Dear LLVM devs,
I’m working on a project in which I need to associate some Values with LLVM Debug Info.
LLVM provides methods to easily iterate over both def-use and use-def chains
of a Value, but I’m having a problem when some of these Users is a debug intrisic.
I have the following situation
92 %call.i = tail call noalias dereferenceable_or_null(16) i8* @malloc(i64 16) #3, !dbg !90
93 %2 = bitcast i8* %call.i to %struct.Node*, !dbg !86
94 call void @llvm.dbg.value(metadata %struct.Node* %2, metadata !24, metadata !DIExpression()) #3, !dbg !89
If I iterate over the users of the value %2 (line 92), I cannot get the
debug instruction at line 94. Knowing that the value is used by metadata,
(method isUsedByMetadata returns true), is it possible to get the debug intrinsic
that uses value %2? Or this does not configure a Use of %2?
Any help would be appreciated.
Best regards,
Hi José,
If I iterate over the users of the value %2 (line 92), I cannot get the
debug instruction at line 94. Knowing that the value is used by metadata,
(method isUsedByMetadata returns true), is it possible to get the debug intrinsic
that uses value %2? Or this does not configure a Use of %2?
There's a helper function "findDbgValues" in
llvm/lib/Transforms/Utils/Local.cpp which should do exactly what you
want, producing a collection of dbg.value intrinsics for a given
Value.
If you need to do something more complicated: as that function shows
the extra step you're missing is calling MetadataAsValue::getIfExists.
As far as I understand it, by design there's no mapping back from one
metadata node to its users: debug info metadata hangs everything off a
unique MetadataAsValue and tries to look it up directly. Value users
of MetadataAsValue can then be looked up in the usual way.
Hi Jeremy,
There’s a helper function “findDbgValues” in
llvm/lib/Transforms/Utils/Local.cpp which should do exactly what you
want, producing a collection of dbg.value intrinsics for a given
Value.
Thanks a lot! This function does exactly what I need.
Best regards,