diff --git a/src/alloc.c b/src/alloc.c
index b3cfdc2003ceb..dd431d0e04a01 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -805,7 +805,6 @@ void jl_init_box_caches(void)
     }
 }
 
-#ifdef JL_GC_MARKSWEEP
 void jl_mark_box_caches(void)
 {
     int64_t i;
@@ -824,7 +823,6 @@ void jl_mark_box_caches(void)
         jl_gc_setmark(boxed_gensym_cache[i]);
     }
 }
-#endif
 
 jl_value_t *jl_box_bool(int8_t x)
 {
diff --git a/src/ast.c b/src/ast.c
index 4bee7e9f8a02d..26f0df1d6402e 100644
--- a/src/ast.c
+++ b/src/ast.c
@@ -197,9 +197,7 @@ static jl_value_t *full_list_of_lists(value_t e, int expronly)
 
 static jl_value_t *scm_to_julia(value_t e, int expronly)
 {
-#ifdef JL_GC_MARKSWEEP
     int en = jl_gc_enable(0);
-#endif
     jl_value_t *v;
     JL_TRY {
         v = scm_to_julia_(e, expronly);
@@ -210,9 +208,7 @@ static jl_value_t *scm_to_julia(value_t e, int expronly)
         jl_cellset(ex->args, 0, jl_cstr_to_string("invalid AST"));
         v = (jl_value_t*)ex;
     }
-#ifdef JL_GC_MARKSWEEP
     jl_gc_enable(en);
-#endif
     return v;
 }
 
diff --git a/src/builtins.c b/src/builtins.c
index 5d18d930926df..6fb28367656d7 100644
--- a/src/builtins.c
+++ b/src/builtins.c
@@ -188,9 +188,7 @@ void jl_enter_handler(jl_handler_t *eh)
 {
     JL_SIGATOMIC_BEGIN();
     eh->prev = jl_current_task->eh;
-#ifdef JL_GC_MARKSWEEP
     eh->gcstack = jl_pgcstack;
-#endif
     jl_current_task->eh = eh;
     // TODO: this should really go after setjmp(). see comment in
     // ctx_switch in task.c.
diff --git a/src/ccall.cpp b/src/ccall.cpp
index f3834c2e955f7..00c36f782cffe 100644
--- a/src/ccall.cpp
+++ b/src/ccall.cpp
@@ -715,12 +715,10 @@ static Value *emit_llvmcall(jl_value_t **args, size_t nargs, jl_codectx_t *ctx)
             }
         }
 
-#ifdef JL_GC_MARKSWEEP
         // make sure args are rooted
         if (t == jl_pvalue_llvmt && (needroot || might_need_root(argi))) {
             make_gcroot(arg, ctx);
         }
-#endif
         Value *v = julia_to_native(t, tti, arg, expr_type(argi, ctx), false, false, false, false, false, i, ctx, NULL);
         bool issigned = jl_signed_type && jl_subtype(tti, (jl_value_t*)jl_signed_type, 0);
         argvals[i] = llvm_type_rewrite(v, t, t, false, false, issigned, ctx);
@@ -1298,12 +1296,10 @@ static Value *emit_ccall(jl_value_t **args, size_t nargs, jl_codectx_t *ctx)
             }
         }
 
-#ifdef JL_GC_MARKSWEEP
         // make sure args are rooted
         if (largty == jl_pvalue_llvmt && (needroot || might_need_root(argi))) {
             make_gcroot(arg, ctx);
         }
-#endif
 
         bool nSR=false;
         bool issigned = jl_signed_type && jl_subtype(jargty, (jl_value_t*)jl_signed_type, 0);
diff --git a/src/cgutils.cpp b/src/cgutils.cpp
index 769404bc86821..f380ab0c10087 100644
--- a/src/cgutils.cpp
+++ b/src/cgutils.cpp
@@ -1874,7 +1874,6 @@ static Value* emit_allocobj(size_t static_size)
 // if ptr is NULL this emits a write barrier _back_
 static void emit_write_barrier(jl_codectx_t* ctx, Value *parent, Value *ptr)
 {
-#ifdef JL_GC_MARKSWEEP
     Value* parenttag = builder.CreateBitCast(emit_typeptr_addr(parent), T_psize);
     Value* parent_type = builder.CreateLoad(parenttag);
     Value* parent_mark_bits = builder.CreateAnd(parent_type, 1);
@@ -1897,12 +1896,10 @@ static void emit_write_barrier(jl_codectx_t* ctx, Value *parent, Value *ptr)
     builder.CreateBr(cont);
     ctx->f->getBasicBlockList().push_back(cont);
     builder.SetInsertPoint(cont);
-#endif
 }
 
