[RISCV] Simplify tracking of tracking and encoding of push/pop in RISCVFrameLowering. NFC (#129343)

Previously we calculated the max register id. Then converted it to the number
of registers and encoding. Then converted number of registers to stack
size. Then saved number of registers, encoding, and stack size to
MachineFunctionInfo.

This patch removes the calculation of max register id, and instead
calculates the number of registers. The encoding is removed from
MachineFunctionInfo in favor of converting the number of registers to
encoding at the time of use.

Author: topperc

llvm/lib/Target/RISCV/MCTargetDesc/RISCVBaseInfo.h

@@ -624,6 +624,15 @@ inline unsigned encodeRlist(MCRegister EndReg, bool IsRV32E = false) {
   }
 }
 
+inline static unsigned encodeRlistNumRegs(unsigned NumRegs) {
+  assert(NumRegs > 0 && NumRegs < 14 && NumRegs != 12 &&
+         "Unexpected number of registers");
+  if (NumRegs == 13)
+    return RLISTENCODE::RA_S0_S11;
+
+  return RLISTENCODE::RA + (NumRegs - 1);
+}
+
 inline static unsigned getStackAdjBase(unsigned RlistVal, bool IsRV64) {
   assert(RlistVal != RLISTENCODE::INVALID_RLIST &&
          "{ra, s0-s10} is not supported, s11 must be included.");

llvm/lib/Target/RISCV/RISCVFrameLowering.cpp

@@ -332,51 +332,19 @@ getRestoreLibCallName(const MachineFunction &MF,
   return RestoreLibCalls[LibCallID];
 }
 
-// Return encoded value and register count for PUSH/POP instruction,
-// representing registers to store/load.
-static std::pair<unsigned, unsigned>
-getPushPopEncodingAndNum(const Register MaxReg) {
-  switch (MaxReg.id()) {
-  default:
-    llvm_unreachable("Unexpected Reg for Push/Pop Inst");
-  case RISCV::X27: /*s11*/
-    return std::make_pair(llvm::RISCVZC::RLISTENCODE::RA_S0_S11, 13);
-  case RISCV::X25: /*s9*/
-    return std::make_pair(llvm::RISCVZC::RLISTENCODE::RA_S0_S9, 11);
-  case RISCV::X24: /*s8*/
-    return std::make_pair(llvm::RISCVZC::RLISTENCODE::RA_S0_S8, 10);
-  case RISCV::X23: /*s7*/
-    return std::make_pair(llvm::RISCVZC::RLISTENCODE::RA_S0_S7, 9);
-  case RISCV::X22: /*s6*/
-    return std::make_pair(llvm::RISCVZC::RLISTENCODE::RA_S0_S6, 8);
-  case RISCV::X21: /*s5*/
-    return std::make_pair(llvm::RISCVZC::RLISTENCODE::RA_S0_S5, 7);
-  case RISCV::X20: /*s4*/
-    return std::make_pair(llvm::RISCVZC::RLISTENCODE::RA_S0_S4, 6);
-  case RISCV::X19: /*s3*/
-    return std::make_pair(llvm::RISCVZC::RLISTENCODE::RA_S0_S3, 5);
-  case RISCV::X18: /*s2*/
-    return std::make_pair(llvm::RISCVZC::RLISTENCODE::RA_S0_S2, 4);
-  case RISCV::X9: /*s1*/
-    return std::make_pair(llvm::RISCVZC::RLISTENCODE::RA_S0_S1, 3);
-  case FPReg: /*s0*/
-    return std::make_pair(llvm::RISCVZC::RLISTENCODE::RA_S0, 2);
-  case RAReg: /*ra*/
-    return std::make_pair(llvm::RISCVZC::RLISTENCODE::RA, 1);
-  }
-}
-
 // Get the max reg of Push/Pop for restoring callee saved registers.
-static Register getMaxPushPopReg(const std::vector<CalleeSavedInfo> &CSI) {
-  MCRegister MaxPushPopReg;
+static unsigned getNumPushPopRegs(const std::vector<CalleeSavedInfo> &CSI) {
+  unsigned NumPushPopRegs = 0;
   for (auto &CS : CSI) {
-    if (llvm::find_if(FixedCSRFIMap, [&](MCPhysReg P) {
-          return P == CS.getReg();
-        }) != std::end(FixedCSRFIMap))
-      MaxPushPopReg = std::max(MaxPushPopReg.id(), CS.getReg().id());
+    auto *FII = llvm::find_if(FixedCSRFIMap,
+                              [&](MCPhysReg P) { return P == CS.getReg(); });
+    if (FII != std::end(FixedCSRFIMap)) {
+      unsigned RegNum = std::distance(std::begin(FixedCSRFIMap), FII);
+      NumPushPopRegs = std::max(NumPushPopRegs, RegNum + 1);
+    }
   }
-  assert(MaxPushPopReg != RISCV::X26 && "x26 requires x27 to also be pushed");
-  return MaxPushPopReg;
+  assert(NumPushPopRegs != 12 && "x26 requires x27 to also be pushed");
+  return NumPushPopRegs;
 }
 
 // Return true if the specified function should have a dedicated frame
@@ -1790,14 +1758,10 @@ bool RISCVFrameLowering::assignCalleeSavedSpillSlots(
 
   if (RVFI->isPushable(MF)) {
     // Determine how many GPRs we need to push and save it to RVFI.
-    Register MaxReg = getMaxPushPopReg(CSI);
-    if (MaxReg != RISCV::NoRegister) {
-      auto [RegEnc, PushedRegNum] = getPushPopEncodingAndNum(MaxReg);
+    unsigned PushedRegNum = getNumPushPopRegs(CSI);
+    if (PushedRegNum) {
       RVFI->setRVPushRegs(PushedRegNum);
       RVFI->setRVPushStackSize(alignTo((STI.getXLen() / 8) * PushedRegNum, 16));
-
-      // Use encoded number to represent registers to spill.
-      RVFI->setRVPushRlist(RegEnc);
     }
   }
 
@@ -1881,11 +1845,11 @@ bool RISCVFrameLowering::spillCalleeSavedRegisters(
     unsigned PushedRegNum = RVFI->getRVPushRegs();
     if (PushedRegNum > 0) {
       // Use encoded number to represent registers to spill.
-      int RegEnc = RVFI->getRVPushRlist();
+      unsigned RegEnc = RISCVZC::encodeRlistNumRegs(PushedRegNum);
       MachineInstrBuilder PushBuilder =
           BuildMI(MBB, MI, DL, TII.get(RISCV::CM_PUSH))
               .setMIFlag(MachineInstr::FrameSetup);
-      PushBuilder.addImm((int64_t)RegEnc);
+      PushBuilder.addImm(RegEnc);
       PushBuilder.addImm(0);
 
       for (unsigned i = 0; i < PushedRegNum; i++)
@@ -2034,8 +1998,9 @@ bool RISCVFrameLowering::restoreCalleeSavedRegisters(
 
   RISCVMachineFunctionInfo *RVFI = MF->getInfo<RISCVMachineFunctionInfo>();
   if (RVFI->isPushable(*MF)) {
-    int RegEnc = RVFI->getRVPushRlist();
-    if (RegEnc != llvm::RISCVZC::RLISTENCODE::INVALID_RLIST) {
+    unsigned PushedRegNum = RVFI->getRVPushRegs();
+    if (PushedRegNum > 0) {
+      unsigned RegEnc = RISCVZC::encodeRlistNumRegs(PushedRegNum);
       MachineInstrBuilder PopBuilder =
           BuildMI(MBB, MI, DL, TII.get(RISCV::CM_POP))
               .setMIFlag(MachineInstr::FrameDestroy);

llvm/lib/Target/RISCV/RISCVMachineFunctionInfo.h

@@ -74,7 +74,6 @@ class RISCVMachineFunctionInfo : public MachineFunctionInfo {
   /// Size of stack frame for Zcmp PUSH/POP
   unsigned RVPushStackSize = 0;
   unsigned RVPushRegs = 0;
-  int RVPushRlist = llvm::RISCVZC::RLISTENCODE::INVALID_RLIST;
 
   int64_t StackProbeSize = 0;
 
@@ -146,9 +145,6 @@ class RISCVMachineFunctionInfo : public MachineFunctionInfo {
            VarArgsSaveSize == 0;
   }
 
-  int getRVPushRlist() const { return RVPushRlist; }
-  void setRVPushRlist(int Rlist) { RVPushRlist = Rlist; }
-
   unsigned getRVPushRegs() const { return RVPushRegs; }
   void setRVPushRegs(unsigned Regs) { RVPushRegs = Regs; }