Recommit "[GlobalISel][AArch64] Add selection support for G_EXTRACT_VECTOR_ELT"

After r355865, we should be able to safely select G_EXTRACT_VECTOR_ELT without
running into any problematic intrinsics.

Also add a fix for lane copies, which don't support index 0.

llvm-svn: 355871

3 files changed, 146 insertions, 18 deletions

diff --git a/llvm/lib/Target/AArch64/AArch64InstructionSelector.cpp b/llvm/lib/Target/AArch64/AArch64InstructionSelector.cpp
index 41f4eb9563a..869cc143496 100644
--- a/llvm/lib/Target/AArch64/AArch64InstructionSelector.cpp
+++ b/llvm/lib/Target/AArch64/AArch64InstructionSelector.cpp
@@ -78,6 +78,7 @@ private:
   void collectShuffleMaskIndices(MachineInstr &I, MachineRegisterInfo &MRI,
                                  SmallVectorImpl<int> &Idxs) const;
   bool selectShuffleVector(MachineInstr &I, MachineRegisterInfo &MRI) const;
+  bool selectExtractElt(MachineInstr &I, MachineRegisterInfo &MRI) const;
 
   unsigned emitConstantPoolEntry(Constant *CPVal, MachineFunction &MF) const;
   MachineInstr *emitLoadFromConstantPool(Constant *CPVal,
@@ -1709,6 +1710,8 @@ bool AArch64InstructionSelector::select(MachineInstr &I,
     return selectUnmergeValues(I, MRI);
   case TargetOpcode::G_SHUFFLE_VECTOR:
     return selectShuffleVector(I, MRI);
+  case TargetOpcode::G_EXTRACT_VECTOR_ELT:
+    return selectExtractElt(I, MRI);
   }
 
   return false;
@@ -1787,6 +1790,138 @@ bool AArch64InstructionSelector::selectMergeValues(
   return true;
 }
 
+static bool getLaneCopyOpcode(unsigned &CopyOpc, unsigned &ExtractSubReg,
+                              const unsigned EltSize) {
+  // Choose a lane copy opcode and subregister based off of the size of the
+  // vector's elements.
+  switch (EltSize) {
+  case 16:
+    CopyOpc = AArch64::CPYi16;
+    ExtractSubReg = AArch64::hsub;
+    break;
+  case 32:
+    CopyOpc = AArch64::CPYi32;
+    ExtractSubReg = AArch64::ssub;
+    break;
+  case 64:
+    CopyOpc = AArch64::CPYi64;
+    ExtractSubReg = AArch64::dsub;
+    break;
+  default:
+    // Unknown size, bail out.
+    LLVM_DEBUG(dbgs() << "Elt size '" << EltSize << "' unsupported.\n");
+    return false;
+  }
+  return true;
+}
+
+bool AArch64InstructionSelector::selectExtractElt(
+    MachineInstr &I, MachineRegisterInfo &MRI) const {
+  assert(I.getOpcode() == TargetOpcode::G_EXTRACT_VECTOR_ELT &&
+         "unexpected opcode!");
+  unsigned DstReg = I.getOperand(0).getReg();
+  const LLT NarrowTy = MRI.getType(DstReg);
+  const unsigned SrcReg = I.getOperand(1).getReg();
+  const LLT WideTy = MRI.getType(SrcReg);
+
+  assert(WideTy.getSizeInBits() >= NarrowTy.getSizeInBits() &&
+         "source register size too small!");
+  assert(NarrowTy.isScalar() && "cannot extract vector into vector!");
+
+  // Need the lane index to determine the correct copy opcode.
+  MachineOperand &LaneIdxOp = I.getOperand(2);
+  assert(LaneIdxOp.isReg() && "Lane index operand was not a register?");
+
+  if (RBI.getRegBank(DstReg, MRI, TRI)->getID() != AArch64::FPRRegBankID) {
+    LLVM_DEBUG(dbgs() << "Cannot extract into GPR.\n");
+    return false;
+  }
+
+  // Find the instruction that defines the constant to extract from. There could
+  // be any number of copies between the instruction and the definition of the
+  // index. Skip them.
+  MachineInstr *LaneDefInst = nullptr;
+  for (LaneDefInst = MRI.getVRegDef(LaneIdxOp.getReg());
+       LaneDefInst && LaneDefInst->isCopy();
+       LaneDefInst = MRI.getVRegDef(LaneDefInst->getOperand(1).getReg())) {
+  }
+
+  // Did we find a def in the first place? If not, bail.
+  if (!LaneDefInst) {
+    LLVM_DEBUG(dbgs() << "Did not find VReg definition for " << LaneIdxOp
+                      << "\n");
+    return false;
+  }
+
+  // TODO: Handle extracts that don't use G_CONSTANT.
+  if (LaneDefInst->getOpcode() != TargetOpcode::G_CONSTANT) {
+    LLVM_DEBUG(dbgs() << "VRegs defined by anything other than G_CONSTANT "
+                         "currently unsupported.\n");
+    return false;
+  }
+
+  unsigned LaneIdx = LaneDefInst->getOperand(1).getCImm()->getLimitedValue();
+  unsigned CopyOpc = 0;
+  unsigned ExtractSubReg = 0;
+  if (!getLaneCopyOpcode(CopyOpc, ExtractSubReg, NarrowTy.getSizeInBits())) {
+    LLVM_DEBUG(
+        dbgs() << "Couldn't determine lane copy opcode for instruction.\n");
+    return false;
+  }
+
+  const RegisterBank &DstRB = *RBI.getRegBank(DstReg, MRI, TRI);
+  const TargetRegisterClass *DstRC =
+      getRegClassForTypeOnBank(NarrowTy, DstRB, RBI, true);
+  if (!DstRC) {
+    LLVM_DEBUG(dbgs() << "Could not determine destination register class.\n");
+    return false;
+  }
+
+  const RegisterBank &SrcRB = *RBI.getRegBank(SrcReg, MRI, TRI);
+  const TargetRegisterClass *SrcRC =
+      getRegClassForTypeOnBank(WideTy, SrcRB, RBI, true);
+  if (!SrcRC) {
+    LLVM_DEBUG(dbgs() << "Could not determine source register class.\n");
+    return false;
+  }
+
+  // The register that we're going to copy into.
+  unsigned InsertReg = SrcReg;
+  MachineIRBuilder MIRBuilder(I);
+
+  // If the lane index is 0, we just use a subregister COPY.
+  if (LaneIdx == 0) {
+    unsigned CopyTo = I.getOperand(0).getReg();
+    BuildMI(*I.getParent(), I, I.getDebugLoc(), TII.get(TargetOpcode::COPY),
+            CopyTo)
+        .addUse(SrcReg, 0, ExtractSubReg);
+    RBI.constrainGenericRegister(CopyTo, *DstRC, MRI);
+    I.eraseFromParent();
+    return true;
+  }
+
+  // Lane copies require 128-bit wide registers. If we're dealing with an
+  // unpacked vector, then we need to move up to that width. Insert an implicit
+  // def and a subregister insert to get us there.
+  if (WideTy.getSizeInBits() != 128) {
+    MachineInstr *ScalarToVector = emitScalarToVector(
+        WideTy.getSizeInBits(), &AArch64::FPR128RegClass, SrcReg, MIRBuilder);
+    if (!ScalarToVector)
+      return false;
+    InsertReg = ScalarToVector->getOperand(0).getReg();
+  }
+
+  MachineInstr *LaneCopyMI =
+      MIRBuilder.buildInstr(CopyOpc, {DstReg}, {InsertReg}).addImm(LaneIdx);
+  constrainSelectedInstRegOperands(*LaneCopyMI, TII, TRI, RBI);
+
+  // Make sure that we actually constrain the initial copy.
+  RBI.constrainGenericRegister(DstReg, *DstRC, MRI);
+
+  I.eraseFromParent();
+  return true;
+}
+
 bool AArch64InstructionSelector::selectUnmergeValues(
     MachineInstr &I, MachineRegisterInfo &MRI) const {
   assert(I.getOpcode() == TargetOpcode::G_UNMERGE_VALUES &&
@@ -1823,24 +1958,8 @@ bool AArch64InstructionSelector::selectUnmergeValues(
   // vector's elements.
   unsigned CopyOpc = 0;
   unsigned ExtractSubReg = 0;
-  switch (NarrowTy.getSizeInBits()) {
-  case 16:
-    CopyOpc = AArch64::CPYi16;
-    ExtractSubReg = AArch64::hsub;
-    break;
-  case 32:
-    CopyOpc = AArch64::CPYi32;
-    ExtractSubReg = AArch64::ssub;
-    break;
-  case 64:
-    CopyOpc = AArch64::CPYi64;
-    ExtractSubReg = AArch64::dsub;
-    break;
-  default:
-    // Unknown size, bail out.
-    LLVM_DEBUG(dbgs() << "NarrowTy had unsupported size.\n");
+  if (!getLaneCopyOpcode(CopyOpc, ExtractSubReg, NarrowTy.getSizeInBits()))
     return false;
-  }
 
