The code snippet below is from the function fetch() in o3/fetch_impl.hh.
// If we're branching after this instruction, quite fetching
// from the same block then.
predictedBranch |= thisPC.branching();
predictedBranch |=
lookupAndUpdateNextPC(instruction, nextPC);
if (predictedBranch) {
DPRINTF(Fetch, "Branch detected with PC = %s\n", thisPC);
}
newMacro |= thisPC.instAddr() != nextPC.instAddr();
// Move to the next instruction, unless we have a branch.
thisPC = nextPC;
There are a couple of things that I am not clear about.
1. From reading that trace, it seems that the PC can jump in to the
microcodedRom on a branch. For example the instruction JMP_FAR_M in x86
makes a CPU jump in to microcodedRom. In this case, I think the newMacro
variable will not be updated, since only the microPC changes and not the
instruction address. So, should the newMacro be set to true even in this
case?
2. Since the PC may have been changed, should the variable inRom be
re-assigned? As observed above, an instruction can make the PC jump to a
position in ROM.
Thanks
Nilay
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