[ARM] Mark VMOVRRD with the ExtractSubreg property and implement the related

target hook.

This patch teaches the compiler that:
rX, rY = VMOVRRD dZ
is the same as:
rX = EXTRACT_SUBREG dZ, ssub_0
rY = EXTRACT_SUBREG dZ, ssub_1

<rdar://problem/12702965>

llvm-svn: 216132

llvm/lib/Target/ARM/ARMInstrInfo.cpp

@@ -123,6 +123,27 @@ bool ARMInstrInfo::getRegSequenceLikeInputs(
   llvm_unreachable("Target dependent opcode missing");
 }
 
+bool ARMInstrInfo::getExtractSubregLikeInputs(
+    const MachineInstr &MI, unsigned DefIdx,
+    RegSubRegPairAndIdx &InputReg) const {
+  assert(DefIdx < MI.getDesc().getNumDefs() && "Invalid definition index");
+  assert(MI.isExtractSubregLike() && "Invalid kind of instruction");
+
+  switch (MI.getOpcode()) {
+  case ARM::VMOVRRD:
+    // rX, rY = VMOVRRD dZ
+    // is the same as:
+    // rX = EXTRACT_SUBREG dZ, ssub_0
+    // rY = EXTRACT_SUBREG dZ, ssub_1
+    const MachineOperand &MOReg = MI.getOperand(2);
+    InputReg.Reg = MOReg.getReg();
+    InputReg.SubReg = MOReg.getSubReg();
+    InputReg.SubIdx = DefIdx == 0 ? ARM::ssub_0 : ARM::ssub_1;
+    return true;
+  }
+  llvm_unreachable("Target dependent opcode missing");
+}
+
 namespace {
   /// ARMCGBR - Create Global Base Reg pass. This initializes the PIC
   /// global base register for ARM ELF.

llvm/lib/Target/ARM/ARMInstrInfo.h

@@ -55,6 +55,19 @@ public:
       const MachineInstr &MI, unsigned DefIdx,
       SmallVectorImpl<RegSubRegPairAndIdx> &InputRegs) const override;
 
+  /// Build the equivalent inputs of a EXTRACT_SUBREG for the given \p MI
+  /// and \p DefIdx.
+  /// \p [out] InputReg of the equivalent EXTRACT_SUBREG.
+  /// E.g., EXTRACT_SUBREG vreg1:sub1, sub0, sub1 would produce:
+  /// - vreg1:sub1, sub0
+  ///
+  /// \returns true if it is possible to build such an input sequence
+  /// with the pair \p MI, \p DefIdx. False otherwise.
+  ///
+  /// \pre MI.isExtractSubregLike().
+  bool getExtractSubregLikeInputs(const MachineInstr &MI, unsigned DefIdx,
+                                  RegSubRegPairAndIdx &InputReg) const override;
+
 private:
   void expandLoadStackGuard(MachineBasicBlock::iterator MI,
                             Reloc::Model RM) const override;

llvm/lib/Target/ARM/ARMInstrVFP.td

@@ -842,6 +842,11 @@ def VMOVRRD  : AVConv3I<0b11000101, 0b1011,
   // Some single precision VFP instructions may be executed on both NEON and VFP
   // pipelines.
   let D = VFPNeonDomain;
+
+  // This instruction is equivalent to
+  // $Rt = EXTRACT_SUBREG $Dm, ssub_0
+  // $Rt2 = EXTRACT_SUBREG $Dm, ssub_1
+  let isExtractSubreg = 1;
 }
 
 def VMOVRRS  : AVConv3I<0b11000101, 0b1010,