 static void emit_checked_write_barrier(jl_codectx_t *ctx, Value *parent, Value *ptr)
 {
-#ifdef JL_GC_MARKSWEEP
     BasicBlock *cont;
     Value *not_null = builder.CreateICmpNE(ptr, V_null);
     BasicBlock *if_not_null = BasicBlock::Create(getGlobalContext(), "wb_not_null", ctx->f);
@@ -1913,7 +1910,6 @@ static void emit_checked_write_barrier(jl_codectx_t *ctx, Value *parent, Value *
     builder.CreateBr(cont);
     ctx->f->getBasicBlockList().push_back(cont);
     builder.SetInsertPoint(cont);
-#endif
 }
 
 static Value *emit_setfield(jl_datatype_t *sty, Value *strct, size_t idx0,
diff --git a/src/codegen.cpp b/src/codegen.cpp
index 5af7427cb35ae..c04fa3273a7c6 100644
--- a/src/codegen.cpp
+++ b/src/codegen.cpp
@@ -261,9 +261,7 @@ static GlobalVariable *jlemptytuple_var;
 #if JL_NEED_FLOATTEMP_VAR
 static GlobalVariable *jlfloattemp_var;
 #endif
-#ifdef JL_GC_MARKSWEEP
 static GlobalVariable *jlpgcstack_var;
-#endif
 static GlobalVariable *jlexc_var;
 static GlobalVariable *jldiverr_var;
 static GlobalVariable *jlundeferr_var;
@@ -334,10 +332,8 @@ static Function *box8_func;
 static Function *box16_func;
 static Function *box32_func;
 static Function *box64_func;
-#ifdef JL_GC_MARKSWEEP
 static Function *wbfunc;
 static Function *queuerootfun;
-#endif
 static Function *expect_func;
 static Function *jldlsym_func;
 static Function *jlnewbits_func;
@@ -540,11 +536,9 @@ struct jl_gcinfo_t {
     int argDepth;
     int maxDepth;
     int argSpaceOffs;
-#ifdef JL_GC_MARKSWEEP
     Instruction *gcframe;
     Instruction *argSpaceInits;
     StoreInst *storeFrameSize;
-#endif
     BasicBlock::iterator first_gcframe_inst;
     BasicBlock::iterator last_gcframe_inst;
     std::vector<Instruction*> gc_frame_pops;
@@ -2696,10 +2690,8 @@ static Value *emit_call(jl_value_t **args, size_t arglen, jl_codectx_t *ctx, jl_
             }
             if (theFptr == NULL) {
                 Value *theFunc = emit_expr(args[0], ctx);
-#ifdef JL_GC_MARKSWEEP
                 if (!headIsGlobal && (jl_is_expr(a0) || jl_is_lambda_info(a0)))
                     make_gcroot(boxed(theFunc,ctx), ctx);
-#endif
                 // extract pieces of the function object
                 // TODO: try extractvalue instead
                 theFptr = emit_nthptr_recast(theFunc, (ssize_t)(offsetof(jl_function_t,fptr)/sizeof(void*)), tbaa_func, jl_pfptr_llvmt);
@@ -3579,7 +3571,6 @@ static void allocate_gc_frame(size_t n_roots, BasicBlock *b0, jl_codectx_t *ctx)
     gc->argDepth = 0;
     gc->maxDepth = 0;
 
