[Z80] Avoid redundant boolean materialization in branch conditions

Author: Sightem

llvm/lib/Target/Z80/GISel/Z80InstructionSelector.cpp

@@ -2717,8 +2717,17 @@ Z80InstructionSelector::foldSetCC(MachineInstr &I, MachineIRBuilder &MIB,
   for (MachineBasicBlock::iterator II = I, EI = MIB.getInsertPt(); II != EI; ++II) {
     if (II == MBB.end())
       return Z80::COND_INVALID;
+
+    if (II->isDebugInstr())
+      continue;
+
+    if (II->modifiesRegister(Z80::F, &TRI))
+      return Z80::COND_INVALID;
+    
     switch (II->getOpcode()) {
     case Z80::SetCC:
+    case TargetOpcode::COPY:
+    case TargetOpcode::G_TRUNC:
       continue;
     }
     return Z80::COND_INVALID;

llvm/lib/Target/Z80/Z80Combine.td

@@ -66,6 +66,6 @@ def Z80PreLegalizerCombiner
 
 def Z80PostLegalizerCombiner
     : GICombiner<"Z80PostLegalizerCombinerImpl", [
-        combine_identity, narrow_op, simplify_known_const, trunc_ext_fold,
-        unmerge_zext_to_zext,
+        combine_identity, narrow_op, select_same_val, simplify_known_const,
+        trunc_ext_fold, unmerge_zext_to_zext,
     ]>;