Add a white list of known non-safepoint functions

These are functions we emit in codegen directly that are known to not contain any safepoint

Author: yuyichao

src/codegen.cpp

@@ -321,7 +321,7 @@ static Function *jlisa_func;
 static Function *jlsubtype_func;
 static Function *jlapplytype_func;
 static Function *setjmp_func;
-static Function *memcmp_func;
+static Function *memcmp_derived_func;
 static Function *box_int8_func;
 static Function *box_uint8_func;
 static Function *box_int16_func;
@@ -2280,7 +2280,7 @@ static Value *emit_bits_compare(jl_codectx_t &ctx, const jl_cgval_t &arg1, const
         assert(arg1.ispointer() && arg2.ispointer());
         size_t sz = jl_datatype_size(arg1.typ);
         if (sz > 512 && !((jl_datatype_t*)arg1.typ)->layout->haspadding) {
-            Value *answer = ctx.builder.CreateCall(prepare_call(memcmp_func),
+            Value *answer = ctx.builder.CreateCall(prepare_call(memcmp_derived_func),
                             {
                             data_pointer(ctx, arg1, T_pint8),
                             data_pointer(ctx, arg2, T_pint8),
@@ -6138,6 +6138,8 @@ static void init_julia_llvm_env(Module *m)
     T_void = Type::getVoidTy(jl_LLVMContext);
     T_pvoidfunc = FunctionType::get(T_void, /*isVarArg*/false)->getPointerTo();
 
+    auto T_pint8_derived = PointerType::get(T_int8, AddressSpace::Derived);
+
     // This type is used to create undef Values for use in struct declarations to skip indices
     NoopType = ArrayType::get(T_int1, 0);
 
@@ -6352,7 +6354,7 @@ static void init_julia_llvm_env(Module *m)
     add_named_global(jlvboundserror_func, &jl_bounds_error_tuple_int);
 
     std::vector<Type*> args3_uboundserror(0);
-    args3_uboundserror.push_back(PointerType::get(T_int8, AddressSpace::Derived));
+    args3_uboundserror.push_back(T_pint8_derived);
     args3_uboundserror.push_back(T_prjlvalue);
     args3_uboundserror.push_back(T_size);
     jluboundserror_func =
@@ -6379,13 +6381,13 @@ static void init_julia_llvm_env(Module *m)
     add_named_global(setjmp_func, &jl_setjmp_f);
 
     std::vector<Type*> args_memcmp(0);
-    args_memcmp.push_back(T_pint8);
-    args_memcmp.push_back(T_pint8);
+    args_memcmp.push_back(T_pint8_derived);
+    args_memcmp.push_back(T_pint8_derived);
     args_memcmp.push_back(T_size);
-    memcmp_func =
+    memcmp_derived_func =
         Function::Create(FunctionType::get(T_int32, args_memcmp, false),
                          Function::ExternalLinkage, "memcmp", m);
-    add_named_global(memcmp_func, &memcmp);
+    add_named_global(memcmp_derived_func, &memcmp);
 
     std::vector<Type*> te_args(0);
     te_args.push_back(T_pint8);

src/llvm-late-gc-lowering.cpp

@@ -729,6 +729,12 @@ State LateLowerGCFrame::LocalScan(Function &F) {
                 if (CI->canReturnTwice()) {
                     S.ReturnsTwice.push_back(CI);
                 }
+                if (auto callee = CI->getCalledFunction()) {
+                    // Known functions emitted in codegen that are not safepoints
+                    if (callee == pointer_from_objref_func || callee->getName() == "memcmp") {
+                        continue;
+                    }
+                }
                 int SafepointNumber = NoteSafepoint(S, BBS, CI);
                 BBS.HasSafepoint = true;
                 BBS.TopmostSafepoint = SafepointNumber;

test/codegen.jl

@@ -101,4 +101,37 @@ if opt_level > 0
     test_jl_dump_compiles_toplevel_thunks()
 end
 
-@test !contains(get_llvm(isequal, Tuple{Nullable{BigFloat}, Nullable{BigFloat}}), "%gcframe")
+# Make sure we will not elide the allocation
+@noinline create_ref1() = Ref(1)
+function pointer_not_safepoint()
+    a = create_ref1()
+    unsafe_store!(Ptr{Int}(pointer_from_objref(a)), 3)
+    return a[]
+end
+@test pointer_not_safepoint() == 3
+
+# The current memcmp threshold is 512bytes, make sure this struct has the same size on
+# 32bits and 64bits
+struct LargeStruct
+    x::NTuple{1024,Int8}
+    LargeStruct() = new()
+end
+
+const large_struct = LargeStruct()
+@noinline create_ref_struct() = Ref(large_struct)
+function compare_large_struct(a)
+    b = create_ref_struct()
+    if a[] === b[]
+        b[].x[1]
+    else
+        a[].x[2]
+    end
+end
+
+if opt_level > 0
+    @test !contains(get_llvm(isequal, Tuple{Nullable{BigFloat}, Nullable{BigFloat}}), "%gcframe")
+    @test !contains(get_llvm(pointer_not_safepoint, Tuple{}), "%gcframe")
+    compare_large_struct_ir = get_llvm(compare_large_struct, Tuple{typeof(create_ref_struct())})
+    @test contains(compare_large_struct_ir, "call i32 @memcmp")
+    @test !contains(compare_large_struct_ir, "%gcframe")
+end