[CIR][CodeGen] Handling multiple stmt followed after a switch case

[ChuanqiXu9]

Close #876

We've already considered the case that there are random stmt after a switch case:

for (auto *c : compoundStmt->body()) {
      if (auto *switchCase = dyn_cast<SwitchCase>(c)) {
        res = buildSwitchCase(*switchCase, condType, caseAttrs);
      } else if (lastCaseBlock) {
        // This means it's a random stmt following up a case, just
        // emit it as part of previous known case.
        mlir::OpBuilder::InsertionGuard guardCase(builder);
        builder.setInsertionPointToEnd(lastCaseBlock);
        res = buildStmt(c, /*useCurrentScope=*/!isa<CompoundStmt>(c));
      } else {
        llvm_unreachable("statement doesn't belong to any case region, NYI");
      }

      lastCaseBlock = builder.getBlock();

      if (res.failed())
        break;
}

However, maybe this is an oversight, in the branch of if (lastCaseBlock), the insertion point will be updated automatically when the RAII object guardCase destroys, then we can assign the correct value for lastCaseBlock later. So we will see the weird code pattern in the issue side.

BTW, I found the codes in CIRGenStmt.cpp are far more less similar with the ones other code gen places. Is this intentional? And what is the motivation and guide lines here?

[bcardosolopes]

Thanks for fixing this, awesome!

BTW, I found the codes in CIRGenStmt.cpp are far more less similar with the ones other code gen places. Is this intentional? And what is the motivation and guide lines here?

Structured control flow diverges a bit from the basic block dance of OG, so this ends up being a bit different. Some of it might have been due to some technical debt from early project days too. If you want to refactor it to make it more like OG that's also a welcome change, but I won't ask you to do that as a prereq, thanks for fixing this.

[bcardosolopes]

LGTM