bool MCCodePadder::relaxFragment(MCPaddingFragment *Fragment,
MCAsmLayout &Layout) {
if (!Fragment->isInsertionPoint())
return false;
uint64_t OldSize = Fragment->getSize();
uint64_t MaxWindowSize = getMaxWindowSize(Fragment, Layout);
if (MaxWindowSize == UINT64_C(0))
return false;
assert(isPowerOf2_64(MaxWindowSize) &&
"MaxWindowSize must be an integer power of 2");
uint64_t SectionAlignment = Fragment->getParent()->getAlignment();
assert(isPowerOf2_64(SectionAlignment) &&
"SectionAlignment must be an integer power of 2");
MCPFRange &Jurisdiction = getJurisdiction(Fragment, Layout);
uint64_t OptimalSize = UINT64_C(0);
double OptimalWeight = std::numeric_limits<double>::max();
uint64_t MaxFragmentSize = MaxWindowSize - UINT16_C(1);
for (uint64_t Size = UINT64_C(0); Size <= MaxFragmentSize; ++Size) {
Fragment->setSize(Size);
Layout.invalidateFragmentsFrom(Fragment);
double SizeWeight = 0.0;
// The section is guaranteed to be aligned to SectionAlignment, but that
// doesn't guarantee the exact section offset w.r.t. the policies window
// size.
// As a concrete example, the section could be aligned to 16B, but a
// policy's window size can be 32B. That means that the section actual start
// address can either be 0mod32 or 16mod32. The said policy will act
// differently for each case, so we need to take both into consideration.
for (uint64_t Offset = UINT64_C(0); Offset < MaxWindowSize;
Offset += SectionAlignment) {
double OffsetWeight = std::accumulate(
CodePaddingPolicies.begin(), CodePaddingPolicies.end(), 0.0,
[&Jurisdiction, &Offset, &Layout](
double Weight, const MCCodePaddingPolicy *Policy) -> double {
double PolicyWeight =
Policy->computeRangePenaltyWeight(Jurisdiction, Offset, Layout);
assert(PolicyWeight >= 0.0 && "A penalty weight must be positive");
return Weight + PolicyWeight;
});
SizeWeight = std::max(SizeWeight, OffsetWeight);
}
if (SizeWeight < OptimalWeight) {
OptimalWeight = SizeWeight;
OptimalSize = Size;
}
if (OptimalWeight == 0.0)
break;
}
Fragment->setSize(OptimalSize);
Layout.invalidateFragmentsFrom(Fragment);
return OldSize != OptimalSize;
}
