Summary:
The new rules are straightforward. The main rules to keep in mind
are:
1. NAME is an implicit template argument of class and multiclass,
and will be substituted by the name of the instantiating def/defm.
2. The name of a def/defm in a multiclass must contain a reference
to NAME. If such a reference is not present, it is automatically
prepended.
And for some additional subtleties, consider these:
3. defm with no name generates a unique name but has no special
behavior otherwise.
4. def with no name generates an anonymous record, whose name is
unique but undefined. In particular, the name won't contain a
reference to NAME.
Keeping rules 1&2 in mind should allow a predictable behavior of
name resolution that is simple to follow.
The old "rules" were rather surprising: sometimes (but not always),
NAME would correspond to the name of the toplevel defm. They were
also plain bonkers when you pushed them to their limits, as the old
version of the TableGen test case shows.
Having NAME correspond to the name of the toplevel defm introduces
"spooky action at a distance" and breaks composability:
refactoring the upper layers of a hierarchy of nested multiclass
instantiations can cause unexpected breakage by changing the value
of NAME at a lower level of the hierarchy. The new rules don't
suffer from this problem.
Some existing .td files have to be adjusted because they ended up
depending on the details of the old implementation.
Change-Id: I694095231565b30f563e6fd0417b41ee01a12589
Reviewers: tra, simon_tatham, craig.topper, MartinO, arsenm, javed.absar
Subscribers: wdng, llvm-commits
Differential Revision: https://reviews.llvm.org/D47430
llvm-svn: 333900
Summary:
Instantiating def's and defm's needs to perform the following steps:
- for defm's, clone multiclass def prototypes and subsitute template args
- for def's and defm's, add subclass definitions, substituting template
args
- clone the record based on foreach loops and substitute loop iteration
variables
- override record variables based on the global 'let' stack
- resolve the record name (this should be simple, but unfortunately it's
not due to existing .td files relying on rather silly implementation
details)
- for def(m)s in multiclasses, add the unresolved record as a multiclass
prototype
- for top-level def(m)s, resolve all internal variable references and add
them to the record keeper and any active defsets
This change streamlines how we go through these steps, by having both
def's and defm's feed into a single addDef() method that handles foreach,
final resolve, and routing the record to the right place.
This happens to make foreach inside of multiclasses work, as the new
test case demonstrates. Previously, foreach inside multiclasses was not
forbidden by the parser, but it was de facto broken.
Another side effect is that the order of "instantiated from" notes in error
messages is reversed, as the modified test case shows. This is arguably
clearer, since the initial error message ends up pointing directly to
whatever triggered the error, and subsequent notes will point to increasingly
outer layers of multiclasses. This is consistent with how C++ compilers
report nested #includes and nested template instantiations.
Change-Id: Ica146d0db2bc133dd7ed88054371becf24320447
Reviewers: arsenm, craig.topper, tra, MartinO
Subscribers: wdng, llvm-commits
Differential Revision: https://reviews.llvm.org/D44478
llvm-svn: 328117
