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[llvm-mca] Simplify code that computes the latency of an instruction in

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InstrBuilder. NFCI

This was possible because of r327406, which added function`computeInstrLatency`
to MCSchedModel.

llvm-svn: 327415
This commit is contained in:
Andrea Di Biagio 2018-03-13 15:59:59 +00:00
parent 23d099ea06
commit a627e4f7be
1 changed files with 5 additions and 30 deletions
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35
tools/llvm-mca/InstrBuilder.cpp
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@ -123,41 +123,16 @@ initializeUsedResources(InstrDesc &ID, const MCSchedClassDesc &SCDesc,
static void computeMaxLatency(InstrDesc &ID, const MCInstrDesc &MCDesc,
const MCSchedClassDesc &SCDesc,
const MCSubtargetInfo &STI) {
unsigned MaxLatency = 0;
unsigned NumWriteLatencyEntries = SCDesc.NumWriteLatencyEntries;
for (unsigned I = 0, E = NumWriteLatencyEntries; I < E; ++I) {
int Cycles = STI.getWriteLatencyEntry(&SCDesc, I)->Cycles;
// Check if this is an unknown latency. Conservatively (pessimistically)
// assume a latency of 100cy if late.
if (Cycles == -1)
Cycles = 100;
MaxLatency = std::max(MaxLatency, static_cast<unsigned>(Cycles));
}
if (MCDesc.isCall()) {
// We cannot estimate how long this call will take.
// Artificially set an arbitrarily high latency (100cy).
MaxLatency = std::max(100U, MaxLatency);
ID.MaxLatency = 100U;
return;
}
// Check if this instruction consumes any processor resources.
// If the latency is unknown, then conservatively set it equal to the maximum
// number of cycles for a resource consumed by this instruction.
if (!MaxLatency && ID.Resources.size()) {
// Check if this instruction consumes any processor resources.
// If so, then compute the max of the cycles spent for each resource, and
// use it as the MaxLatency.
for (const std::pair<uint64_t, ResourceUsage> &Resource : ID.Resources)
MaxLatency = std::max(MaxLatency, Resource.second.size());
}
if (SCDesc.isVariant() && MaxLatency == 0) {
errs() << "note: unknown latency for a variant opcode. Conservatively"
<< " assume a default latency of 1cy.\n";
MaxLatency = 1;
}
ID.MaxLatency = MaxLatency;
int Latency = MCSchedModel::computeInstrLatency(STI, SCDesc);
// If latency is unknown, then conservatively assume a MaxLatency of 100cy.
ID.MaxLatency = Latency < 0 ? 100U : static_cast<unsigned>(Latency);
}
static void populateWrites(InstrDesc &ID, const MCInst &MCI,