   // Set up for the lane copies.
   MachineBasicBlock &MBB = *I.getParent();
diff --git a/llvm/lib/Target/AArch64/AArch64LegalizerInfo.cpp b/llvm/lib/Target/AArch64/AArch64LegalizerInfo.cpp
index c473dc490c5..4a2f28117ec 100644
--- a/llvm/lib/Target/AArch64/AArch64LegalizerInfo.cpp
+++ b/llvm/lib/Target/AArch64/AArch64LegalizerInfo.cpp
@@ -446,7 +446,8 @@ AArch64LegalizerInfo::AArch64LegalizerInfo(const AArch64Subtarget &ST) {
       .minScalar(2, s64)
       .legalIf([=](const LegalityQuery &Query) {
         const LLT &VecTy = Query.Types[1];
-        return VecTy == v4s32 || VecTy == v2s64;
+        return VecTy == v2s16 || VecTy == v4s16 || VecTy == v4s32 ||
+               VecTy == v2s64 || VecTy == v2s32;
       });
 
   getActionDefinitionsBuilder(G_BUILD_VECTOR)
diff --git a/llvm/lib/Target/AArch64/AArch64RegisterBankInfo.cpp b/llvm/lib/Target/AArch64/AArch64RegisterBankInfo.cpp
index 08cf6859f05..e4aebf4dbfe 100644
--- a/llvm/lib/Target/AArch64/AArch64RegisterBankInfo.cpp
+++ b/llvm/lib/Target/AArch64/AArch64RegisterBankInfo.cpp
@@ -689,6 +689,14 @@ AArch64RegisterBankInfo::getInstrMapping(const MachineInstr &MI) const {
     }
     break;
   }
+  case TargetOpcode::G_EXTRACT_VECTOR_ELT:
+    // Destination and source need to be FPRs.
+    OpRegBankIdx[0] = PMI_FirstFPR;
+    OpRegBankIdx[1] = PMI_FirstFPR;
+
+    // Index needs to be a GPR.
+    OpRegBankIdx[2] = PMI_FirstGPR;
+    break;
 
   case TargetOpcode::G_BUILD_VECTOR:
     // If the first source operand belongs to a FPR register bank, then make