Replace the nested if-else branch-analysis architecture with a flat DFA
model using CodeGen.emitFlat — a single DFS walk emitting each block as
a C label followed by its code and gotos to all successors.
Removed:
- _branchDescendants / emitBranch / generateCallWithError
- _generateCallWithError, _noWalkNext, _genVisited
- generateNextCode, findBackEdges
- WCDecision._branchDescendants / _emitBranch / overridden generateCode
Added:
- CodeGen.emitFlat(entry) — flat DFS emit with labels + gotos
- WCBlock.generateFlowCode() — base emits gotos from wcNextFlow
- WCDecision.generateFlowCode() — if-goto / goto for decisions
- WCProcCall.generateFlowCode() — if (call != 0) goto err / goto ok
Output is flat — zero nested if-else for branch/error handling.
Tests use local out/ directory.