[PowerPC] Fix saving of Link Register when using ROP Protect (#123101)

An optimization was added that tries to move the uses of the mflr
instruction away from the instruction itself. However, this doesn't work
when we are using the hashst instruction because that instruction needs
to be run before the stack frame is obtained.

This patch disables moving instructions away from the mflr in the case
where ROP protection is being used.

---------

Co-authored-by: Lei Huang <[email protected]>

Author: stefanp-synopsys

llvm/lib/Target/PowerPC/PPCFrameLowering.cpp

@@ -646,7 +646,7 @@ void PPCFrameLowering::emitPrologue(MachineFunction &MF,
   bool HasFP = hasFP(MF);
   bool HasBP = RegInfo->hasBasePointer(MF);
   bool HasRedZone = isPPC64 || !isSVR4ABI;
-  bool HasROPProtect = Subtarget.hasROPProtect();
+  const bool HasROPProtect = Subtarget.hasROPProtect();
   bool HasPrivileged = Subtarget.hasPrivileged();
 
   Register SPReg       = isPPC64 ? PPC::X1  : PPC::R1;
@@ -908,8 +908,10 @@ void PPCFrameLowering::emitPrologue(MachineFunction &MF,
   // in ScratchReg.
   // If the offset can not be encoded into the store instruction, we also have
   // to save LR here.
+  // If we are using ROP Protection we need to save the LR here as we cannot
+  // move the hashst instruction past the point where we get the stack frame.
   if (MustSaveLR && !HasFastMFLR &&
-      (HasSTUX || !isInt<16>(FrameSize + LROffset)))
+      (HasSTUX || !isInt<16>(FrameSize + LROffset) || HasROPProtect))
     SaveLR(LROffset);
 
   // If FrameSize <= TLI.getStackProbeSize(MF), as POWER ABI requires backchain
@@ -1100,7 +1102,8 @@ void PPCFrameLowering::emitPrologue(MachineFunction &MF,
   }
 
   // Save the LR now.
-  if (!HasSTUX && MustSaveLR && !HasFastMFLR && isInt<16>(FrameSize + LROffset))
+  if (!HasSTUX && MustSaveLR && !HasFastMFLR &&
+      isInt<16>(FrameSize + LROffset) && !HasROPProtect)
     SaveLR(LROffset + FrameSize);
 
   // Add Call Frame Information for the instructions we generated above.