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Fix hardware FP atomics on Julia 1.13 (LLVM 20) #923

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Fix hardware FP atomics on Julia 1.13 (LLVM 20) #923

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76d1cf3
Fix atomic for 1.13
luraess May 26, 2026
a106753
Fixup
luraess May 26, 2026
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21 changes: 20 additions & 1 deletion src/compiler/codegen.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -91,6 +91,25 @@ function GPUCompiler.finish_module!(
end
end

# LLVM 20+ requires !amdgpu.no.fine.grained.memory on FP atomicrmw to emit
# native hardware atomics (e.g. global_atomic_add_f32) instead of a CAS loop.
# Mirrors Clang's setTargetAtomicMetadata; unsafe_fp_atomics is the opt-in.
if job.config.params.unsafe_fp_atomics
fp_binops = (LLVM.API.LLVMAtomicRMWBinOpFAdd, LLVM.API.LLVMAtomicRMWBinOpFSub,
LLVM.API.LLVMAtomicRMWBinOpFMax, LLVM.API.LLVMAtomicRMWBinOpFMin)
empty_md = MDNode(Metadata[])
for fn in LLVM.functions(mod), bb in LLVM.blocks(fn), inst in LLVM.instructions(bb)
inst isa LLVM.AtomicRMWInst || continue
op = LLVM.binop(inst)
op ∈ fp_binops || continue
md = LLVM.metadata(inst)
md["amdgpu.no.fine.grained.memory"] = empty_md
if op == LLVM.API.LLVMAtomicRMWBinOpFAdd && LLVM.value_type(inst) == LLVM.FloatType()
md["amdgpu.ignore.denormal.mode"] = empty_md
end
end
end

return entry
end

Expand Down Expand Up @@ -200,7 +219,7 @@ function hipcompile(@nospecialize(job::CompilerJob))
GPUCompiler.compile(:obj, job)
end

global_hostcalls = pop!(_global_hostcalls, hash(job))
global_hostcalls = pop!(_global_hostcalls, hash(job), Symbol[])
# Late global hostcalls detection.
append!(global_hostcalls, find_global_hostcalls(meta.ir))

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