[GlobalISel] Narrow scalar selects

Match LLVM's narrowScalarSelect lowering for wide scalar values. Build widened sources from LLT destinations so CSE hits reuse the actual result register instead of introducing copies.

1 files changed, 2 insertions, 0 deletions

diff --git a/backend/include/rcc/CodeGen/GlobalISel/LegalizerHelper.h b/backend/include/rcc/CodeGen/GlobalISel/LegalizerHelper.h
index 4376f62..993690e 100644
--- a/backend/include/rcc/CodeGen/GlobalISel/LegalizerHelper.h
+++ b/backend/include/rcc/CodeGen/GlobalISel/LegalizerHelper.h
@@ -72,6 +72,8 @@ private:
                                                  LowLevelType NarrowType);
   [[nodiscard]] Expected<void> narrowScalarExt(MachineInstr &Instruction, std::size_t TypeIndex,
                                                LowLevelType NarrowType);
+  [[nodiscard]] Expected<void> narrowScalarSelect(MachineInstr &Instruction, std::size_t TypeIndex,
+                                                  LowLevelType NarrowType);
   [[nodiscard]] Expected<void> widenScalarAddSubOverflow(MachineInstr &Instruction,
                                                          std::size_t TypeIndex,
                                                          LowLevelType WideType);