[RISCV][GlobalISel] Preserve Zbb sign extensions

2 files changed, 6 insertions, 1 deletions

diff --git a/backend/lib/Target/RISCV/GISel/RISCVLegalizerInfo.cpp b/backend/lib/Target/RISCV/GISel/RISCVLegalizerInfo.cpp
index 975fc9b..06eea7b 100644
--- a/backend/lib/Target/RISCV/GISel/RISCVLegalizerInfo.cpp
+++ b/backend/lib/Target/RISCV/GISel/RISCVLegalizerInfo.cpp
@@ -284,7 +284,7 @@ foldConstantExtension(MachineInstr &Instruction, MachineFunction &Function, Gene
 
 } // namespace
 
-RISCVLegalizerInfo::RISCVLegalizerInfo(const RISCVSubtarget &Subtarget) {
+RISCVLegalizerInfo::RISCVLegalizerInfo(const RISCVSubtarget &Subtarget) : Subtarget(Subtarget) {
   const LowLevelType S8 = *LowLevelType::makeCategoryNeutralScalar(8);
   const LowLevelType S16 = *LowLevelType::makeCategoryNeutralScalar(16);
   const LowLevelType S32 = *LowLevelType::makeCategoryNeutralScalar(32);
@@ -754,6 +754,8 @@ Expected<void> RISCVLegalizerInfo::legalizeCustom(LegalizerHelper &Helper,
       return std::unexpected(DestinationType.error());
     if (DestinationType->minimumBitWidth() == 64 && *Size == 32)
       return {};
+    if (Subtarget.features().has(RISCVExtension::Zbb) && (*Size == 8 || *Size == 16))
+      return {};
     return Helper.lower(Instruction, LegalizationDecision{
                                          .Action = LegalizationAction::Lower,
                                          .TypeIndex = 0,
diff --git a/backend/lib/Target/RISCV/GISel/RISCVLegalizerInfo.h b/backend/lib/Target/RISCV/GISel/RISCVLegalizerInfo.h
index 7e84764..43a18a1 100644
--- a/backend/lib/Target/RISCV/GISel/RISCVLegalizerInfo.h
+++ b/backend/lib/Target/RISCV/GISel/RISCVLegalizerInfo.h
@@ -18,6 +18,9 @@ public:
                                                  MachineInstr &Instruction) const override;
   [[nodiscard]] bool isSExtCheaperThanZExt(LowLevelType SourceType,
                                            LowLevelType DestinationType) const override;
+
+private:
+  const RISCVSubtarget &Subtarget;
 };
 
 } // namespace rcc::riscv