[GISel][CombinerHelper] Add a function that chains a list of generators together

Author: ValentijnvdBeek

llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp

@@ -398,6 +398,21 @@ adderGenerator(const int32_t From, const int32_t To, const int32_t StepSize) {
   };
 }
 
+// Move to the next generator if it is exhausted allowing to chain generators
+std::function<std::optional<int32_t>()> concatGenerators(
+    SmallVector<std::function<std::optional<int32_t>()>> Generators) {
+  auto *GeneratorIterator = Generators.begin();
+
+  return [GeneratorIterator, Generators]() mutable {
+    std::optional<int32_t> GenValue = (*GeneratorIterator)();
+    if (!GenValue.has_value() && GeneratorIterator != Generators.end()) {
+      GeneratorIterator++;
+      GenValue = (*GeneratorIterator)();
+    }
+    return GenValue;
+  };
+}
+
 Register CombinerHelper::createUnmergeValue(
     MachineInstr &MI, const Register SrcReg, const Register DstReg,
     const uint8_t DestinationIndex, const uint32_t Start, const uint32_t End) {
@@ -419,31 +434,32 @@ Register CombinerHelper::createUnmergeValue(
     TargetReg = MRI.createGenericVirtualRegister(HalfSizeTy);
   }
 
-  // Each destination fits n times into the source and each iteration we exactly
-  // half the source. Therefore we need to pick on which side we want to iterate
-  // on.
-  const uint32_t DstNumElements = DstTy.isVector() ? DstTy.getNumElements() : 1;
-  const uint32_t HalfWay = Start + ((End - Start) / 2);
-  const uint32_t Position = DestinationIndex * DstNumElements;
-
-  uint32_t NextStart, NextEnd;
-  if (Position < HalfWay) {
-    Builder.buildInstr(TargetOpcode::G_UNMERGE_VALUES, {TargetReg, TmpReg},
-                       {SrcReg});
-    NextStart = Start;
-    NextEnd = HalfWay;
-  } else {
-    Builder.buildInstr(TargetOpcode::G_UNMERGE_VALUES, {TmpReg, TargetReg},
-                       {SrcReg});
-    NextStart = HalfWay;
-    NextEnd = End;
-  }
+    // Each destination fits n times into the source and each iteration we
+    // exactly half the source. Therefore we need to pick on which side we want
+    // to iterate on.
+    const uint32_t DstNumElements =
+        DstTy.isVector() ? DstTy.getNumElements() : 1;
+    const uint32_t HalfWay = Start + ((End - Start) / 2);
+    const uint32_t Position = DestinationIndex * DstNumElements;
+
+    uint32_t NextStart, NextEnd;
+    if (Position < HalfWay) {
+      Builder.buildInstr(TargetOpcode::G_UNMERGE_VALUES, {TargetReg, TmpReg},
+                         {SrcReg});
+      NextStart = Start;
+      NextEnd = HalfWay;
+    } else {
+      Builder.buildInstr(TargetOpcode::G_UNMERGE_VALUES, {TmpReg, TargetReg},
+                         {SrcReg});
+      NextStart = HalfWay;
+      NextEnd = End;
+    }
 
-  if (HalfSizeTy.isVector() && DstTy != HalfSizeTy)
-    return createUnmergeValue(MI, TargetReg, DstReg, DestinationIndex,
-                              NextStart, NextEnd);
+    if (HalfSizeTy.isVector() && DstTy != HalfSizeTy)
+      return createUnmergeValue(MI, TargetReg, DstReg, DestinationIndex,
+                                NextStart, NextEnd);
 
-  return DstReg;
+    return DstReg;
 }
 
 bool CombinerHelper::tryCombineShuffleVector(MachineInstr &MI) {