[RISCV] Fix a potential issue in shouldInsertFixupForCodeAlign()

[edward-jones]

Summary

The bool result of shouldInsertExtraNopBytesForCodeAlign() is not checked but the returned nop count is unconditionally read even though it could be uninitialized.

[asb]

Good catch, thanks!

[edward-jones]

Rebased

llvm/trunk/lib/Target/RISCV/MCTargetDesc/RISCVAsmBackend.cpp

 // transfer to R_RISCV_ALIGN relocation type.
 bool RISCVAsmBackend::shouldInsertFixupForCodeAlign(MCAssembler &Asm,
                                                     const MCAsmLayout &Layout,
                                                     MCAlignFragment &AF) {
   // Insert the fixup only when linker relaxation enabled.
   if (!STI.getFeatureBits()[RISCV::FeatureRelax])
     return false;
 
-  // Calculate total Nops we need to insert.
+  // Calculate total Nops we need to insert. If there are none to insert
+  // then simply return.
   unsigned Count;
-  shouldInsertExtraNopBytesForCodeAlign(AF, Count);
-  // No Nop need to insert, simply return.
-  if (Count == 0)
+  if (!shouldInsertExtraNopBytesForCodeAlign(AF, Count) || (Count == 0))
     return false;
 
   MCContext &Ctx = Asm.getContext();
   const MCExpr *Dummy = MCConstantExpr::create(0, Ctx);
   // Create fixup_riscv_align fixup.
   MCFixup Fixup =
       MCFixup::create(0, Dummy, MCFixupKind(RISCV::fixup_riscv_align), SMLoc());