Previously, subprograms contained a metadata reference to the function they
described. Because most clients need to get or set a subprogram for a given
function rather than the other way around, this created unneeded inefficiency.
For example, many passes needed to call the function llvm::makeSubprogramMap()
to build a mapping from functions to subprograms, and the IR linker needed to
fix up function references in a way that caused quadratic complexity in the IR
linking phase of LTO.
This change reverses the direction of the edge by storing the subprogram as
function-level metadata and removing DISubprogram's function field.
Since this is an IR change, a bitcode upgrade has been provided.
Fixes PR23367. An upgrade script for textual IR for out-of-tree clients is
attached to the PR.
Differential Revision: http://reviews.llvm.org/D14265
llvm-svn: 252219
Add `Function::setSubprogram()` and `Function::getSubprogram()`,
convenience methods to forward to `setMetadata()` and `getMetadata()`,
respectively, and deal in `DISubprogram` instead of `MDNode`.
Also add a verifier check to enforce that `!dbg` attachments are always
subprograms.
Originally (when I had the llvm-dev discussion back in April) I thought
I'd store a pointer directly on `llvm::Function` for these attachments
-- we frequently have debug info, and that's much cheaper than using map
in the context if there are no other function-level attachments -- but
for now I'm just using the generic infrastructure. Let's add the extra
complexity only if this shows up in a profile.
llvm-svn: 246339
Peter Collingbourne