-#ifdef JL_GC_MARKSWEEP
     // allocate gc frame
     // gc->gcframe is assumed to be the first instruction creating the gc frame
     // in finalize_gc_frame.
@@ -3595,14 +3586,6 @@ static void allocate_gc_frame(size_t n_roots, BasicBlock *b0, jl_codectx_t *ctx)
                         builder.CreateBitCast(builder.CreateConstGEP1_32(gc->gcframe, 1), PointerType::get(jl_ppvalue_llvmt,0)));
     Instruction *linst = builder.CreateStore(gc->gcframe, prepare_global(jlpgcstack_var), false);
     gc->argSpaceInits = &b0->back();
-#else
-    // gc->gcframe is assumed to be the first instruction creating the gc frame
-    // in finalize_gc_frame
-    gc->argTemp = builder.CreateAlloca(jl_pvalue_llvmt,
-                                       ConstantInt::get(T_int32, n_roots));
-    gc->first_gcframe_inst = BasicBlock::iterator(gc->argTemp);
-    Instruction *linst = gc->argTemp;
-#endif
     // initialize local variable stack roots to null
     for(size_t i=0; i < (size_t)gc->argSpaceOffs; i++) {
         Value *varSlot = emit_local_slot(i, ctx);
@@ -3656,7 +3639,6 @@ static void clear_gc_frame(jl_gcinfo_t *gc)
 static void finalize_gc_frame(jl_codectx_t *ctx)
 {
     jl_gcinfo_t *gc = &ctx->gc;
-#ifdef JL_GC_MARKSWEEP
     if (gc->argSpaceOffs + gc->maxDepth == 0) {
         // 0 roots; remove gc frame entirely
         clear_gc_frame(gc);
@@ -3691,23 +3673,11 @@ static void finalize_gc_frame(jl_codectx_t *ctx)
             instList.insertAfter(argTempi, after);
         }
     }
-#else
-    if (gc->maxDepth != 0) {
-        BasicBlock::iterator bbi(gc->argTemp);
-        AllocaInst *newgcframe =
-            new AllocaInst(jl_pvalue_llvmt,
-                           ConstantInt::get(T_int32, (gc->argSpaceOffs +
-                                                      gc->maxDepth)));
-        ReplaceInstWithInst(gc->argTemp->getParent()->getInstList(), bbi,
-                            newgcframe);
-    }
-#endif
 }
 
 static void
 emit_gcpop(jl_codectx_t *ctx)
 {
-#ifdef JL_GC_MARKSWEEP
     // finalize_gc_frame assumes each frame pop takes 4 instructions.
     Instruction *gcpop =
         (Instruction*)builder.CreateConstGEP1_32(ctx->gc.gcframe, 1);
@@ -3715,9 +3685,6 @@ emit_gcpop(jl_codectx_t *ctx)
     builder.CreateStore(builder.CreateBitCast(builder.CreateLoad(gcpop, false),
                                               jl_ppvalue_llvmt),
                         prepare_global(jlpgcstack_var));
-#else
-    (void)ctx;
-#endif
 }
 
 static Function *gen_cfun_wrapper(jl_function_t *ff, jl_value_t *jlrettype, jl_tupletype_t *argt, int64_t isref)
@@ -5129,13 +5096,11 @@ static void init_julia_llvm_env(Module *m)
                            "jl_array_t");
     jl_parray_llvmt = PointerType::get(jl_array_llvmt,0);
 
-#ifdef JL_GC_MARKSWEEP
     jlpgcstack_var =
         new GlobalVariable(*m, jl_ppvalue_llvmt,
                            false, GlobalVariable::ExternalLinkage,
                            NULL, "jl_pgcstack");
     add_named_global(jlpgcstack_var, (void*)&jl_pgcstack);
-#endif
 
     global_to_llvm("__stack_chk_guard", (void*)&__stack_chk_guard, m);
     Function *jl__stack_chk_fail =
@@ -5356,7 +5321,6 @@ static void init_julia_llvm_env(Module *m)
     jlgetfield_func = builtin_func_map[jl_f_get_field];
     jlapplygeneric_func = jlcall_func_to_llvm("jl_apply_generic", (void*)&jl_apply_generic, m);
 
