AMDGPU/SI: Factor operand folding code into its own function

[arsenm]

LGTM

lib/Target/AMDGPU/SIFoldOperands.cpp

if (!TII->isOperandLegal(MI, OpNo, OpToFold)) {
     if (!TII->isOperandLegal(MI, OpNo, OpToFold))
       return false;
   }
 
   FoldList.push_back(FoldCandidate(MI, OpNo, OpToFold));
   return true;
 }
 
-bool SIFoldOperands::runOnMachineFunction(MachineFunction &MF) {
-  MachineRegisterInfo &MRI = MF.getRegInfo();
-  const SIInstrInfo *TII =
-      static_cast<const SIInstrInfo *>(MF.getSubtarget().getInstrInfo());
-  const SIRegisterInfo &TRI = TII->getRegisterInfo();
-
-  for (MachineFunction::iterator BI = MF.begin(), BE = MF.end();
-                                                  BI != BE; ++BI) {
-
-    MachineBasicBlock &MBB = *BI;
-    MachineBasicBlock::iterator I, Next;
-    for (I = MBB.begin(); I != MBB.end(); I = Next) {
-      Next = std::next(I);
-      MachineInstr &MI = *I;
-
-      if (!isSafeToFold(MI.getOpcode()))
-        continue;
-
-      unsigned OpSize = TII->getOpSize(MI, 1);
-      MachineOperand &OpToFold = MI.getOperand(1);
-      bool FoldingImm = OpToFold.isImm();
-
-      // FIXME: We could also be folding things like FrameIndexes and
-      // TargetIndexes.
-      if (!FoldingImm && !OpToFold.isReg())
-        continue;
-
-      // Folding immediates with more than one use will increase program size.
-      // FIXME: This will also reduce register usage, which may be better
-      // in some cases.  A better heuristic is needed.
-      if (FoldingImm && !TII->isInlineConstant(OpToFold, OpSize) &&
-          !MRI.hasOneUse(MI.getOperand(0).getReg()))
-        continue;
-
-      // FIXME: Fold operands with subregs.
-      if (OpToFold.isReg() &&
-          (!TargetRegisterInfo::isVirtualRegister(OpToFold.getReg()) ||
-           OpToFold.getSubReg()))
-        continue;
-
-      std::vector<FoldCandidate> FoldList;
-      for (MachineRegisterInfo::use_iterator
-           Use = MRI.use_begin(MI.getOperand(0).getReg()), E = MRI.use_end();
-           Use != E; ++Use) {
-
-        MachineInstr *UseMI = Use->getParent();
-        const MachineOperand &UseOp = UseMI->getOperand(Use.getOperandNo());
+static void foldOperand(MachineOperand &OpToFold, MachineInstr *UseMI,
+                        unsigned UseOpIdx,
+                        std::vector<FoldCandidate> &FoldList,
+                        const SIInstrInfo *TII, const SIRegisterInfo &TRI,
+                        MachineRegisterInfo &MRI) {
+  const MachineOperand &UseOp = UseMI->getOperand(UseOpIdx);
 
-        // FIXME: Fold operands with subregs.
-        if (UseOp.isReg() && ((UseOp.getSubReg() && OpToFold.isReg()) ||
-            UseOp.isImplicit())) {
-          continue;
-        }
+    return;
 
-        APInt Imm;
+  bool FoldingImm = OpToFold.isImm();
 
-        if (FoldingImm) {
-          unsigned UseReg = UseOp.getReg();
-          const TargetRegisterClass *UseRC
-            = TargetRegisterInfo::isVirtualRegister(UseReg) ?
-            MRI.getRegClass(UseReg) :
-            TRI.getPhysRegClass(UseReg);
 
-          Imm = APInt(64, OpToFold.getImm());
 
-          // Split 64-bit constants into 32-bits for folding.
-          if (UseOp.getSubReg()) {
-            if (UseRC->getSize() != 8)
-              continue;
+        return;
 
-            if (UseOp.getSubReg() == AMDGPU::sub0) {
-              Imm = Imm.getLoBits(32);
-            } else {
-              assert(UseOp.getSubReg() == AMDGPU::sub1);
-              Imm = Imm.getHiBits(32);
-            }
-          }
 
