[llvm-dev] StructType --> DICompositeType?

[David Blaikie via llvm-dev]

struct types and DITypes aren't 1:1 - the same struct type might be used
for many DITypes and a single variable (with a single DIType) might be
described by multiple different pieces of memory/registers with different
struct types throughout its lifetime.

The nontrivial mapping from debug info to IR is the only real mapping,
unfortunately. There's no shortcut.

- Dave

On Tue, Jul 24, 2018 at 11:00 AM Troy Johnson via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Right, a GlobalVariable actually has interesting debug metadata attached,
> but if one is dealing with the target type of a pointer operand of a GEP
> that's accessing a structure field, then tracing that back to something
> with debug metadata is nontrivial.  It may not be a GlobalVariable.
>
>
> -Troy
> ------------------------------
> *From:* paul.robinson at sony.com <paul.robinson at sony.com>
> *Sent:* Tuesday, July 24, 2018 12:54:57 PM
> *To:* Troy Johnson
> *Cc:* llvm-dev at lists.llvm.org
> *Subject:* RE: StructType --> DICompositeType?
>
>
> They aren't directly tied together, as a type by its lonesome isn't all
> that interesting to either compilers or debuggers.
>
> But for example a global variable has a link to its DIGlobalVariable,
> which has a link to its DIType, and so you can associate the variable's
> Type with a DIType that way.
>
> --paulr
>
>
>
> *From:* llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] *On Behalf Of *Troy
> Johnson via llvm-dev
> *Sent:* Tuesday, July 24, 2018 11:50 AM
> *To:* llvm-dev at lists.llvm.org
> *Subject:* [llvm-dev] StructType --> DICompositeType?
>
>
>
> Is there a more convenient way to obtain a DIType given a Type than
> matching up the strings for the names?
>
>
>
> For example, given:
>
>
>
> struct S {
>   int x, y;
> } s;
>
> void foo(S *a) {
>   a->x = 0;
>   a->y = 1;
> }
>
>
>
> There are DIType nodes for the struct Type:
>
>
>
> !6 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "S",
> file: !3, line: 1, size: 64, flags: DIFlagTypePassByValue, elements: !7,
> identifier: "_ZTS1S")
> !7 = !{!8, !10}
> !8 = !DIDerivedType(tag: DW_TAG_member, name: "x", scope: !6, file: !3,
> line: 2, baseType: !9, size: 32)
> !9 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
> !10 = !DIDerivedType(tag: DW_TAG_member, name: "y", scope: !6, file: !3,
> line: 2, baseType: !9, size: 32, offset: 32)
>
>
>
> but given just the StructType for S there is no direct way to get to the
> DICompositeType.  I've made something work by prescanning all the DITypes
> in my Module and creating a map that uses type names as the key, being
> careful to strip "struct." prefixes and maintain scoping for nested structs
> (e.g., S1::S2), which works, but seems awfully complicated to need to do.
>
>
>
> Seems like StructType should have a getMetaData() function, but I don't
> see one.
>
>
>
> -Troy
>
>
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