Duncan P. N. Exon Smith
2014-Dec-05 02:44 UTC
[LLVMdev] [RFC] Semantic changes in the Metadata/Value split
As of Monday, I finally got a preliminary patch passing check and check-clang with the metadata-value split. It's rather massive, but mostly NFC. I've managed to keep the bitcode format, assembly syntax, and C API unchanged, except for a few semantic restrictions that I'll separate out and commit ahead of time via assertions to the extent I can. (Obviously I plan to clean up assembly and bitcode in a follow-up commit.) This is mainly a heads up about what the semantic changes are; I think they're mostly unavoidable given the constraints. - Function-local metadata is restricted to direct arguments to call intrinsics (i.e., `metadata !{i32 %val}`). Temporarily, it's spelled the same way as an `MDNode` in assembly. - Except during "construction" -- for uniquing forward declarations -- `MDNode` does not support `replaceAllUsesWith()`. - When an `MDNode` operand changes and there's a uniquing collision, uniquing is dropped for that node -- it becomes "distinct". (Note that an operand going to null no longer turns off uniquing, unless there's a collision. `MDNode` now supports `dropAllReferences()`, so there's no more web of RAUW during teardown of the context.) - Nodes that self-reference aren't uniqued at all. I've attached my current patch (rebased last night) as a reference. I'll separate out as much as I can before committing the main thing. Aside from adding assertions for the above-mentioned semantic changes, if anyone sees anything obvious to separate out let me know. There are also a few follow-ups that I've left until later: - Change assembly syntax to make metadata look as typeless as it is. (This will come with painful clang testcase updates... yay!) - Ditto for bitcode. - Add assembly syntax, bitcode support, and C++ API for `MDNode::getDistinct()`, which explicitly opts out of uniquing. - Add `MDInt`, which is a generic integer represented by an `APSInt` for use in metadata. - Upgrade various types of metadata to use `MDInt` and/or `getDistinct()`. - Add reference counting semantics to some types of metadata, so that no-longer-referenced metadata gets cleaned up. - Upgrade `DebugLoc` from 8 bits of column info to 16. - ... and get back to the debug info IR changes that get me into this mess :). (I actually tried really hard to get half of this working without the other half. I created the `ValueAsMetadata` bridge and restricted `MDNode` to only have subclasses of `Metadata` as operands, but left `Metadata` inheriting from `Value`. This only took a few days to get compiling, but left tons of errors to be found at runtime due to failing `cast<>` failures. Although there are small things that I can break off, IMO fundamentally splitting up this patch is untenable.) -------------- next part -------------- A non-text attachment was scrubbed... Name: metadata-value-split.patch Type: application/octet-stream Size: 350563 bytes Desc: not available URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20141204/cb7020eb/attachment.obj> -------------- next part -------------- A non-text attachment was scrubbed... Name: metadata-value-split-clang.patch Type: application/octet-stream Size: 68983 bytes Desc: not available URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20141204/cb7020eb/attachment-0001.obj>
Peter Collingbourne
2014-Dec-05 08:39 UTC
[LLVMdev] [RFC] Semantic changes in the Metadata/Value split
On Thu, Dec 04, 2014 at 06:44:36PM -0800, Duncan P. N. Exon Smith wrote:> As of Monday, I finally got a preliminary patch passing check and > check-clang with the metadata-value split.Do you have the Go bindings enabled? Because of the changes you made to the DIBuilder interface, I expect that your changes will break the bindings. I'm happy to help with updating the bindings. Thanks, -- Peter
Duncan P. N. Exon Smith
2014-Dec-05 17:35 UTC
[LLVMdev] [RFC] Semantic changes in the Metadata/Value split
> On 2014-Dec-05, at 00:39, Peter Collingbourne <peter at pcc.me.uk> wrote: > > On Thu, Dec 04, 2014 at 06:44:36PM -0800, Duncan P. N. Exon Smith wrote: >> As of Monday, I finally got a preliminary patch passing check and >> check-clang with the metadata-value split. > > Do you have the Go bindings enabled? Because of the changes you made to the > DIBuilder interface, I expect that your changes will break the bindings.Yes, that's probably true :(. There aren't really any DIBuilder changes, but the split itself will probably cause compile failures. I expect the fixes will be fairly mechanical, along the lines of the changes I made to lib/IR/Core.cpp. I don't see instructions for enabling the bindings on the CMake page [1]. Is there a way to do it? [1]: http://llvm.org/docs/CMake.html (I can compile the bindings on Darwin, right?)> I'm happy to help with updating the bindings.Thanks!
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