gac43 at cam.ac.uk
Tue Jan 19 06:57:42 PST 2010
I was wondering if someone could explain precisely what the
ComplexPattern tablegen class does?
Here's the first line of the definition (from TargetSelectionDAG.td) for
class ComplexPattern<ValueType ty, int numops, string fn,
list<SDNode> roots = ,
list<SDNodeProperty> props = ,
list<CPAttribute> attrs = >
As far as I can tell it gives the name of a selection function (fn) that
will be called to match that particular ComplexPattern. Should that
function return true that pattern has matched. The match function can
also fill in some operands that can be used later on (Number is
specified by numops), ty presumably specifies the type of node that this
match can be attempted on. Is my understanding of this correct?
The thing I'm still unsure about is roots, what exactly does this do?
The comment above the definition specifies that 'RootNodes are the list
of possible root nodes of the sub-dags to match' (RootsNodes is assigned
to root so they're the same) but I can't make any sense of this.
More information about the llvm-dev