--asan used to force the legacy PhaseB because the instrumentation step was a separate
`opt -passes=forceattrs,asan -force-attribute=sanitize_address -asan-globals=false` child
process. ircore.dll now exposes ircore_mlir_to_obj_asan / ircore_llvmir_to_obj_asan, which
run the same passes through LLVM's C pass builder (LLVMRunPasses) between MLIR lowering and
codegen, so ASan builds also avoid the three child processes.
- the two cl::opt values are parsed once (std::call_once) before the first pass run
- PhaseB loads the asan entry point together with the others and calls it when _asan_mode
is set; the legacy `opt` path stays for --phaseb-legacy and is unchanged
- --traceback (llc -frame-pointer=all) and raw-IR modules (llvm-link/opt) still take the
legacy flow
Verified on a real VKernel module: the ircore-built object and the `opt`-instrumented one
reference the same ASan runtime symbols (69 __asan_report / 4 asan.module_ctor), and a
deliberate heap overflow is reported identically by both builds.
TermiNexus
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