-#ifdef JL_GC_MARKSWEEP
     queuerootfun = Function::Create(FunctionType::get(T_void, args_1ptr, false),
                                     Function::ExternalLinkage,
                                     "jl_gc_queue_root", m);
@@ -5369,7 +5333,6 @@ static void init_julia_llvm_env(Module *m)
                               Function::ExternalLinkage,
                               "jl_gc_wb_slow", m);
     add_named_global(wbfunc, (void*)&jl_gc_wb_slow);
-#endif
 
     std::vector<Type *> exp_args(0);
     exp_args.push_back(T_int1);
diff --git a/src/dump.c b/src/dump.c
index cb778e2ce8d71..be77ebfd8fc35 100644
--- a/src/dump.c
+++ b/src/dump.c
@@ -1526,9 +1526,7 @@ DLLEXPORT void jl_preload_sysimg_so(const char *fname)
 
 void jl_restore_system_image_from_stream(ios_t *f)
 {
-#ifdef JL_GC_MARKSWEEP
     int en = jl_gc_enable(0);
-#endif
     DUMP_MODES last_mode = mode;
     mode = MODE_SYSTEM_IMAGE;
     arraylist_new(&backref_list, 250000);
@@ -1594,9 +1592,7 @@ void jl_restore_system_image_from_stream(ios_t *f)
     //jl_printf(JL_STDERR, "backref_list.len = %d\n", backref_list.len);
     arraylist_free(&backref_list);
 
-#ifdef JL_GC_MARKSWEEP
     jl_gc_enable(en);
-#endif
     mode = last_mode;
     jl_update_all_fptrs();
 }
diff --git a/src/gc.c b/src/gc.c
index 9cb9a904af706..950e2c2093d9e 100644
--- a/src/gc.c
+++ b/src/gc.c
@@ -188,8 +188,6 @@ void jl_finalize(jl_value_t *o)
     (void)finalize_object(o);
 }
 
-#ifdef JL_GC_MARKSWEEP
-
 typedef struct _buff_t {
     union {
         uintptr_t header;
@@ -2680,33 +2678,6 @@ static void big_obj_stats(void)
 }
 #endif //MEMPROFILE
 
-#else //JL_GC_MARKSWEEP
-DLLEXPORT jl_value_t *jl_gc_allocobj(size_t sz)
-{
-    size_t allocsz = sz + sizeof_jl_taggedvalue_t;
-    if (allocsz < sz)  // overflow in adding offs, size was "negative"
-        jl_throw(jl_memory_exception);
-    allocd_bytes += allocsz;
-    gc_num.alloc++;
-    return jl_valueof(malloc(allocsz));
-}
-int64_t jl_gc_diff_total_bytes(void)
-{
-    return 0;
-}
-DLLEXPORT jl_weakref_t *jl_gc_new_weakref(jl_value_t *value)
-{
-    jl_weakref_t *wr = (jl_weakref_t*)jl_gc_alloc_1w();
-    jl_set_typeof(wr, jl_weakref_type);
-    wr->value = value;
-    return wr;
-}
-static inline int maybe_collect(void)
-{
-    return 0;
-}
-#endif //JL_GC_MARKSWEEP
-
 DLLEXPORT void *jl_gc_counted_malloc(size_t sz)
 {
     maybe_collect();
@@ -2762,14 +2733,11 @@ DLLEXPORT void *jl_gc_managed_realloc(void *d, size_t sz, size_t oldsz, int isal
     if (allocsz < sz)  // overflow in adding offs, size was "negative"
         jl_throw(jl_memory_exception);
 
-#ifdef JL_GC_MARKSWEEP
     if (gc_bits(jl_astaggedvalue(owner)) == GC_MARKED) {
         perm_scanned_bytes += allocsz - oldsz;
         live_bytes += allocsz - oldsz;
     }
-    else
-#endif
-    if (allocsz < oldsz)
+    else if (allocsz < oldsz)
         freed_bytes += (oldsz - allocsz);
     else
         allocd_bytes += (allocsz - oldsz);
diff --git a/src/init.c b/src/init.c
index 4369a0e3b8188..89387c50c9875 100644
--- a/src/init.c
+++ b/src/init.c
@@ -544,7 +544,7 @@ static struct uv_shutdown_queue_item *next_shutdown_queue_item(struct uv_shutdow
 
