System for store to load forwarding of individual bytes from sep

Details System for store to load forwarding of individual bytes from sep System for store to load forwarding of individual bytes from sep

1998-09-22

2000-10-31

Ellis, Richard L.

Electrical computers and digital processing systems: processing

Processing control

Processing control for data transfer

712218, 711138, G06F 938

Patent

active

061417475

ABSTRACT:
A load/store unit searches a store queue included therein for each byte accessed by the load independently from the other bytes, and determines the most recent store (in program order) to update that byte. Accordingly, even if one or more bytes accessed by the load are modified by one store while one or more other bytes accessed by the load are modified by another store, the forwarding mechanism may assemble the bytes accessed by the load. More particularly, load data may be forwarded accurately from an arbitrary number of stores. In other words, forwarding may occur up to N stores (where N is the number of bytes accessed by the load). In one particular embodiment, the load/store unit generates a bit vector from a predetermined set of least significant bits of the addresses of loads and stores. The bit vector includes a bit for each byte in a range defined by the number of least significant bits. The bit indicates whether or not the byte is updated (for store bit vectors) or accessed (for load bit vectors). The load/store unit may then examine the bit vectors (and compare the remaining bits of the store and load addresses, exclusive of the least significant bits used to generate the bit vectors) in order to locate the most recent update of each byte.

REFERENCES:
patent: 5471598 (1995-11-01), Quattromani et al.
patent: 5606670 (1997-02-01), Abramson et al.
patent: 5802588 (1998-09-01), Ramagopal et al.
patent: 5832297 (1998-11-01), Ramagopal et al.
patent: 5835747 (1998-11-01), Trull
patent: 6021485 (2000-02-01), Feiste et al.
International Search Report for Application No. PCT/US99/07332 mailed Jul. 19, 1999.

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