[LLVMdev] recognizing DTORs and vptr updates in LLVM.

[Kostya Serebryany]

Hello,

While instrumenting LLVM IR in ThreadSanitizer (race detector), I need
to distinguish between a store to vtable pointer (vptr) and any other
regular store.
This special treatment should be limited to class DTORs, so I should also
know when a function is a DTOR.
Rationale: need to distinguish benign and harmful races on vptr (
http://code.google.com/p/data-race-test/wiki/PopularDataRaces#Data_race_on_vptr
).

Currently, I can figure out when a function is a DTOR and when a store
touches vptr by analyzing mangled names.
_ZN1BD1Ev=="B::~B()"
_ZTV1B=="vtable for B"

define linkonce_odr void @_ZN1BD1Ev(%struct.B* %this) unnamed_addr nounwind
uwtable align 2 {
entry:
  ....
  store i32 (...)** bitcast (i8** getelementptr inbounds ([5 x i8*]*
@_ZTV1B, i64 0, i64 2) to i32 (...)**), i32 (...)*** %0, align 8

However, this does not sound right.
What would be the right way to pass this information from clang to LLVM?
Will using metadata for this purpose be a right solution?
(insn-level metadata for vptr store and module-level metadata for DTORs)


Thanks,

--kcc
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