[RISCV] Add X27 to SavedRegs when X26 is in SavedRegs for cm.push/pop (#92067)

cm.push can't save X26 without also saving X27. This removes two other
checks for this case.

This causes CFI to be emitted since X27 is now explicitly a callee saved
register.

The affected tests use inline assembly to clobber X26 rather than the
whole range of s0-s10.

Author: topperc

llvm/lib/Target/RISCV/RISCVFrameLowering.cpp

@@ -265,7 +265,6 @@ getPushPopEncodingAndNum(const Register MaxReg) {
   default:
     llvm_unreachable("Unexpected Reg for Push/Pop Inst");
   case RISCV::X27: /*s11*/
-  case RISCV::X26: /*s10*/
     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);
@@ -302,9 +301,7 @@ static Register getMaxPushPopReg(const MachineFunction &MF,
         }) != std::end(FixedCSRFIMap))
       MaxPushPopReg = std::max(MaxPushPopReg.id(), CS.getReg().id());
   }
-  // if rlist is {rs, s0-s10}, then s11 will also be included
-  if (MaxPushPopReg == RISCV::X26)
-    MaxPushPopReg = RISCV::X27;
+  assert(MaxPushPopReg != RISCV::X26 && "x26 requires x27 to also be pushed");
   return MaxPushPopReg;
 }
 
@@ -1047,6 +1044,11 @@ void RISCVFrameLowering::determineCalleeSaves(MachineFunction &MF,
   // Mark BP as used if function has dedicated base pointer.
   if (hasBP(MF))
     SavedRegs.set(RISCVABI::getBPReg());
+
+  // When using cm.push/pop we must save X27 if we save X26.
+  auto *RVFI = MF.getInfo<RISCVMachineFunctionInfo>();
+  if (RVFI->isPushable(MF) && SavedRegs.test(RISCV::X26))
+    SavedRegs.set(RISCV::X27);
 }
 
 std::pair<int64_t, Align>

llvm/test/CodeGen/RISCV/push-pop-popret.ll

@@ -3225,6 +3225,7 @@ define void @spill_x10() {
 ; RV32IZCMP-NEXT:    cm.push {ra, s0-s11}, -64
 ; RV32IZCMP-NEXT:    .cfi_def_cfa_offset 64
 ; RV32IZCMP-NEXT:    .cfi_offset s10, -8
+; RV32IZCMP-NEXT:    .cfi_offset s11, -4
 ; RV32IZCMP-NEXT:    #APP
 ; RV32IZCMP-NEXT:    li s10, 0
 ; RV32IZCMP-NEXT:    #NO_APP
@@ -3235,6 +3236,7 @@ define void @spill_x10() {
 ; RV64IZCMP-NEXT:    cm.push {ra, s0-s11}, -112
 ; RV64IZCMP-NEXT:    .cfi_def_cfa_offset 112
 ; RV64IZCMP-NEXT:    .cfi_offset s10, -16
+; RV64IZCMP-NEXT:    .cfi_offset s11, -8
 ; RV64IZCMP-NEXT:    #APP
 ; RV64IZCMP-NEXT:    li s10, 0
 ; RV64IZCMP-NEXT:    #NO_APP
@@ -3245,6 +3247,7 @@ define void @spill_x10() {
 ; RV32IZCMP-SR-NEXT:    cm.push {ra, s0-s11}, -64
 ; RV32IZCMP-SR-NEXT:    .cfi_def_cfa_offset 64
 ; RV32IZCMP-SR-NEXT:    .cfi_offset s10, -8
+; RV32IZCMP-SR-NEXT:    .cfi_offset s11, -4
 ; RV32IZCMP-SR-NEXT:    #APP
 ; RV32IZCMP-SR-NEXT:    li s10, 0
 ; RV32IZCMP-SR-NEXT:    #NO_APP
@@ -3255,6 +3258,7 @@ define void @spill_x10() {
 ; RV64IZCMP-SR-NEXT:    cm.push {ra, s0-s11}, -112
 ; RV64IZCMP-SR-NEXT:    .cfi_def_cfa_offset 112
 ; RV64IZCMP-SR-NEXT:    .cfi_offset s10, -16
+; RV64IZCMP-SR-NEXT:    .cfi_offset s11, -8
 ; RV64IZCMP-SR-NEXT:    #APP
 ; RV64IZCMP-SR-NEXT:    li s10, 0
 ; RV64IZCMP-SR-NEXT:    #NO_APP