[RISCV] Check subtarget feature in getBrCond (#129859)

The function currently only checks to see if we compare against an
immediate before selecting the two branch immediate instructions that
are a part of the XCVbi vendor extension. This works at the moment since
there are no other extensions that have a branch immediate instruction.
It would be better if we explicitly check if the XCVbi extension is enabled
before returning the appropriate instruction.

This is also done in preparation for the branch immediate instructions
that are a part of the Xqcibi vendor extension from Qualcomm.

Author: svs-quic

llvm/lib/Target/RISCV/GISel/RISCVInstructionSelector.cpp

@@ -789,7 +789,7 @@ bool RISCVInstructionSelector::select(MachineInstr &MI) {
     RISCVCC::CondCode CC;
     getOperandsForBranch(MI.getOperand(0).getReg(), CC, LHS, RHS, *MRI);
 
-    auto Bcc = MIB.buildInstr(RISCVCC::getBrCond(CC), {}, {LHS, RHS})
+    auto Bcc = MIB.buildInstr(RISCVCC::getBrCond(STI, CC), {}, {LHS, RHS})
                    .addMBB(MI.getOperand(1).getMBB());
     MI.eraseFromParent();
     return constrainSelectedInstRegOperands(*Bcc, TII, TRI, RBI);

llvm/lib/Target/RISCV/RISCVInstrInfo.cpp

@@ -953,14 +953,23 @@ static void parseCondBranch(MachineInstr &LastInst, MachineBasicBlock *&Target,
   Cond.push_back(LastInst.getOperand(1));
 }
 
-unsigned RISCVCC::getBrCond(RISCVCC::CondCode CC, bool Imm) {
+unsigned RISCVCC::getBrCond(const RISCVSubtarget &STI, RISCVCC::CondCode CC,
+                            bool Imm) {
   switch (CC) {
   default:
     llvm_unreachable("Unknown condition code!");
   case RISCVCC::COND_EQ:
-    return Imm ? RISCV::CV_BEQIMM : RISCV::BEQ;
+    if (!Imm)
+      return RISCV::BEQ;
+    if (STI.hasVendorXCVbi())
+      return RISCV::CV_BEQIMM;
+    llvm_unreachable("Unknown branch immediate!");
   case RISCVCC::COND_NE:
-    return Imm ? RISCV::CV_BNEIMM : RISCV::BNE;
+    if (!Imm)
+      return RISCV::BNE;
+    if (STI.hasVendorXCVbi())
+      return RISCV::CV_BNEIMM;
+    llvm_unreachable("Unknown branch immediate!");
   case RISCVCC::COND_LT:
     return RISCV::BLT;
   case RISCVCC::COND_GE:
@@ -974,7 +983,7 @@ unsigned RISCVCC::getBrCond(RISCVCC::CondCode CC, bool Imm) {
 
 const MCInstrDesc &RISCVInstrInfo::getBrCond(RISCVCC::CondCode CC,
                                              bool Imm) const {
-  return get(RISCVCC::getBrCond(CC, Imm));
+  return get(RISCVCC::getBrCond(STI, CC, Imm));
 }
 
 RISCVCC::CondCode RISCVCC::getOppositeBranchCondition(RISCVCC::CondCode CC) {

llvm/lib/Target/RISCV/RISCVInstrInfo.h

@@ -45,7 +45,7 @@ enum CondCode {
 };
 
 CondCode getOppositeBranchCondition(CondCode);
-unsigned getBrCond(CondCode CC, bool Imm = false);
+unsigned getBrCond(const RISCVSubtarget &STI, CondCode CC, bool Imm = false);
 
 } // end of namespace RISCVCC