[ARM] Remove always-true checks from Thumb1 frame lowering (NFC) (#110283)

For Thumb1, we always split the callee-saved register pushes at R7, so
we don't need to check for this.

Author: ostannard

llvm/lib/Target/ARM/Thumb1FrameLowering.cpp

@@ -160,8 +160,8 @@ void Thumb1FrameLowering::emitPrologue(MachineFunction &MF,
   assert(NumBytes >= ArgRegsSaveSize &&
          "ArgRegsSaveSize is included in NumBytes");
   const std::vector<CalleeSavedInfo> &CSI = MFI.getCalleeSavedInfo();
-  ARMSubtarget::PushPopSplitVariation PushPopSplit =
-      STI.getPushPopSplitVariation(MF);
+  assert(STI.getPushPopSplitVariation(MF) == ARMSubtarget::SplitR7 &&
+         "Must use R7 spilt for Thumb1");
 
   // Debug location must be unknown since the first debug location is used
   // to determine the end of the prologue.
@@ -223,11 +223,8 @@ void Thumb1FrameLowering::emitPrologue(MachineFunction &MF,
     case ARM::R8:
     case ARM::R9:
     case ARM::R10:
-      if (PushPopSplit == ARMSubtarget::SplitR7) {
-        GPRCS2Size += 4;
-        break;
-      }
-      [[fallthrough]];
+      GPRCS2Size += 4;
+      break;
     case ARM::LR:
       if (HasFrameRecordArea) {
         FRSize += 4;
@@ -367,9 +364,7 @@ void Thumb1FrameLowering::emitPrologue(MachineFunction &MF,
       case ARM::R10:
       case ARM::R11:
       case ARM::R12:
-        if (PushPopSplit == ARMSubtarget::SplitR7)
-          break;
-        [[fallthrough]];
+        break;
       case ARM::R0:
       case ARM::R1:
       case ARM::R2: