Implement NVVMReflect in Julia. (#280)

Author: maleadt

src/ptx.jl

@@ -150,6 +150,9 @@ function optimize_module!(@nospecialize(job::CompilerJob{PTXCompilerTarget}),
         add_library_info!(pm, triple(mod))
         add_transform_info!(pm, tm)
 
+        # TODO: need to run this earlier; optimize_module! is called after addOptimizationPasses!
+        add!(pm, FunctionPass("NVVMReflect", nvvm_reflect!))
+
         # needed by GemmKernels.jl-like code
         speculative_execution_if_has_branch_divergence!(pm)
 
@@ -392,3 +395,83 @@ function hide_trap!(mod::LLVM.Module)
     end
     return changed
 end
+
+# Replace occurrences of __nvvm_reflect("foo") and llvm.nvvm.reflect with an integer.
+#
+# NOTE: this is the same as LLVM's NVVMReflect pass, which we cannot use because it is
+#       not exported. It is meant to be added to a pass pipeline automatically, by
+#       calling adjustPassManager, but we don't use a PassManagerBuilder so cannot do so.
+const NVVM_REFLECT_FUNCTION = "__nvvm_reflect"
+function nvvm_reflect!(fun::LLVM.Function)
+    job = current_job::CompilerJob
+    mod = LLVM.parent(fun)
+    ctx = context(fun)
+    changed = false
+    @timeit_debug to "nvvmreflect" begin
+
+    # find and sanity check the nnvm-reflect function
+    # TODO: also handle the llvm.nvvm.reflect intrinsic
+    haskey(LLVM.functions(mod), NVVM_REFLECT_FUNCTION) || return false
+    reflect_function = LLVM.functions(mod)[NVVM_REFLECT_FUNCTION]
+    isdeclaration(reflect_function) || error("_reflect function should not have a body")
+    reflect_typ = return_type(eltype(llvmtype(reflect_function)))
+    isa(reflect_typ, LLVM.IntegerType) || error("_reflect's return type should be integer")
+
+    to_remove = []
+    for use in uses(reflect_function)
+        call = user(use)
+        isa(call, LLVM.CallInst) || continue
+        length(operands(call)) == 2 || error("Wrong number of operands to __nvvm_reflect function")
+
+        # decode the string argument
+        str = operands(call)[1]
+        isa(str, LLVM.ConstantExpr) || error("Format of __nvvm__reflect function not recognized")
+        sym = operands(str)[1]
+        isa(sym, LLVM.GlobalVariable) || error("Format of __nvvm__reflect function not recognized")
+        sym_op = operands(sym)[1]
+        isa(sym_op, LLVM.ConstantArray) || error("Format of __nvvm__reflect function not recognized")
+        chars = convert.(Ref(UInt8), collect(sym_op))
+        reflect_arg = String(chars[1:end-1])
+
+        # handle possible cases
+        # XXX: put some of these property in the compiler job?
+        #      and/or first set the "nvvm-reflect-*" module flag like Clang does?
+        fast_math = Base.JLOptions().fast_math == 1
+        # NOTE: we follow nvcc's --use_fast_math
+        reflect_val = if reflect_arg == "__CUDA_FTZ"
+            # single-precision denormals support
+            ConstantInt(reflect_typ, fast_math ? 1 : 0)
+        elseif reflect_arg == "__CUDA_PREC_DIV"
+            # single-precision floating-point division and reciprocals.
+            ConstantInt(reflect_typ, fast_math ? 0 : 1)
+        elseif reflect_arg == "__CUDA_PREC_SQRT"
+            # single-precision denormals support
+            ConstantInt(reflect_typ, fast_math ? 0 : 1)
+        elseif reflect_arg == "__CUDA_FMAD"
+            # contraction of floating-point multiplies and adds/subtracts into
+            # floating-point multiply-add operations (FMAD, FFMA, or DFMA)
+            ConstantInt(reflect_typ, fast_math ? 1 : 0)
+        elseif reflect_arg == "__CUDA_ARCH"
+            ConstantInt(reflect_typ, job.target.cap.major*100 + job.target.cap.minor*10)
+        else
+            @warn "Unknown __nvvm_reflect argument: $reflect_arg. Please file an issue."
+        end
+
+        replace_uses!(call, reflect_val)
+        push!(to_remove, call)
+    end
+
+    # remove the calls to the function
+    for val in to_remove
+        @assert isempty(uses(val))
+        unsafe_delete!(LLVM.parent(val), val)
+    end
+
+    # maybe also delete the function
+    if isempty(uses(reflect_function))
+        unsafe_delete!(mod, reflect_function)
+    end
+
+    end
+    return changed
+end