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cpu-minor: Fix for minor CPU scoreboard

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When the scoreboard checks RAW dependency, it determines whether
the source registers can be forwarded or not to evaluate
relative latency. To do that, fuIndices[index] should be used
as an index for accessing cant_forward_from_fu_indices, not register
index itself. Moreover, since fuIndices[index] is cleared as -1
by clearInstDests(), the first compare should be fuIndices[index] != -1
instead of 1.

Change-Id: Ic62546855a8ad5365064d2ea2e2a0fbc1ccc6f41
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/50287
Reviewed-by: ZHENGRONG WANG <seanyukigeek@gmail.com>
Maintainer: ZHENGRONG WANG <seanyukigeek@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
This commit is contained in:
Daecheol You
2021-09-13 19:43:51 +09:00
parent 649ab2dc98
commit fac84c1fe5
2 changed files with 7 additions and 5 deletions
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9
src/cpu/minor/scoreboard.cc
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@@ -195,7 +195,7 @@ Scoreboard::clearInstDests(MinorDynInstPtr inst, bool clear_unpredictable)
if (numResults[index] == 0) {
returnCycle[index] = Cycles(0);
writingInst[index] = 0;
fuIndices[index] = -1;
fuIndices[index] = invalidFUIndex;
}
DPRINTF(MinorScoreboard, "Clearing inst: %s"
@@ -245,10 +245,11 @@ Scoreboard::canInstIssue(MinorDynInstPtr inst,
unsigned short int index;
if (findIndex(reg, index)) {
bool cant_forward = fuIndices[index] != 1 &&
int src_reg_fu = fuIndices[index];
bool cant_forward = src_reg_fu != invalidFUIndex &&
cant_forward_from_fu_indices &&
index < cant_forward_from_fu_indices->size() &&
(*cant_forward_from_fu_indices)[index];
src_reg_fu < cant_forward_from_fu_indices->size() &&
(*cant_forward_from_fu_indices)[src_reg_fu];
Cycles relative_latency = (cant_forward ? Cycles(0) :
(src_index >= num_relative_latencies ?

3
src/cpu/minor/scoreboard.hh
View File

@@ -96,6 +96,7 @@ class Scoreboard : public Named
/** Index of the FU generating this result */
std::vector<int> fuIndices;
static constexpr int invalidFUIndex = -1;
/** The estimated cycle number that the result will be presented.
* This can be offset from to allow forwarding to be simulated as
@@ -121,7 +122,7 @@ class Scoreboard : public Named
zeroReg(reg_classes.at(IntRegClass).zeroReg()),
numResults(numRegs, 0),
numUnpredictableResults(numRegs, 0),
fuIndices(numRegs, 0),
fuIndices(numRegs, invalidFUIndex),
returnCycle(numRegs, Cycles(0)),
writingInst(numRegs, 0)
{ }