 DLLEXPORT void jl_atexit_hook()
 {
-#if defined(JL_GC_MARKSWEEP) && defined(GC_FINAL_STATS)
+#if defined(GC_FINAL_STATS)
     jl_print_gc_stats(JL_STDERR);
 #endif
     if (jl_options.code_coverage)
@@ -1067,10 +1067,8 @@ void _julia_init(JL_IMAGE_SEARCH rel)
     }
 #endif
 
-#ifdef JL_GC_MARKSWEEP
     jl_gc_init();
     jl_gc_enable(0);
-#endif
     jl_init_frontend();
     jl_init_types();
     jl_init_tasks();
@@ -1140,9 +1138,7 @@ void _julia_init(JL_IMAGE_SEARCH rel)
     if (jl_options.handle_signals == JL_OPTIONS_HANDLE_SIGNALS_ON)
         jl_install_default_signal_handlers();
 
-#ifdef JL_GC_MARKSWEEP
     jl_gc_enable(1);
-#endif
 
     if (jl_options.image_file)
         jl_init_restored_modules();
diff --git a/src/julia.h b/src/julia.h
index d1881951327a8..e6ec13b47d92f 100644
--- a/src/julia.h
+++ b/src/julia.h
@@ -492,7 +492,6 @@ extern jl_sym_t *arrow_sym; extern jl_sym_t *inert_sym;
 
 // gc -------------------------------------------------------------------------
 
-#ifdef JL_GC_MARKSWEEP
 typedef struct _jl_gcframe_t {
     size_t nroots;
     struct _jl_gcframe_t *prev;
@@ -608,44 +607,6 @@ static inline void jl_gc_wb_back(void *ptr) // ptr isa jl_value_t*
     }
 }
 
-#else // No Garbage Collection
-
-#define JL_GC_PUSH(...) ;
-#define JL_GC_PUSH1(...) ;
-#define JL_GC_PUSH2(...) ;
-#define JL_GC_PUSH3(...) ;
-#define JL_GC_PUSH4(...) ;
-#define JL_GC_PUSH5(...) ;
-#define JL_GC_PUSHARGS(rts_var,n) rts_var = ((jl_value_t**)alloca((n)*sizeof(jl_value_t*)));
-#define JL_GC_POP()
-
-#define jl_gc_preserve(v) ((void)(v))
-#define jl_gc_unpreserve()
-#define jl_gc_n_preserved_values() (0)
-
-#define allocb(nb)    malloc(nb)
-DLLEXPORT jl_value_t *jl_gc_allocobj(size_t sz);
-STATIC_INLINE jl_value_t *jl_gc_alloc_1w() { return jl_gc_allocobj(1*sizeof(void*)); }
-STATIC_INLINE jl_value_t *jl_gc_alloc_2w() { return jl_gc_allocobj(2*sizeof(void*)); }
-STATIC_INLINE jl_value_t *jl_gc_alloc_3w() { return jl_gc_allocobj(3*sizeof(void*)); }
-
-DLLEXPORT void jl_gc_add_finalizer(jl_value_t *v, jl_function_t *f);
-
-int64_t jl_gc_diff_total_bytes(void);
-#define jl_gc_sync_total_bytes()
-#define jl_gc_collect(arg);
-#define jl_gc_enable(on) (0)
-#define jl_gc_is_enabled() (0)
-#define jl_gc_track_malloced_array(a)
-#define jl_gc_count_allocd(sz)
-
-#define jl_gc_wb_binding(bnd, val)
-#define jl_gc_wb(parent, ptr)
-#define jl_gc_wb_buf(parent, bufptr)
-#define jl_gc_wb_back(ptr)
-
-#endif
-
 DLLEXPORT void *jl_gc_managed_malloc(size_t sz);
 DLLEXPORT void *jl_gc_managed_realloc(void *d, size_t sz, size_t oldsz, int isaligned, jl_value_t* owner);
 
