[AMDGPU] add missing checks in processBaseWithConstOffset (llvm#102310)

fixes llvm#102231 by inserting
missing checks.

(cherry picked from commit 273e0a4)

Author: tgymnich

llvm/lib/Target/AMDGPU/SILoadStoreOptimizer.cpp

@@ -2041,6 +2041,9 @@ void SILoadStoreOptimizer::processBaseWithConstOffset(const MachineOperand &Base
     BaseLo = *Src0;
   }
 
+  if (!BaseLo.isReg())
+    return;
+
   Src0 = TII->getNamedOperand(*BaseHiDef, AMDGPU::OpName::src0);
   Src1 = TII->getNamedOperand(*BaseHiDef, AMDGPU::OpName::src1);
 
@@ -2053,6 +2056,9 @@ void SILoadStoreOptimizer::processBaseWithConstOffset(const MachineOperand &Base
   uint64_t Offset1 = Src1->getImm();
   BaseHi = *Src0;
 
+  if (!BaseHi.isReg())
+    return;
+
   Addr.Base.LoReg = BaseLo.getReg();
   Addr.Base.HiReg = BaseHi.getReg();
   Addr.Base.LoSubReg = BaseLo.getSubReg();