[M68k][MIR](2/8) Changes in the target-independent MIR part

 - Add new callback in `TargetInstrInfo` --
  `isPCRelRegisterOperandLegal` -- to query whether pc-rel
   register MachineOperand is legal.
 - Add new function to search DebugLoc in a reverse ordering

Authors: myhsu, m4yers, glaubitz

Differential Revision: https://reviews.llvm.org/D88386

Author: mshockwave

llvm/include/llvm/CodeGen/MachineBasicBlock.h

@@ -895,13 +895,29 @@ class MachineBasicBlock
     return findDebugLoc(MBBI.getInstrIterator());
   }
 
+  /// Has exact same behavior as @ref findDebugLoc (it also
+  /// searches from the first to the last MI of this MBB) except
+  /// that this takes reverse iterator.
+  DebugLoc rfindDebugLoc(reverse_instr_iterator MBBI);
+  DebugLoc rfindDebugLoc(reverse_iterator MBBI) {
+    return rfindDebugLoc(MBBI.getInstrIterator());
+  }
+
   /// Find the previous valid DebugLoc preceding MBBI, skipping and DBG_VALUE
   /// instructions.  Return UnknownLoc if there is none.
   DebugLoc findPrevDebugLoc(instr_iterator MBBI);
   DebugLoc findPrevDebugLoc(iterator MBBI) {
     return findPrevDebugLoc(MBBI.getInstrIterator());
   }
 
+  /// Has exact same behavior as @ref findPrevDebugLoc (it also
+  /// searches from the last to the first MI of this MBB) except
+  /// that this takes reverse iterator.
+  DebugLoc rfindPrevDebugLoc(reverse_instr_iterator MBBI);
+  DebugLoc rfindPrevDebugLoc(reverse_iterator MBBI) {
+    return rfindPrevDebugLoc(MBBI.getInstrIterator());
+  }
+
   /// Find and return the merged DebugLoc of the branch instructions of the
   /// block. Return UnknownLoc if there is none.
   DebugLoc findBranchDebugLoc();

llvm/include/llvm/CodeGen/TargetInstrInfo.h

@@ -951,6 +951,19 @@ class TargetInstrInfo : public MCInstrInfo {
     llvm_unreachable("Target didn't implement TargetInstrInfo::copyPhysReg!");
   }
 
+  /// Allow targets to tell MachineVerifier whether a specific register
+  /// MachineOperand can be used as part of PC-relative addressing.
+  /// PC-relative addressing modes in many CISC architectures contain
+  /// (non-PC) registers as offsets or scaling values, which inherently
+  /// tags the corresponding MachineOperand with OPERAND_PCREL.
+  ///
+  /// @param MO The MachineOperand in question. MO.isReg() should always
+  /// be true.
+  /// @return Whether this operand is allowed to be used PC-relatively.
+  virtual bool isPCRelRegisterOperandLegal(const MachineOperand &MO) const {
+    return false;
+  }
+
 protected:
   /// Target-dependent implementation for IsCopyInstr.
   /// If the specific machine instruction is a instruction that moves/copies

llvm/lib/CodeGen/MachineBasicBlock.cpp

@@ -1401,6 +1401,14 @@ MachineBasicBlock::findDebugLoc(instr_iterator MBBI) {
   return {};
 }
 
+DebugLoc MachineBasicBlock::rfindDebugLoc(reverse_instr_iterator MBBI) {
+  // Skip debug declarations, we don't want a DebugLoc from them.
+  MBBI = skipDebugInstructionsBackward(MBBI, instr_rbegin());
+  if (!MBBI->isDebugInstr())
+    return MBBI->getDebugLoc();
+  return {};
+}
+
 /// Find the previous valid DebugLoc preceding MBBI, skipping and DBG_VALUE
 /// instructions.  Return UnknownLoc if there is none.
 DebugLoc MachineBasicBlock::findPrevDebugLoc(instr_iterator MBBI) {
@@ -1411,6 +1419,16 @@ DebugLoc MachineBasicBlock::findPrevDebugLoc(instr_iterator MBBI) {
   return {};
 }
 
+DebugLoc MachineBasicBlock::rfindPrevDebugLoc(reverse_instr_iterator MBBI) {
+  if (MBBI == instr_rend())
+    return {};
+  // Skip debug declarations, we don't want a DebugLoc from them.
+  MBBI = next_nodbg(MBBI, instr_rend());
+  if (MBBI != instr_rend())
+    return MBBI->getDebugLoc();
+  return {};
+}
+
 /// Find and return the merged DebugLoc of the branch instructions of the block.
 /// Return UnknownLoc if there is none.
 DebugLoc

llvm/lib/CodeGen/MachineVerifier.cpp

@@ -1762,9 +1762,12 @@ MachineVerifier::visitMachineOperand(const MachineOperand *MO, unsigned MONum) {
       if (MCOI.OperandType == MCOI::OPERAND_REGISTER &&
           !MO->isReg() && !MO->isFI())
         report("Expected a register operand.", MO, MONum);
-      if ((MCOI.OperandType == MCOI::OPERAND_IMMEDIATE ||
-           MCOI.OperandType == MCOI::OPERAND_PCREL) && MO->isReg())
-        report("Expected a non-register operand.", MO, MONum);
+      if (MO->isReg()) {
+        if (MCOI.OperandType == MCOI::OPERAND_IMMEDIATE ||
+            (MCOI.OperandType == MCOI::OPERAND_PCREL &&
+             !TII->isPCRelRegisterOperandLegal(*MO)))
+          report("Expected a non-register operand.", MO, MONum);
+      }
     }
 
     int TiedTo = MCID.getOperandConstraint(MONum, MCOI::TIED_TO);