[ARM] Mark VMOVDRR with the RegSequence property and implement the related

target hook.

This patch teaches the compiler that:
dX = VMOVDRR rY, rZ
is the same as:
dX = REG_SEQUENCE rY, ssub_0, rZ, ssub_1

<rdar://problem/12702965>

llvm-svn: 215404

lib/Target/ARM/ARMInstrInfo.cpp

@@ -98,6 +98,31 @@ void ARMInstrInfo::expandLoadStackGuard(MachineBasicBlock::iterator MI,
     expandLoadStackGuardBase(MI, ARM::LDRLIT_ga_abs, ARM::LDRi12, RM);
 }
 
+bool ARMInstrInfo::getRegSequenceLikeInputs(
+    const MachineInstr &MI, unsigned DefIdx,
+    SmallVectorImpl<RegSubRegPairAndIdx> &InputRegs) const {
+  assert(DefIdx < MI.getDesc().getNumDefs() && "Invalid definition index");
+  assert(MI.isRegSequenceLike() && "Invalid kind of instruction");
+
+  switch (MI.getOpcode()) {
+  case ARM::VMOVDRR:
+    // dX = VMOVDRR rY, rZ
+    // is the same as:
+    // dX = REG_SEQUENCE rY, ssub_0, rZ, ssub_1
+    // Populate the InputRegs accordingly.
+    // rY
+    const MachineOperand *MOReg = &MI.getOperand(1);
+    InputRegs.push_back(
+        RegSubRegPairAndIdx(MOReg->getReg(), MOReg->getSubReg(), ARM::ssub_0));
+    // rZ
+    MOReg = &MI.getOperand(2);
+    InputRegs.push_back(
+        RegSubRegPairAndIdx(MOReg->getReg(), MOReg->getSubReg(), 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.

lib/Target/ARM/ARMInstrInfo.h

@@ -38,6 +38,23 @@ public:
   ///
   const ARMRegisterInfo &getRegisterInfo() const override { return RI; }
 
+  /// Build the equivalent inputs of a REG_SEQUENCE for the given \p MI
+  /// and \p DefIdx.
+  /// \p [out] InputRegs of the equivalent REG_SEQUENCE. Each element of
+  /// the list is modeled as <Reg:SubReg, SubIdx>.
+  /// E.g., REG_SEQUENCE vreg1:sub1, sub0, vreg2, sub1 would produce
+  /// two elements:
+  /// - vreg1:sub1, sub0
+  /// - vreg2<:0>, sub1
+  ///
+  /// \returns true if it is possible to build such an input sequence
+  /// with the pair \p MI, \p DefIdx. False otherwise.
+  ///
+  /// \pre MI.isRegSequenceLike().
+  bool getRegSequenceLikeInputs(
+      const MachineInstr &MI, unsigned DefIdx,
+      SmallVectorImpl<RegSubRegPairAndIdx> &InputRegs) const override;
+
 private:
   void expandLoadStackGuard(MachineBasicBlock::iterator MI,
                             Reloc::Model RM) const override;

lib/Target/ARM/ARMInstrVFP.td

@@ -885,6 +885,10 @@ def VMOVDRR : AVConv5I<0b11000100, 0b1011,
   // Some single precision VFP instructions may be executed on both NEON and VFP
   // pipelines.
   let D = VFPNeonDomain;
+
+  // This instruction is equivalent to
+  // $Dm = REG_SEQUENCE $Rt, ssub_0, $Rt2, ssub_1
+  let isRegSequence = 1;
 }
 
 let neverHasSideEffects = 1 in