[aarch64][globalisel] Fix a crash in selectAddrModeIndexed() caused by incorrect G_FRAME_INDEX handling

The wrong operand was being rendered to the result instruction.

The crash was detected by Bitcode/simd_ops/AArch64_halide_runtime.bc

llvm-svn: 315890
diff --git a/llvm/lib/Target/AArch64/AArch64InstructionSelector.cpp b/llvm/lib/Target/AArch64/AArch64InstructionSelector.cpp
index 622bf99..9fb005b 100644
--- a/llvm/lib/Target/AArch64/AArch64InstructionSelector.cpp
+++ b/llvm/lib/Target/AArch64/AArch64InstructionSelector.cpp
@@ -1497,7 +1497,11 @@
       unsigned Scale = Log2_32(Size);
       if ((RHSC & (Size - 1)) == 0 && RHSC >= 0 && RHSC < (0x1000 << Scale)) {
         if (LHSDef->getOpcode() == TargetOpcode::G_FRAME_INDEX)
-          LHSDef = MRI.getVRegDef(LHSDef->getOperand(1).getReg());
+          return {{
+              [=](MachineInstrBuilder &MIB) { MIB.add(LHSDef->getOperand(1)); },
+              [=](MachineInstrBuilder &MIB) { MIB.addImm(RHSC >> Scale); },
+          }};
+
         return {{
             [=](MachineInstrBuilder &MIB) { MIB.add(LHS); },
             [=](MachineInstrBuilder &MIB) { MIB.addImm(RHSC >> Scale); },