IBM PowerPC 604 User Manual page 258

Eight Source Operand Register Numbers
SCIU1 - - •
SCIU2--•
MCIU3--•
LSU--•
2:1 MUX (8)
32bitx8
Figure 6-13. GPR Rename Register
When an integer instruction is dispatched, its source operands are searched simultaneously
from the GPR file and its rename buffer. If a value is found in the rename buffer, that value
is used; otherwise, the value is read from the GPR. However, the rename buffer entry may
not yet
be
valid if the instruction that updates the GPR has not yet executed. In this case,
the instruction is dispatched with the rename buff er entry identifier in place of the operand,
which will
be
supplied by the reservation station when the result is produced. The GPR file
and its rename buffer have eight read ports for source operands to support dispatching of
four integer instructions each cycle.
The FPR file has 32 registers of 64 bits wide and an eight-entry rename buffer. The FPR file
and its rename buffer have three read
ports
for three source operands, which allow one
floating-point instruction to
be
dispatched per cycle.
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PowerPC 604 RISC Microprocessor User's Manual