AMDGPU: Replace some uses of getOpRegClass with getRegClass (#167447)

These cases should not depend on an unknown register constraint.

Author: arsenm

llvm/lib/Target/AMDGPU/SIISelLowering.cpp

@@ -17367,12 +17367,14 @@ void SITargetLowering::AddMemOpInit(MachineInstr &MI) const {
     // Abandon attempt if the dst size isn't large enough
     // - this is in fact an error but this is picked up elsewhere and
     // reported correctly.
-    uint32_t DstSize =
-        TRI.getRegSizeInBits(*TII->getOpRegClass(MI, DstIdx)) / 32;
+    const TargetRegisterClass *DstRC = TII->getRegClass(MI.getDesc(), DstIdx);
+
+    uint32_t DstSize = TRI.getRegSizeInBits(*DstRC) / 32;
     if (DstSize < InitIdx)
       return;
   } else if (TII->isMUBUF(MI) && AMDGPU::getMUBUFTfe(MI.getOpcode())) {
-    InitIdx = TRI.getRegSizeInBits(*TII->getOpRegClass(MI, DstIdx)) / 32;
+    const TargetRegisterClass *DstRC = TII->getRegClass(MI.getDesc(), DstIdx);
+    InitIdx = TRI.getRegSizeInBits(*DstRC) / 32;
   } else {
     return;
   }

llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp

@@ -3046,7 +3046,7 @@ bool SIRegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator MI,
     if (!IsMUBUF && !MFI->isBottomOfStack()) {
       // Convert to a swizzled stack address by scaling by the wave size.
       // In an entry function/kernel the offset is already swizzled.
-      bool IsSALU = isSGPRClass(TII->getOpRegClass(*MI, FIOperandNum));
+      bool IsSALU = isSGPRClass(TII->getRegClass(MI->getDesc(), FIOperandNum));
       bool LiveSCC = RS->isRegUsed(AMDGPU::SCC) &&
                      !MI->definesRegister(AMDGPU::SCC, /*TRI=*/nullptr);
       const TargetRegisterClass *RC = IsSALU && !LiveSCC