[RISCV] Store RVC and TSO ELF flags explicitly in RISCVTargetStreamer. NFCI (#83344)

Instead of caching STI in the RISCVELFTargetStreamer, store the two
flags we need from it.

My goal is to allow RISCVAsmPrinter to override these flags using IR
module metadata for LTO. So they need to be separated from the STI used
to construct the TargetStreamer.

This patch should be NFC as long as no one is changing the contents of
the STI that was used to construct the TargetStreamer between the
constructor and the use of the flags.

Author: topperc

llvm/lib/Target/RISCV/MCTargetDesc/RISCVELFStreamer.cpp

@@ -31,12 +31,13 @@ using namespace llvm;
 // This part is for ELF object output.
 RISCVTargetELFStreamer::RISCVTargetELFStreamer(MCStreamer &S,
                                                const MCSubtargetInfo &STI)
-    : RISCVTargetStreamer(S), CurrentVendor("riscv"), STI(STI) {
+    : RISCVTargetStreamer(S), CurrentVendor("riscv") {
   MCAssembler &MCA = getStreamer().getAssembler();
   const FeatureBitset &Features = STI.getFeatureBits();
   auto &MAB = static_cast<RISCVAsmBackend &>(MCA.getBackend());
   setTargetABI(RISCVABI::computeTargetABI(STI.getTargetTriple(), Features,
                                           MAB.getTargetOptions().getABIName()));
+  setFlagsFromFeatures(STI);
   // `j label` in `.option norelax; j label; .option relax; ...; label:` needs a
   // relocation to ensure the jump target is correct after linking. This is due
   // to a limitation that shouldForceRelocation has to make the decision upfront
@@ -87,14 +88,13 @@ void RISCVTargetELFStreamer::finishAttributeSection() {
 void RISCVTargetELFStreamer::finish() {
   RISCVTargetStreamer::finish();
   MCAssembler &MCA = getStreamer().getAssembler();
-  const FeatureBitset &Features = STI.getFeatureBits();
   RISCVABI::ABI ABI = getTargetABI();
 
   unsigned EFlags = MCA.getELFHeaderEFlags();
 
-  if (Features[RISCV::FeatureStdExtC])
+  if (hasRVC())
     EFlags |= ELF::EF_RISCV_RVC;
-  if (Features[RISCV::FeatureStdExtZtso])
+  if (hasTSO())
     EFlags |= ELF::EF_RISCV_TSO;
 
   switch (ABI) {

llvm/lib/Target/RISCV/MCTargetDesc/RISCVELFStreamer.h

@@ -46,7 +46,6 @@ class RISCVTargetELFStreamer : public RISCVTargetStreamer {
   StringRef CurrentVendor;
 
   MCSection *AttributeSection = nullptr;
-  const MCSubtargetInfo &STI;
 
   void emitAttribute(unsigned Attribute, unsigned Value) override;
   void emitTextAttribute(unsigned Attribute, StringRef String) override;

llvm/lib/Target/RISCV/MCTargetDesc/RISCVTargetStreamer.cpp

@@ -48,6 +48,11 @@ void RISCVTargetStreamer::setTargetABI(RISCVABI::ABI ABI) {
   TargetABI = ABI;
 }
 
+void RISCVTargetStreamer::setFlagsFromFeatures(const MCSubtargetInfo &STI) {
+  HasRVC = STI.hasFeature(RISCV::FeatureStdExtC);
+  HasTSO = STI.hasFeature(RISCV::FeatureStdExtZtso);
+}
+
 void RISCVTargetStreamer::emitTargetAttributes(const MCSubtargetInfo &STI,
                                                bool EmitStackAlign) {
   if (EmitStackAlign) {

llvm/lib/Target/RISCV/MCTargetDesc/RISCVTargetStreamer.h

@@ -33,6 +33,8 @@ struct RISCVOptionArchArg {
 
 class RISCVTargetStreamer : public MCTargetStreamer {
   RISCVABI::ABI TargetABI = RISCVABI::ABI_Unknown;
+  bool HasRVC = false;
+  bool HasTSO = false;
 
 public:
   RISCVTargetStreamer(MCStreamer &S);
@@ -58,6 +60,9 @@ class RISCVTargetStreamer : public MCTargetStreamer {
   void emitTargetAttributes(const MCSubtargetInfo &STI, bool EmitStackAlign);
   void setTargetABI(RISCVABI::ABI ABI);
   RISCVABI::ABI getTargetABI() const { return TargetABI; }
+  void setFlagsFromFeatures(const MCSubtargetInfo &STI);
+  bool hasRVC() const { return HasRVC; }
+  bool hasTSO() const { return HasTSO; }
 };
 
 // This part is for ascii assembly output