[GISel][CombinerHelper] Add a generator that counts from 0 to n

Author: ValentijnvdBeek

llvm/include/llvm/CodeGen/GlobalISel/CombinerHelper.h

@@ -27,6 +27,7 @@
 #include "llvm/CodeGenTypes/LowLevelType.h"
 #include "llvm/IR/InstrTypes.h"
 #include <functional>
+#include <optional>
 
 namespace llvm {
 
@@ -246,6 +247,12 @@ class CombinerHelper {
   void applyCombineShuffleConcat(MachineInstr &MI, SmallVector<Register> &Ops);
 
   /// Try to combine G_SHUFFLE_VECTOR into G_CONCAT_VECTORS.
+  /// A function type that returns either the next value in a
+  /// shufflemask or an empty value. Each iteration should return
+  /// one value, like a Python iterator or a Lisp stream.
+  using GeneratorType = std::function<std::optional<int32_t>()>;
+
+  /// Try to combine G_SHUFFLE_VECTOR into more efficient opcodes.
   /// Returns true if MI changed.
   ///
   /// \pre MI.getOpcode() == G_SHUFFLE_VECTOR.

llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp

@@ -42,6 +42,8 @@
 #include "llvm/Support/MathExtras.h"
 #include "llvm/Target/TargetMachine.h"
 #include <cmath>
+#include <cstdint>
+#include <functional>
 #include <optional>
 #include <tuple>
 
@@ -384,6 +386,19 @@ void CombinerHelper::applyCombineShuffleConcat(MachineInstr &MI,
   MI.eraseFromParent();
 }
 
+// Create a stream from 0 to n with a specified number of steps
+CombinerHelper::GeneratorType
+adderGenerator(const int32_t From, const int32_t To, const int32_t StepSize) {
+  int32_t Counter = From;
+  return [Counter, To, StepSize]() mutable {
+    std::optional<int32_t> OldCount = std::optional<int32_t>(Counter);
+    Counter += StepSize;
+    if (OldCount == (To + StepSize))
+      OldCount = {};
+    return OldCount;
+  };
+}
+
 bool CombinerHelper::tryCombineShuffleVector(MachineInstr &MI) {
   SmallVector<Register, 4> Ops;
   if (matchCombineShuffleVector(MI, Ops)) {