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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - duplicate llc -mcpu=help for some architectures"
href="https://bugs.llvm.org/show_bug.cgi?id=34331">34331</a>
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<th>Summary</th>
<td>duplicate llc -mcpu=help for some architectures
</td>
</tr>
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<th>Product</th>
<td>new-bugs
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>All
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>new bugs
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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</tr>
<tr>
<th>Reporter</th>
<td>ys114321@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
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<pre>When adding llc -mcpu=help support to BPF, I found when the help output is
printed twice. Through some code study, I found the root cause in the below:
llvm:lib/Target/BPF/BPFTargetMachine.cpp:
BPFTargetMachine::BPFTargetMachine(const Target &T, const Triple &TT,
StringRef CPU, StringRef FS,
const TargetOptions &Options,
Optional<Reloc::Model> RM,
Optional<CodeModel::Model> CM,
CodeGenOpt::Level OL, bool JIT)
: LLVMTargetMachine(T, computeDataLayout(TT), TT, CPU, FS, Options,
getEffectiveRelocModel(RM), getEffectiveCodeModel(CM),
OL),
TLOF(make_unique<TargetLoweringObjectFileELF>()),
Subtarget(TT, CPU, FS, *this) {
initAsmInfo();
}
Both Subtarget constructor and initAsmInfo will eventually create a
MCSubtargetInfo, which calls InitMCProcessorInfo.
void MCSubtargetInfo::InitMCProcessorInfo(StringRef CPU, StringRef FS) {
FeatureBits = getFeatures(CPU, FS, ProcDesc, ProcFeatures);
if (!CPU.empty())
CPUSchedModel = &getSchedModelForCPU(CPU);
else
CPUSchedModel = &MCSchedModel::GetDefaultSchedModel();
}
If you have -mcpu=help in your command line
llc -march=<> -mcpu=help ...
The help information will be printed out twice because getFeatures will
printout
the help info if both ProcDesc and ProcFeatures are not empty.
Checked a few other architectures. X86 and ARM do not have this issue.
Lanai may have this issue as well:
LanaiTargetMachine::LanaiTargetMachine(const Target &T, const Triple &TT,
StringRef Cpu, StringRef FeatureString,
const TargetOptions &Options,
Optional<Reloc::Model> RM,
Optional<CodeModel::Model> CodeModel,
CodeGenOpt::Level OptLevel, bool JIT)
: LLVMTargetMachine(T, computeDataLayout(), TT, Cpu, FeatureString,
Options,
getEffectiveRelocModel(RM),
getEffectiveCodeModel(CodeModel), OptLevel),
Subtarget(TT, Cpu, FeatureString, *this, Options, getCodeModel(),
OptLevel),
TLOF(new LanaiTargetObjectFile()) {
initAsmInfo();
}
It is a lower priority bug as it does not really affect core functionality.</pre>
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