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Julian Seward authored
Get rid of multiple-result MachOps (MO_NatS_AddC, MO_NatS_SubC, MO_NatS_MulC) which implement {add,sub,mul}IntC#. Supporting gunk in the NCG disappears as a result. Instead: * {add,sub}IntC# are translated out during abstract C simplification, turning into the xor-xor-invert-and-shift sequence previously defined in PrimOps.h. * mulIntC# is more difficult to get rid of portably. Instead we have a new single-result PrimOp, mulIntMayOflo, with corresponding MachOp MO_NatS_MulMayOflo. This tells you whether a W x W -> W signed multiply might overflow, where W is the word size. When W=32, is implemented by computing a 2W-long result. When W=64, we use the previous approximation. PrelNum.lhs' implementation of timesInteger changes slightly, to use the new PrimOp.
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