;

llvm/trunk/lib/Target/X86/X86ISelLowering.cpp

bool X86TargetLowering::shouldConvertConstantLoadToIntImm(const APInt &Imm,
   assert(Ty->isIntegerTy());
 
   unsigned BitSize = Ty->getPrimitiveSizeInBits();
   if (BitSize == 0 || BitSize > 64)
     return false;
   return true;
 }
 
-bool X86TargetLowering::isExtractSubvectorCheap(EVT ResVT,
+bool X86TargetLowering::isExtractSubvectorCheap(EVT ResVT, EVT SrcVT,
                                                 unsigned Index) const {
   if (!isOperationLegalOrCustom(ISD::EXTRACT_SUBVECTOR, ResVT))
     return false;
 
   return (Index == 0 || Index == ResVT.getVectorNumElements());
 }
 
 bool X86TargetLowering::isCheapToSpeculateCttz() const {