Revert "[AMDGPU] RA inserted scalar instructions can be at the BB top (llvm#72140)"

This reverts commit ce7fd49.

Change-Id: Iafb1f24fad78c477d3168a69cd8f9ccde6bc5038

Author: alex-t

llvm/include/llvm/CodeGen/MachineBasicBlock.h

@@ -846,10 +846,8 @@ class MachineBasicBlock
 
   /// Return the first instruction in MBB after I that is not a PHI, label or
   /// debug.  This is the correct point to insert copies at the beginning of a
-  /// basic block. \p Reg is the register being used by a spill or defined for a
-  /// restore/split during register allocation.
-  iterator SkipPHIsLabelsAndDebug(iterator I, Register Reg = Register(),
-                                  bool SkipPseudoOp = true);
+  /// basic block.
+  iterator SkipPHIsLabelsAndDebug(iterator I, bool SkipPseudoOp = true);
 
   /// Returns an iterator to the first terminator instruction of this basic
   /// block. If a terminator does not exist, it returns end().

llvm/include/llvm/CodeGen/TargetInstrInfo.h

@@ -2013,10 +2013,8 @@ class TargetInstrInfo : public MCInstrInfo {
 
   /// True if the instruction is bound to the top of its basic block and no
   /// other instructions shall be inserted before it. This can be implemented
-  /// to prevent register allocator to insert spills for \p Reg before such
-  /// instructions.
-  virtual bool isBasicBlockPrologue(const MachineInstr &MI,
-                                    Register Reg = Register()) const {
+  /// to prevent register allocator to insert spills before such instructions.
+  virtual bool isBasicBlockPrologue(const MachineInstr &MI) const {
     return false;
   }
 

llvm/lib/CodeGen/FixupStatepointCallerSaved.cpp

@@ -461,8 +461,7 @@ class StatepointState {
 
       if (EHPad && !RC.hasReload(Reg, RegToSlotIdx[Reg], EHPad)) {
         RC.recordReload(Reg, RegToSlotIdx[Reg], EHPad);
-        auto EHPadInsertPoint =
-            EHPad->SkipPHIsLabelsAndDebug(EHPad->begin(), Reg);
+        auto EHPadInsertPoint = EHPad->SkipPHIsLabelsAndDebug(EHPad->begin());
         insertReloadBefore(Reg, EHPadInsertPoint, EHPad);
         LLVM_DEBUG(dbgs() << "...also reload at EHPad "
                           << printMBBReference(*EHPad) << "\n");

llvm/lib/CodeGen/InlineSpiller.cpp

@@ -463,7 +463,7 @@ bool InlineSpiller::hoistSpillInsideBB(LiveInterval &SpillLI,
   MachineBasicBlock *MBB = LIS.getMBBFromIndex(SrcVNI->def);
   MachineBasicBlock::iterator MII;
   if (SrcVNI->isPHIDef())
-    MII = MBB->SkipPHIsLabelsAndDebug(MBB->begin(), SrcReg);
+    MII = MBB->SkipPHIsLabelsAndDebug(MBB->begin());
   else {
     MachineInstr *DefMI = LIS.getInstructionFromIndex(SrcVNI->def);
     assert(DefMI && "Defining instruction disappeared");

llvm/lib/CodeGen/MachineBasicBlock.cpp

@@ -223,13 +223,13 @@ MachineBasicBlock::SkipPHIsAndLabels(MachineBasicBlock::iterator I) {
 
 MachineBasicBlock::iterator
 MachineBasicBlock::SkipPHIsLabelsAndDebug(MachineBasicBlock::iterator I,
-                                          Register Reg, bool SkipPseudoOp) {
+                                          bool SkipPseudoOp) {
   const TargetInstrInfo *TII = getParent()->getSubtarget().getInstrInfo();
 
   iterator E = end();
   while (I != E && (I->isPHI() || I->isPosition() || I->isDebugInstr() ||
                     (SkipPseudoOp && I->isPseudoProbe()) ||
-                    TII->isBasicBlockPrologue(*I, Reg)))
+                    TII->isBasicBlockPrologue(*I)))
     ++I;
   // FIXME: This needs to change if we wish to bundle labels / dbg_values
   // inside the bundle.

llvm/lib/CodeGen/SplitKit.cpp

@@ -807,10 +807,8 @@ SlotIndex SplitEditor::leaveIntvAtTop(MachineBasicBlock &MBB) {
     return Start;
   }
 
-  unsigned RegIdx = 0;
-  Register Reg = LIS.getInterval(Edit->get(RegIdx)).reg();
-  VNInfo *VNI = defFromParent(RegIdx, ParentVNI, Start, MBB,
-                              MBB.SkipPHIsLabelsAndDebug(MBB.begin(), Reg));
+  VNInfo *VNI = defFromParent(0, ParentVNI, Start, MBB,
+                              MBB.SkipPHIsLabelsAndDebug(MBB.begin()));
   RegAssign.insert(Start, VNI->def, OpenIdx);
   LLVM_DEBUG(dump());
   return VNI->def;

llvm/lib/Target/AMDGPU/SIInstrInfo.cpp

@@ -8918,25 +8918,16 @@ unsigned SIInstrInfo::getLiveRangeSplitOpcode(Register SrcReg,
   return AMDGPU::COPY;
 }
 
-bool SIInstrInfo::isBasicBlockPrologue(const MachineInstr &MI,
-                                       Register Reg) const {
+bool SIInstrInfo::isBasicBlockPrologue(const MachineInstr &MI) const {
   // We need to handle instructions which may be inserted during register
   // allocation to handle the prolog. The initial prolog instruction may have
   // been separated from the start of the block by spills and copies inserted
-  // needed by the prolog. However, the insertions for scalar registers can
-  // always be placed at the BB top as they are independent of the exec mask
-  // value.
-  bool IsNullOrVectorRegister = true;
-  if (Reg) {
-    const MachineRegisterInfo &MRI = MI.getParent()->getParent()->getRegInfo();
-    IsNullOrVectorRegister = !RI.isSGPRClass(RI.getRegClassForReg(MRI, Reg));
-  }
-
+  // needed by the prolog.
   uint16_t Opc = MI.getOpcode();
+
   // FIXME: Copies inserted in the block prolog for live-range split should also
   // be included.
-  return IsNullOrVectorRegister &&
-         (isSpillOpcode(Opc) || (!MI.isTerminator() && Opc != AMDGPU::COPY &&
+  return (isSpillOpcode(Opc) || (!MI.isTerminator() && Opc != AMDGPU::COPY &&
                                  MI.modifiesRegister(AMDGPU::EXEC, &RI)));
 }
 

llvm/lib/Target/AMDGPU/SIInstrInfo.h

@@ -1283,8 +1283,7 @@ class SIInstrInfo final : public AMDGPUGenInstrInfo {
   unsigned getLiveRangeSplitOpcode(Register Reg,
                                    const MachineFunction &MF) const override;
 
-  bool isBasicBlockPrologue(const MachineInstr &MI,
-                            Register Reg = Register()) const override;
+  bool isBasicBlockPrologue(const MachineInstr &MI) const override;
 
   MachineInstr *createPHIDestinationCopy(MachineBasicBlock &MBB,
                                          MachineBasicBlock::iterator InsPt,