[X86] Move findDeadCallerSavedReg() into X86RegisterInfo

The findDeadCallerSavedReg() function has utility outside of X86FrameLowering.cpp

Differential Revision: https://reviews.llvm.org/D88924

llvm/lib/Target/X86/X86FrameLowering.cpp

@@ -148,60 +148,6 @@ static unsigned getLEArOpcode(bool IsLP64) {
   return IsLP64 ? X86::LEA64r : X86::LEA32r;
 }
 
-/// findDeadCallerSavedReg - Return a caller-saved register that isn't live
-/// when it reaches the "return" instruction. We can then pop a stack object
-/// to this register without worry about clobbering it.
-static unsigned findDeadCallerSavedReg(MachineBasicBlock &MBB,
-                                       MachineBasicBlock::iterator &MBBI,
-                                       const X86RegisterInfo *TRI,
-                                       bool Is64Bit) {
-  const MachineFunction *MF = MBB.getParent();
-  if (MF->callsEHReturn())
-    return 0;
-
-  const TargetRegisterClass &AvailableRegs = *TRI->getGPRsForTailCall(*MF);
-
-  if (MBBI == MBB.end())
-    return 0;
-
-  switch (MBBI->getOpcode()) {
-  default: return 0;
-  case TargetOpcode::PATCHABLE_RET:
-  case X86::RET:
-  case X86::RETL:
-  case X86::RETQ:
-  case X86::RETIL:
-  case X86::RETIQ:
-  case X86::TCRETURNdi:
-  case X86::TCRETURNri:
-  case X86::TCRETURNmi:
-  case X86::TCRETURNdi64:
-  case X86::TCRETURNri64:
-  case X86::TCRETURNmi64:
-  case X86::EH_RETURN:
-  case X86::EH_RETURN64: {
-    SmallSet<uint16_t, 8> Uses;
-    for (unsigned i = 0, e = MBBI->getNumOperands(); i != e; ++i) {
-      MachineOperand &MO = MBBI->getOperand(i);
-      if (!MO.isReg() || MO.isDef())
-        continue;
-      Register Reg = MO.getReg();
-      if (!Reg)
-        continue;
-      for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI)
-        Uses.insert(*AI);
-    }
-
-    for (auto CS : AvailableRegs)
-      if (!Uses.count(CS) && CS != X86::RIP && CS != X86::RSP &&
-          CS != X86::ESP)
-        return CS;
-  }
-  }
-
-  return 0;
-}
-
 static bool isEAXLiveIn(MachineBasicBlock &MBB) {
   for (MachineBasicBlock::RegisterMaskPair RegMask : MBB.liveins()) {
     unsigned Reg = RegMask.PhysReg;
@@ -288,7 +234,7 @@ void X86FrameLowering::emitSPUpdate(MachineBasicBlock &MBB,
     if (isSub && !isEAXLiveIn(MBB))
       Reg = Rax;
     else
-      Reg = findDeadCallerSavedReg(MBB, MBBI, TRI, Is64Bit);
+      Reg = TRI->findDeadCallerSavedReg(MBB, MBBI);
 
     unsigned MovRIOpc = Is64Bit ? X86::MOV64ri : X86::MOV32ri;
     unsigned AddSubRROpc =
@@ -345,7 +291,7 @@ void X86FrameLowering::emitSPUpdate(MachineBasicBlock &MBB,
       // need to find a dead register when using pop.
       unsigned Reg = isSub
         ? (unsigned)(Is64Bit ? X86::RAX : X86::EAX)
-        : findDeadCallerSavedReg(MBB, MBBI, TRI, Is64Bit);
+        : TRI->findDeadCallerSavedReg(MBB, MBBI);
       if (Reg) {
         unsigned Opc = isSub
           ? (Is64Bit ? X86::PUSH64r : X86::PUSH32r)

llvm/lib/Target/X86/X86RegisterInfo.cpp

@@ -18,6 +18,7 @@
 #include "X86Subtarget.h"
 #include "llvm/ADT/BitVector.h"
 #include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SmallSet.h"
 #include "llvm/CodeGen/MachineFrameInfo.h"
 #include "llvm/CodeGen/MachineFunction.h"
 #include "llvm/CodeGen/MachineFunctionPass.h"
@@ -790,6 +791,55 @@ X86RegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator II,
   }
 }
 
+unsigned X86RegisterInfo::findDeadCallerSavedReg(
+    MachineBasicBlock &MBB, MachineBasicBlock::iterator &MBBI) const {
+  const MachineFunction *MF = MBB.getParent();
+  if (MF->callsEHReturn())
+    return 0;
+
+  const TargetRegisterClass &AvailableRegs = *getGPRsForTailCall(*MF);
+
+  if (MBBI == MBB.end())
+    return 0;
+
+  switch (MBBI->getOpcode()) {
+  default:
+    return 0;
+  case TargetOpcode::PATCHABLE_RET:
+  case X86::RET:
+  case X86::RETL:
+  case X86::RETQ:
+  case X86::RETIL:
+  case X86::RETIQ:
+  case X86::TCRETURNdi:
+  case X86::TCRETURNri:
+  case X86::TCRETURNmi:
+  case X86::TCRETURNdi64:
+  case X86::TCRETURNri64:
+  case X86::TCRETURNmi64:
+  case X86::EH_RETURN:
+  case X86::EH_RETURN64: {
+    SmallSet<uint16_t, 8> Uses;
+    for (unsigned I = 0, E = MBBI->getNumOperands(); I != E; ++I) {
+      MachineOperand &MO = MBBI->getOperand(I);
+      if (!MO.isReg() || MO.isDef())
+        continue;
+      Register Reg = MO.getReg();
+      if (!Reg)
+        continue;
+      for (MCRegAliasIterator AI(Reg, this, true); AI.isValid(); ++AI)
+        Uses.insert(*AI);
+    }
+
+    for (auto CS : AvailableRegs)
+      if (!Uses.count(CS) && CS != X86::RIP && CS != X86::RSP && CS != X86::ESP)
+        return CS;
+  }
+  }
+
+  return 0;
+}
+
 Register X86RegisterInfo::getFrameRegister(const MachineFunction &MF) const {
   const X86FrameLowering *TFI = getFrameLowering(MF);
   return TFI->hasFP(MF) ? FramePtr : StackPtr;

llvm/lib/Target/X86/X86RegisterInfo.h

@@ -128,6 +128,12 @@ public:
                            int SPAdj, unsigned FIOperandNum,
                            RegScavenger *RS = nullptr) const override;
 
+  /// findDeadCallerSavedReg - Return a caller-saved register that isn't live
+  /// when it reaches the "return" instruction. We can then pop a stack object
+  /// to this register without worry about clobbering it.
+  unsigned findDeadCallerSavedReg(MachineBasicBlock &MBB,
+                                  MachineBasicBlock::iterator &MBBI) const;
+
   // Debug information queries.
   Register getFrameRegister(const MachineFunction &MF) const override;
   unsigned getPtrSizedFrameRegister(const MachineFunction &MF) const;