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[NFC][AMDGPU] Refactor handling of amdgpu-synchronize-as MD on fences #148630

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merged 1 commit into from
Jul 24, 2025
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[NFC][AMDGPU] Refactor handling of amdgpu-synchronize-as MD on fences #148630

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32 changes: 19 additions & 13 deletions llvm/lib/Target/AMDGPU/SIMemoryLegalizer.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -705,15 +705,15 @@ void diagnoseUnknownMMRAASName(const MachineInstr &MI, StringRef AS) {
}

/// Reads \p MI's MMRAs to parse the "amdgpu-synchronize-as" MMRA.
/// If this tag isn't present, or if it has no meaningful values, returns \p
/// Default. Otherwise returns all the address spaces concerned by the MMRA.
static SIAtomicAddrSpace getFenceAddrSpaceMMRA(const MachineInstr &MI,
SIAtomicAddrSpace Default) {
/// If this tag isn't present, or if it has no meaningful values, returns
/// \p none, otherwise returns the address spaces specified by the MD.
static std::optional<SIAtomicAddrSpace>
getSynchronizeAddrSpaceMD(const MachineInstr &MI) {
static constexpr StringLiteral FenceASPrefix = "amdgpu-synchronize-as";

auto MMRA = MMRAMetadata(MI.getMMRAMetadata());
if (!MMRA)
return Default;
return std::nullopt;

SIAtomicAddrSpace Result = SIAtomicAddrSpace::NONE;
for (const auto &[Prefix, Suffix] : MMRA) {
Expand All @@ -726,7 +726,10 @@ static SIAtomicAddrSpace getFenceAddrSpaceMMRA(const MachineInstr &MI,
diagnoseUnknownMMRAASName(MI, Suffix);
}

return (Result != SIAtomicAddrSpace::NONE) ? Result : Default;
if (Result == SIAtomicAddrSpace::NONE)
return std::nullopt;

return Result;
}

} // end anonymous namespace
Expand Down Expand Up @@ -903,12 +906,19 @@ SIMemOpAccess::getAtomicFenceInfo(const MachineBasicBlock::iterator &MI) const {
std::tie(Scope, OrderingAddrSpace, IsCrossAddressSpaceOrdering) =
*ScopeOrNone;

if ((OrderingAddrSpace == SIAtomicAddrSpace::NONE) ||
((OrderingAddrSpace & SIAtomicAddrSpace::ATOMIC) != OrderingAddrSpace)) {
if (OrderingAddrSpace != SIAtomicAddrSpace::ATOMIC) {
// We currently expect refineOrderingAS to be the only place that
// can refine the AS ordered by the fence.
// If that changes, we need to review the semantics of that function
// in case it needs to preserve certain address spaces.
reportUnsupported(MI, "Unsupported atomic address space");
return std::nullopt;
}

auto SynchronizeAS = getSynchronizeAddrSpaceMD(*MI);
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nit: no auto

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The type name is quite long and distracting. I think we generally allow auto in such cases, at least we idiomatically use auto with functions like getIConstantVRegValWithLookThrough everywhere in global isel

if (SynchronizeAS)
OrderingAddrSpace = *SynchronizeAS;

return SIMemOpInfo(Ordering, Scope, OrderingAddrSpace, SIAtomicAddrSpace::ATOMIC,
IsCrossAddressSpaceOrdering, AtomicOrdering::NotAtomic);
}
Expand Down Expand Up @@ -2687,11 +2697,7 @@ bool SIMemoryLegalizer::expandAtomicFence(const SIMemOpInfo &MOI,
AtomicPseudoMIs.push_back(MI);
bool Changed = false;

// Refine fenced address space based on MMRAs.
//
// TODO: Should we support this MMRA on other atomic operations?
auto OrderingAddrSpace =
getFenceAddrSpaceMMRA(*MI, MOI.getOrderingAddrSpace());
const SIAtomicAddrSpace OrderingAddrSpace = MOI.getOrderingAddrSpace();

if (MOI.isAtomic()) {
const AtomicOrdering Order = MOI.getOrdering();
Expand Down
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