The previous approach broke the instantiation convention for templated
substitutions, as we were attempting to instantiate the initializer
even when it was still dependent.
We deferred variable template instantiation until the end of the TU.
However, type deduction requires the initializer immediately,
similar to how constant evaluation does.
Fixes https://github.com/llvm/llvm-project/issues/140773Fixes#135032Fixes#134526
Reapplies https://github.com/llvm/llvm-project/pull/138122
Fixes https://github.com/llvm/llvm-project/issues/135032
Due to nested templates, when instantiating the outer layer (the
template class), the inner layer (the template variable) uses delayed
instantiation.
This causes the declaration (VarDecl) of the template variable to retain
the type from the original template declaration (i.e., auto), and it
loses the initializer.
Later, when instantiating the template variable, its
VarTemplateSpecializationDecl type depends on the VarDecl type.
Thus, the VarTemplateSpecializationDecl also has no initializer, and its
type remains auto.
Ultimately, when building the reference expression in
Sema::BuildDeclarationNameExpr, the expression's type is auto and stays
as auto until code generation, triggering llvm_unreachable in
CodeGenTypes::ConvertType.
Since I noticed that the deduction of auto type is caused by the
initializer
I plan to do special processing for template variables of type auto,
that is, to prevent their delayed instantiation
so that their initializers will not be lost when the outer template
class is instantiated
update the type from the definition even if we didn't instantiate a definition.
We may have instantiated the definition in an earlier stage of semantic
analysis, after creating the DeclRefExpr but before we reach a point where a
complete expression type is required.
llvm-svn: 320709
instantiation declarations if they are usable from constant expressions.
We are permitted to instantiate in these cases, and required to do so in order
to have an initializer available for use within constant evaluation.
llvm-svn: 316136