@@ -1338,9 +1299,7 @@ void jl_install_default_signal_handlers(void);
 // info describing an exception handler
 typedef struct _jl_handler_t {
     jl_jmp_buf eh_ctx;
-#ifdef JL_GC_MARKSWEEP
     jl_gcframe_t *gcstack;
-#endif
     struct _jl_handler_t *prev;
 } jl_handler_t;
 
@@ -1365,10 +1324,8 @@ typedef struct _jl_task_t {
 
     // current exception handler
     jl_handler_t *eh;
-#ifdef JL_GC_MARKSWEEP
     // saved gc stack top for context switches
     jl_gcframe_t *gcstack;
-#endif
     // current module, or NULL if this task has not set one
     jl_module_t *current_module;
 } jl_task_t;
@@ -1388,9 +1345,7 @@ STATIC_INLINE void jl_eh_restore_state(jl_handler_t *eh)
 {
     JL_SIGATOMIC_BEGIN();
     jl_current_task->eh = eh->prev;
-#ifdef JL_GC_MARKSWEEP
     jl_pgcstack = eh->gcstack;
-#endif
     JL_SIGATOMIC_END();
 }
 
@@ -1522,7 +1477,7 @@ DLLEXPORT size_t jl_static_show(JL_STREAM *out, jl_value_t *v);
 DLLEXPORT size_t jl_static_show_func_sig(JL_STREAM *s, jl_value_t *type);
 DLLEXPORT void jlbacktrace(void);
 
-#if defined(GC_FINAL_STATS) && defined(JL_GC_MARKSWEEP)
+#if defined(GC_FINAL_STATS)
 void jl_print_gc_stats(JL_STREAM *s);
 #endif
 
diff --git a/src/options.h b/src/options.h
index 43aba33de8103..23540aee47121 100644
--- a/src/options.h
+++ b/src/options.h
@@ -35,9 +35,6 @@
 
 // GC options -----------------------------------------------------------------
 
-// only one GC is supported at this time
-#define JL_GC_MARKSWEEP
-
 // debugging options
 
 // with MEMDEBUG, every object is allocated explicitly with malloc, and
diff --git a/src/task.c b/src/task.c
index 3ca050988ac84..88a740e407924 100644
--- a/src/task.c
+++ b/src/task.c
@@ -147,9 +147,7 @@ jl_datatype_t *jl_task_type;
 DLLEXPORT JL_THREAD jl_task_t * volatile jl_current_task;
 JL_THREAD jl_task_t *jl_root_task;
 DLLEXPORT JL_THREAD jl_value_t *jl_exception_in_transit;
-#ifdef JL_GC_MARKSWEEP
 DLLEXPORT JL_THREAD jl_gcframe_t *jl_pgcstack = NULL;
-#endif
 
 #ifdef COPY_STACKS
 static JL_THREAD jl_jmp_buf * volatile jl_jmp_target;
@@ -302,10 +300,8 @@ static void ctx_switch(jl_task_t *t, jl_jmp_buf *where)
 #endif
 
         // set up global state for new task
-#ifdef JL_GC_MARKSWEEP
         jl_current_task->gcstack = jl_pgcstack;
         jl_pgcstack = t->gcstack;
-#endif
 
         // restore task's current module, looking at parent tasks
         // if it hasn't set one.
@@ -843,9 +839,7 @@ DLLEXPORT jl_task_t *jl_new_task(jl_function_t *start, size_t ssize)
     t->exception = jl_nothing;
     // there is no active exception handler available on this stack yet
     t->eh = NULL;
-#ifdef JL_GC_MARKSWEEP
     t->gcstack = NULL;
-#endif
     t->stkbuf = NULL;
 
 #ifdef COPY_STACKS
@@ -945,9 +939,7 @@ void jl_init_root_task(void *stack, size_t ssize)
     jl_current_task->donenotify = NULL;
     jl_current_task->exception = NULL;
     jl_current_task->eh = NULL;
-#ifdef JL_GC_MARKSWEEP
     jl_current_task->gcstack = NULL;
-#endif
 
     jl_root_task = jl_current_task;