[PATCH] IR: Make MDNode::dump() useful by adding addresses

[Duncan P. N. Exon Smith]

> On 2014 Dec 12, at 15:47, David Blaikie <dblaikie at gmail.com> wrote:
> 
> 
> 
> On Fri, Dec 12, 2014 at 2:37 PM, Duncan P. N. Exon Smith <dexonsmith at apple.com> wrote:
> It's horrible to inspect `MDNode`s in a debugger.  All of their operands
> that are `MDNode`s get dumped as `<badref>`, since we can't assign
> metadata slots in the context of a `Metadata::dump()`.  (Why not?  Why
> not assign numbers lazily?  Because then each time you called `dump()`,
> a given `MDNode` could have a different lazily assigned number.)
> 
> Fortunately, the C memory model gives us perfectly good identifiers for
> `MDNode`.  Add pointer addresses to the dumps, transforming this:
> 
>     (lldb) e N->dump()
>     metadata !{i32 662302, i32 26, metadata <badref>, null}
> 
>     (lldb) e ((MDNode*)N->getOperand(2))->dump()
>     metadata !{i32 4, metadata !"foo"}
> 
> into:
> 
>     (lldb) e N->dump()
>     metadata !{i32 662302, i32 26, metadata <badref:0x100706ee0>, null}
> 
>     (lldb) e ((MDNode*)0x100706ee0)->dump()
>     metadata !{i32 4, metadata !"foo"}
> 
> and this:
> 
>     (lldb) e N->dump()
>     metadata !{metadata <badref>, metadata <badref>, metadata <badref>, metadata <badref>, metadata <badref>}
> 
>     (lldb) e N->getOperand(0)
>     (const llvm::MDOperand) $0 = {
>       MD = 0x00000001012004e0
>     }
>     (lldb) e N->getOperand(1)
>     (const llvm::MDOperand) $1 = {
>       MD = 0x00000001012004e0
>     }
>     (lldb) e N->getOperand(2)
>     (const llvm::MDOperand) $2 = {
>       MD = 0x0000000101200058
>     }
>     (lldb) e N->getOperand(3)
>     (const llvm::MDOperand) $3 = {
>       MD = 0x00000001012004e0
>     }
>     (lldb) e N->getOperand(4)
>     (const llvm::MDOperand) $4 = {
>       MD = 0x0000000101200058
>     }
>     (lldb) e ((MDNode*)0x00000001012004e0)->dump()
>     metadata !{}
> 
>     (lldb) e ((MDNode*)0x0000000101200058)->dump()
>     metadata !{null}
> 
> into:
> 
>     (lldb) e N->dump()
>     metadata !{metadata <badref:0x1012004e0>, metadata <badref:0x1012004e0>, metadata <badref:0x101200058>, metadata <badref:0x1012004e0>, metadata <badref:0x101200058>}
> 
>     (lldb) e ((MDNode*)0x1012004e0)->dump()
>     metadata !{}
> 
>     (lldb) e ((MDNode*)0x101200058)->dump()
>     metadata !{null}
> 
> I've left `badref` in the operand to keep it `FileCheck`-able, via:
> 
>     CHECK-NOT: badref
> 
> badref seems like a pretty weird anachronism & I don't see any instances of "CHECK.*badref" in 'test' (but it could be under other prefixes)
>  
> 
> Another option would be:
> 
>     (lldb) e N->dump()
>     metadata !{metadata !0x1012004e0, metadata !0x1012004e0, metadata !0x101200058, metadata !0x1012004e0, metadata !0x101200058}
> 
> which would allow:
> 
>     CHECK-NOT: !0x
> 
> I'd just imagine you'd check for "{.*metadata!" - which will be harder in your changes, but still possible I would imagine?
>  
> 
> but IMO that's too subtle...
> 
> Not sure - seems almost less confusing than having 'badref' around.
>  

`badref` is used consistently for `Value`s that don't have an assigned slot,
but now that `Metadata` is separate it can probably do its own thing.

There is only once use in LLVM, not sure about clang:

    $ git grep badref
    Assembler/2010-02-05-FunctionLocalMetadataBecomesNull.ll:; RUN: opt -O3 < %s | llvm-dis | not grep badref

But this test should probably just CHECK for the expected result anyway.

I'm pretty much happy with anything that gives a pointer address.  Here are
some paint colours:

    !{!0, null, <badref>}
    !{!0, null, 0xabc}
    !{!0, null, !0xabc}
    !{!0, null, <0xabc>}
    !{!0, null, !<0xabc>}
    !{!0, null, <badref:0xabc>}

Everyone okay with `!{!0, null, <0xabc>}`?