Attempt atomic legalization

Author: vchuravy

atomics.jl

@@ -0,0 +1,64 @@
+using GPUCompiler
+using LLVM
+
+function initialize()
+    if !GPUCompiler.__llvm_initialized[]
+        InitializeAllTargets()
+        InitializeAllTargetInfos()
+        InitializeAllAsmPrinters()
+        InitializeAllAsmParsers()
+        InitializeAllTargetMCs()
+        GPUCompiler.__llvm_initialized[] = true
+    end
+end
+
+# include all helpers
+include(joinpath("test", "helpers", "runtime.jl"))
+include(joinpath("test", "helpers", "ptx.jl"))
+
+job, _ = PTX.create_job(identity, (Int,))
+
+includet("src/atomic_legalization.jl")
+
+# mod = """
+# define void @test(ptr %a) nounwind {
+#   %1 = load atomic i128, ptr %a seq_cst, align 16
+#   store atomic i128 %1, ptr %a seq_cst, align 16
+#   ret void
+# }
+# """
+# => __sync_val_compare_and_swap_16
+
+
+# mod = """
+# define void @test(ptr %a) nounwind {
+#   %1 = load atomic i8, ptr %a seq_cst, align 16
+#   store atomic i8 %1, ptr %a seq_cst, align 16
+#   ret void
+# }
+# """
+
+# Cannot select: 0x67a0660: ch = AtomicStore<(store seq_cst (s8) into %ir.a, align 16)> 0x67a05f0:1, 0x67a0580, 0x67a05f0
+#   0x67a0580: i64,ch = load<(dereferenceable invariant load (s64) from `ptr addrspace(101) null`, addrspace 101)> 0x7125d30, TargetExternalSymbol:i64'test_param_0', undef:i64
+#     0x67a0200: i64 = TargetExternalSymbol'test_param_0'
+#     0x67a02e0: i64 = undef
+#   0x67a05f0: i16,ch = AtomicLoad<(load seq_cst (s8) from %ir.a, align 16)> 0x7125d30, 0x67a0580
+#     0x67a0580: i64,ch = load<(dereferenceable invariant load (s64) from `ptr addrspace(101) null`, addrspace 101)> 0x7125d30, TargetExternalSymbol:i64'test_param_0', undef:i64
+#       0x67a0200: i64 = TargetExternalSymbol'test_param_0'
+#       0x67a02e0: i64 = undef
+
+mod = """
+define i8 @test(ptr %a) nounwind {
+  %1 = load atomic i8, ptr %a seq_cst, align 16
+  ret i8 %1
+}
+"""
+
+asm, meta = JuliaContext(opaque_pointers=true) do ctx
+    initialize()
+    ir = parse(LLVM.Module, mod)
+    ir = legalize_atomics!(job, ir)
+    GPUCompiler.emit_asm(job, ir, LLVM.API.LLVMAssemblyFile)
+end
+
+

src/atomic_legalization.jl

@@ -0,0 +1,34 @@
+# in bytes
+function smallest_atomic_size(job)
+    return 4
+end
+
+# 1. Legalize sizes
+# 2. Legalize ordering through fences
+# 3. Legalize operations through cmpswp
+
+function legalize_atomics!(job, ir)
+    dl = datalayout(ir)
+    for f in functions(ir), bb in blocks(f), inst in instructions(bb)
+        if inst isa LLVM.LoadInst && is_atomic(inst)
+            typ = value_type(inst)
+            if sizeof(dl, typ) < smallest_atomic_size(job)
+                # Replace with a larger atomic type
+                @dispose builder = IRBuilder() begin
+                    position!(builder, inst)
+                    ptr = only(operands(inst))
+                    load = load!(builder, LLVM.IntType(smallest_atomic_size(job) * 8), ptr)
+                    # TODO: alignment, ordering, etc.
+                    # TODO: Handle floats and other types appropriately
+                    # TODO: Do we need to shift the loaded value?
+                    new_inst = trunc!(builder, load, typ)
+
+                    replace_uses!(inst, new_inst)
+                    erase!(inst)
+                end
+            end
+        elseif inst isa LLVM.StoreInst && is_atomic(inst)
+        end
+    end
+    return ir
+end