[llvm-objcopy] IHexELFBuilder::addDataSections - fix evaluation ordering static analyzer warning

[RKSimon]

Summary

As detailed on https://pvs-studio.com/en/blog/posts/cpp/0771/ and raised on D62583, the SecNo++increment is not guaranteed to occur before the second use of SecNo in the same addSection() call.

This patch pulls out the increment and adjusts the second use of SecNo accordingly.

[ikudrin]

llvm/tools/llvm-objcopy/ELF/Object.cpp

1345

This change is irrelevant to the issue.

1352

Object::sortSections() uses llvm::stable_sort(), thus, you may just pass a constant, e.g. 0, as the last argument.

[ikudrin]

llvm/tools/llvm-objcopy/ELF/Object.cpp

1348

Please add a note that passing a constant is allowed because sections are sorted with stable_sort().

1353

It looks like there is no more need to extract the increment as a separate statement because SecNo is now used only once in the expression. But if you find it more readable (and I do), please keep it as is.

llvm/tools/llvm-objcopy/ELF/Object.cpp

void IHexELFBuilder::addDataSections() {
   for (const IHexRecord &R : Records) {
     uint64_t RecAddr;
     switch (R.Type) {
     case IHexRecord::Data:
       // Ignore empty data records
       if (R.HexData.empty())
         continue;
       RecAddr = R.Addr + SegmentAddr + BaseAddr;
-      if (!Section || Section->Addr + Section->Size != RecAddr)
+      if (!Section || Section->Addr + Section->Size != RecAddr) {
         // OriginalOffset field is only used to sort section properly, so
-        // instead of keeping track of real offset in IHEX file, we use
-        // section number.
+        // instead of keeping track of real offset in IHEX file, and as
+        // Object::sortSections() uses llvm::stable_sort(), we can just set to a
+        // constant (zero).
         Section = &Obj->addSection<OwnedDataSection>(
-            ".sec" + std::to_string(SecNo++), RecAddr,
-            ELF::SHF_ALLOC | ELF::SHF_WRITE, SecNo);
+            ".sec" + std::to_string(SecNo), RecAddr,
+            ELF::SHF_ALLOC | ELF::SHF_WRITE, 0);
+        SecNo++;
+      }
       Section->appendHexData(R.HexData);
       break;
     case IHexRecord::EndOfFile:
       break;
     case IHexRecord::SegmentAddr:
       // 20-bit segment address.
       SegmentAddr = checkedGetHex<uint16_t>(R.HexData) << 4;
       break;