[NFC][AArch64] Handle processLogicalImmediate error

[asavonic]

Summary

If processLogicalImmediate fails, we should return from the function
without changing InsInstrs or DelInstrs. This happens for
CodeGen/AArch64/urem-seteq-nonzero.ll LIT test as described in
https://reviews.llvm.org/D99662#2662296.

Callers of genAlternativeCodeSequence skip patterns where InsInstrs
stays empty, so this does not cause any issues now.

[asavonic]

This does not cause any issues now, because callers of genAlternativeCodeSequence skip patterns where InsInstrs is empty.
So the patch can be considered NFC.

[dmgreen]

Sounds OK

llvm/lib/Target/AArch64/AArch64InstrInfo.cpp

case MachineCombinerPattern::MULADDXI_OP1: {
     uint64_t Imm = Root.getOperand(2).getImm();
 
     if (Root.getOperand(3).isImm()) {
       unsigned Val = Root.getOperand(3).getImm();
       Imm = Imm << Val;
     }
     uint64_t UImm = SignExtend64(Imm, BitSize);
     uint64_t Encoding;
-    if (AArch64_AM::processLogicalImmediate(UImm, BitSize, Encoding)) {
-      MachineInstrBuilder MIB1 =
-          BuildMI(MF, Root.getDebugLoc(), TII->get(OrrOpc), NewVR)
-              .addReg(ZeroReg)
-              .addImm(Encoding);
-      InsInstrs.push_back(MIB1);
-      InstrIdxForVirtReg.insert(std::make_pair(NewVR, 0));
-      MUL = genMaddR(MF, MRI, TII, Root, InsInstrs, 1, Opc, NewVR, RC);
-    }
+    if (!AArch64_AM::processLogicalImmediate(UImm, BitSize, Encoding))
+      return;
     break;
   }
   case MachineCombinerPattern::MULSUBW_OP1:
   case MachineCombinerPattern::MULSUBX_OP1: {
     // MUL I=A,B,0
     // SUB R,I, C
     // ==> SUB  V, 0, C
     // ==> MADD R,A,B,V // = -C + A*B
case MachineCombinerPattern::MULSUBXI_OP1: {
     Register NewVR = MRI.createVirtualRegister(OrrRC);
     uint64_t Imm = Root.getOperand(2).getImm();
     if (Root.getOperand(3).isImm()) {
       unsigned Val = Root.getOperand(3).getImm();
       Imm = Imm << Val;
     }
     uint64_t UImm = SignExtend64(-Imm, BitSize);
     uint64_t Encoding;
-    if (AArch64_AM::processLogicalImmediate(UImm, BitSize, Encoding)) {
-      MachineInstrBuilder MIB1 =
-          BuildMI(MF, Root.getDebugLoc(), TII->get(OrrOpc), NewVR)
-              .addReg(ZeroReg)
-              .addImm(Encoding);
-      InsInstrs.push_back(MIB1);
-      InstrIdxForVirtReg.insert(std::make_pair(NewVR, 0));
-      MUL = genMaddR(MF, MRI, TII, Root, InsInstrs, 1, Opc, NewVR, RC);
-    }
+    if (!AArch64_AM::processLogicalImmediate(UImm, BitSize, Encoding))
+      return;
     break;
   }
 
   case MachineCombinerPattern::MULADDv8i8_OP1:
     Opc = AArch64::MLAv8i8;
     RC = &AArch64::FPR64RegClass;
     MUL = genFusedMultiplyAcc(MF, MRI, TII, Root, InsInstrs, 1, Opc, RC);
     break;
case MachineCombinerPattern::FMULv8i16_indexed_OP2: {
     unsigned IdxDupOp =
         (Pattern == MachineCombinerPattern::FMULv8i16_indexed_OP1) ? 1 : 2;
     genIndexedMultiply(Root, InsInstrs, IdxDupOp, AArch64::FMULv8i16_indexed,
                        &AArch64::FPR128_loRegClass, MRI);
     break;
   }
   } // end switch (Pattern)
   // Record MUL and ADD/SUB for deletion
-  // FIXME: This assertion fails in CodeGen/AArch64/tailmerging_in_mbp.ll and
-  // CodeGen/AArch64/urem-seteq-nonzero.ll.
-  // assert(MUL && "MUL was never set");
   if (MUL)
     DelInstrs.push_back(MUL);
   DelInstrs.push_back(&Root);
 }
 
 /// Replace csincr-branch sequence by simple conditional branch
 ///
 /// Examples: