[RISCV] Don't delete all fixups in RISCVMCCodeEmitter::expandLongCondBr. (#109513)

The Fixups vector passed into this function may already have fixups in
it from earlier instructions. We should not erase those. We just want to
erase fixups added by this function.

Fixes #108612.

(cherry picked from commit c3d3cef)

Author: topperc

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

@@ -283,13 +283,18 @@ void RISCVMCCodeEmitter::expandLongCondBr(const MCInst &MI,
     Offset = 4;
   }
 
+  // Save the number fixups.
+  size_t FixupStartIndex = Fixups.size();
+
   // Emit an unconditional jump to the destination.
   MCInst TmpInst =
       MCInstBuilder(RISCV::JAL).addReg(RISCV::X0).addOperand(SrcSymbol);
   uint32_t Binary = getBinaryCodeForInstr(TmpInst, Fixups, STI);
   support::endian::write(CB, Binary, llvm::endianness::little);
 
-  Fixups.clear();
+  // Drop any fixup added so we can add the correct one.
+  Fixups.resize(FixupStartIndex);
+
   if (SrcSymbol.isExpr()) {
     Fixups.push_back(MCFixup::create(Offset, SrcSymbol.getExpr(),
                                      MCFixupKind(RISCV::fixup_riscv_jal),

llvm/test/MC/RISCV/rv64-relax-all.s

@@ -14,3 +14,9 @@ c.beqz a0, NEAR
 # INSTR:           c.j    0x0 <NEAR>
 # RELAX-INSTR:     jal    zero, 0x0 <NEAR>
 c.j NEAR
+
+bnez s0, .foo
+j    .foo
+beqz s0, .foo
+.foo:
+ret