Don't DCE the exception flag.

This improves output while running under CUDA memcheck, avoiding
plenty API failures when not finding the global.

src/compiler/exceptions.jl

@@ -18,12 +18,19 @@ end
 # since we don't actually support globals, access to this variable is done by calling the
 # julia_exception_flag function (lowered here to actual accesses of the variable)
 function emit_exception_flag!(mod::LLVM.Module)
- # add the global variable
- T_ptr = convert(LLVMType, Ptr{Cvoid})
- gv = GlobalVariable(mod, T_ptr, "exception_flag")
- initializer!(gv, LLVM.ConstantInt(T_ptr, 0))
- linkage!(gv, LLVM.API.LLVMWeakAnyLinkage)
- extinit!(gv, true)
+ # add the global variable if it doesn't exist yet (might have come from the runtime)
+ # TODO: get!
+ if !haskey(globals(mod), "exception_flag")
+ T_ptr = convert(LLVMType, Ptr{Cvoid})
+ gv = GlobalVariable(mod, T_ptr, "exception_flag")
+ initializer!(gv, LLVM.ConstantInt(T_ptr, 0))
+ linkage!(gv, LLVM.API.LLVMWeakAnyLinkage)
+ extinit!(gv, true)
+
+ set_used!(mod, gv)
+ else
+ gv = globals(mod)["exception_flag"]
+ end
 
  # lower uses of the getter
  if haskey(functions(mod), "julia_exception_flag")
@@ -58,15 +65,21 @@ const exception_flags = Dict{CuContext, Mem.HostBuffer}()
 #
 # also see compiler/irgen.jl::emit_exception_flag!
 function create_exceptions!(mod::CuModule)
- ctx = mod.ctx
- try
+ if VERSION >= v"1.5" && !(v"1.6-" <= VERSION < v"1.6.0-DEV.90")
  flag_ptr = CuGlobal{Ptr{Cvoid}}(mod, "exception_flag")
- exception_flag = get!(exception_flags, ctx, Mem.alloc(Mem.Host, sizeof(Int),
-   Mem.HOSTALLOC_DEVICEMAP))
+ exception_flag = get!(exception_flags, mod.ctx,
+ Mem.alloc(Mem.Host, sizeof(Int), Mem.HOSTALLOC_DEVICEMAP))
  flag_ptr[] = reinterpret(Ptr{Cvoid}, convert(CuPtr{Cvoid}, exception_flag))
- catch err
- # modules that do not throw exceptions will not contain the indicator flag
- (isa(err, CuError) && err.code == ERROR_NOT_FOUND) || rethrow()
+ else
+ ctx = mod.ctx
+ try
+ flag_ptr = CuGlobal{Ptr{Cvoid}}(mod, "exception_flag")
+ exception_flag = get!(exception_flags, ctx, Mem.alloc(Mem.Host, sizeof(Int),
+ Mem.HOSTALLOC_DEVICEMAP))
+ flag_ptr[] = reinterpret(Ptr{Cvoid}, convert(CuPtr{Cvoid}, exception_flag))
+ catch err
+ (isa(err, CuError) && err.code == ERROR_NOT_FOUND) || rethrow()
+ end
  end
 
  return