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[BOLT] Introduce BinaryFunction::canClone() #138771

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[BOLT] Introduce BinaryFunction::canClone() #138771

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5 changes: 5 additions & 0 deletions bolt/include/bolt/Core/BinaryFunction.h
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Expand Up @@ -1375,6 +1375,11 @@ class BinaryFunction {
/// Return true if the function should not have associated symbol table entry.
bool isAnonymous() const { return IsAnonymous; }

/// Return true if we can allow the execution of the original body of the
/// function together with its rewritten copy. This means, e.g., that metadata
/// associated with the function can be duplicated/cloned.
bool canClone() const;

/// If this function was folded, return the function it was folded into.
BinaryFunction *getFoldedIntoFunction() const { return FoldedIntoFunction; }

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10 changes: 10 additions & 0 deletions bolt/lib/Core/BinaryFunction.cpp
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Expand Up @@ -3744,6 +3744,16 @@ void BinaryFunction::postProcessBranches() {
assert(validateCFG() && "invalid CFG");
}

bool BinaryFunction::canClone() const {
// For instrumentation, we need to restrict the execution to the rewritten
// version of the function.
if (opts::Instrument)
return false;

// Check for the presence of metadata that cannot be duplicated.
return !hasEHRanges() && !hasSDTMarker() && !hasPseudoProbe() && !hasORC();
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These checks seem quite restrictive (especially pseudo probes that are supposed to be in every function), what are the functions that can be cloned?

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I expect only tiny leaf function to be cloned, everything else should be patched.

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Note that I'm missing the practical details here.

What happens if we clone the pseudo-probes as well? Since they are uuids for blocks, would the cloned blocks also be identified as the original ones?

And if we don't clone them, are users expected to rely on pseudo-probes after a binary has been bolted?

}

MCSymbol *BinaryFunction::addEntryPointAtOffset(uint64_t Offset) {
assert(Offset && "cannot add primary entry point");
assert(CurrentState == State::Empty || CurrentState == State::Disassembled);
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2 changes: 1 addition & 1 deletion bolt/lib/Passes/PatchEntries.cpp
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Expand Up @@ -65,7 +65,7 @@ Error PatchEntries::runOnFunctions(BinaryContext &BC) {
continue;

// Check if we can skip patching the function.
if (!opts::ForcePatch && !Function.hasEHRanges() &&
if (!opts::ForcePatch && Function.canClone() &&
Function.getSize() < PatchThreshold)
continue;

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