-          // In order to fold immediates into copies, we need to change the
-          // copy to a MOV.
-          if (UseMI->getOpcode() == AMDGPU::COPY) {
-            unsigned DestReg = UseMI->getOperand(0).getReg();
-            const TargetRegisterClass *DestRC
-              = TargetRegisterInfo::isVirtualRegister(DestReg) ?
-              MRI.getRegClass(DestReg) :
-              TRI.getPhysRegClass(DestReg);
 
-            unsigned MovOp = TII->getMovOpcode(DestRC);
-            if (MovOp == AMDGPU::COPY)
-              continue;
+        return;
 
-            UseMI->setDesc(TII->get(MovOp));
-          }
-        }
 
-        const MCInstrDesc &UseDesc = UseMI->getDesc();
 
-        // Don't fold into target independent nodes.  Target independent opcodes
-        // don't have defined register classes.
-        if (UseDesc.isVariadic() ||
-            UseDesc.OpInfo[Use.getOperandNo()].RegClass == -1)
-          continue;
+      UseDesc.OpInfo[UseOpIdx].RegClass == -1)
+    return;
 
-        if (FoldingImm) {
-          MachineOperand ImmOp = MachineOperand::CreateImm(Imm.getSExtValue());
-          tryAddToFoldList(FoldList, UseMI, Use.getOperandNo(), &ImmOp, TII);
-          continue;
-        }
+    tryAddToFoldList(FoldList, UseMI, UseOpIdx, &ImmOp, TII);
+    return;
 
-        tryAddToFoldList(FoldList, UseMI, Use.getOperandNo(), &OpToFold, TII);
+  tryAddToFoldList(FoldList, UseMI, UseOpIdx, &OpToFold, TII);
 
-        // FIXME: We could try to change the instruction from 64-bit to 32-bit
-        // to enable more folding opportunites.  The shrink operands pass
-        // already does this.
+  return;
+}
+
+bool SIFoldOperands::runOnMachineFunction(MachineFunction &MF) {
+  MachineRegisterInfo &MRI = MF.getRegInfo();
+  const SIInstrInfo *TII =
+      static_cast<const SIInstrInfo *>(MF.getSubtarget().getInstrInfo());
+  const SIRegisterInfo &TRI = TII->getRegisterInfo();
+
+  for (MachineFunction::iterator BI = MF.begin(), BE = MF.end();
+                                                  BI != BE; ++BI) {
+
+    MachineBasicBlock &MBB = *BI;
+    MachineBasicBlock::iterator I, Next;
+    for (I = MBB.begin(); I != MBB.end(); I = Next) {
+      Next = std::next(I);
+      MachineInstr &MI = *I;
+
+      if (!isSafeToFold(MI.getOpcode()))
+        continue;
+
+      unsigned OpSize = TII->getOpSize(MI, 1);
+      MachineOperand &OpToFold = MI.getOperand(1);
+      bool FoldingImm = OpToFold.isImm();
+
+      // FIXME: We could also be folding things like FrameIndexes and
+      // TargetIndexes.
+      if (!FoldingImm && !OpToFold.isReg())
+        continue;
+
+      // Folding immediates with more than one use will increase program size.
+      // FIXME: This will also reduce register usage, which may be better
+      // in some cases.  A better heuristic is needed.
+      if (FoldingImm && !TII->isInlineConstant(OpToFold, OpSize) &&
+          !MRI.hasOneUse(MI.getOperand(0).getReg()))
+        continue;
+
+      // FIXME: Fold operands with subregs.
+      if (OpToFold.isReg() &&
+          (!TargetRegisterInfo::isVirtualRegister(OpToFold.getReg()) ||
+           OpToFold.getSubReg()))
+        continue;
+
+      std::vector<FoldCandidate> FoldList;
+      for (MachineRegisterInfo::use_iterator
+           Use = MRI.use_begin(MI.getOperand(0).getReg()), E = MRI.use_end();
+           Use != E; ++Use) {
+
+        MachineInstr *UseMI = Use->getParent();
+
+        foldOperand(OpToFold, UseMI, Use.getOperandNo(), FoldList,
+                    TII, TRI, MRI);
       }
 
       for (FoldCandidate &Fold : FoldList) {
         if (updateOperand(Fold, TRI)) {
           // Clear kill flags.
           if (!Fold.isImm()) {
             assert(Fold.OpToFold && Fold.OpToFold->isReg());
             Fold.OpToFold->setIsKill(false);