[RISCV] Simplify tracking of tracking and encoding of push/pop in RISCVFrameLowering. NFC

[topperc]

Previously we calculated the max register id. Then converted it 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.

[llvmbot]

@llvm/pr-subscribers-backend-risc-v

Author: Craig Topper (topperc)

Changes

Previously we calculated the max register id. Then converted it 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.

---

Full diff: https://github.com/llvm/llvm-project/pull/129343.diff

3 Files Affected:

• (modified) llvm/lib/Target/RISCV/MCTargetDesc/RISCVBaseInfo.h (+9)
• (modified) llvm/lib/Target/RISCV/RISCVFrameLowering.cpp (+17-52)
• (modified) llvm/lib/Target/RISCV/RISCVMachineFunctionInfo.h (-4)

diff --git a/llvm/lib/Target/RISCV/MCTargetDesc/RISCVBaseInfo.h b/llvm/lib/Target/RISCV/MCTargetDesc/RISCVBaseInfo.h
index 185a5d8a9c9b2..d82ec0cb07a54 100644
--- a/llvm/lib/Target/RISCV/MCTargetDesc/RISCVBaseInfo.h
+++ b/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)
+    --NumRegs;
+
+  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.");
diff --git a/llvm/lib/Target/RISCV/RISCVFrameLowering.cpp b/llvm/lib/Target/RISCV/RISCVFrameLowering.cpp
index 8a18e681e1b85..bcc1909a5d195 100644
--- a/llvm/lib/Target/RISCV/RISCVFrameLowering.cpp
+++ b/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, [&](auto P) {
-          return P.first == CS.getReg();
-        }) != std::end(FixedCSRFIMap))
-      MaxPushPopReg = std::max(MaxPushPopReg.id(), CS.getReg().id());
+    auto *FII = llvm::find_if(FixedCSRFIMap,
+                              [&](auto P) { return P.first == 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);
     }
   }
 
@@ -1879,11 +1843,11 @@ 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++)
@@ -2032,8 +1996,9 @@ 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);
diff --git a/llvm/lib/Target/RISCV/RISCVMachineFunctionInfo.h b/llvm/lib/Target/RISCV/RISCVMachineFunctionInfo.h
index 27a13bb7cace1..3f88439086e56 100644
--- a/llvm/lib/Target/RISCV/RISCVMachineFunctionInfo.h
+++ b/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; }
 

[lenary]

LGTM. Two small nits

I don't really like the variable name "PushedRegNum" used in a few places - it reads to me as "Pushed Register Number" (something singular), rather than "Number of Pushed Registers" (something more obviously pushing multiple). I can do that tidy-up later though.