A MachRep is the representation of a value in Cmm. It is used for resource allocation: eg. which kind of register a value should be stored in.

The primary requirement is that there exists a function

cmmExprRep :: CmmExpr -> MachRep

This means that:

• a register has an implicit MachRep - a literal has an implicit MachRep - an operation (MachOp) has an implicit result MachRep

It also means that we can check that the arguments to a MachOp have the correct MachRep, i.e. we can do a kind of lint-style type checking on Cmm.

Machine-level primops; ones which we can reasonably delegate to the native code generators to handle. Basically contains C's primops and no others.

Nomenclature: all ops indicate width and signedness, where appropriate. Widths: 8/16/32/64 means the given size, obviously. Nat means the operation works on STG word sized objects. Signedness: S means signed, U means unsigned. For operations where signedness is irrelevant or makes no difference (for example integer add), the signedness component is omitted.

An exception: NatP is a ptr-typed native word. From the point of view of the native code generators this distinction is irrelevant, but the C code generator sometimes needs this info to emit the right casts.