Emit safepoints at function entry

Author: vchuravy

src/ccall.cpp

@@ -1457,10 +1457,7 @@ static jl_cgval_t emit_ccall(jl_codectx_t &ctx, jl_value_t **args, size_t nargs)
         assert(lrt == T_void);
         assert(!isVa && !llvmcall && nccallargs == 0);
         JL_GC_POP();
-        ctx.builder.CreateCall(prepare_call(gcroot_flush_func));
-        emit_signal_fence(ctx);
-        ctx.builder.CreateLoad(T_size, get_current_signal_page(ctx), true);
-        emit_signal_fence(ctx);
+        emit_safepoint(ctx);
         return ghostValue(jl_nothing_type);
     }
     else if (is_libjulia_func("jl_get_ptls_states")) {

src/cgutils.cpp

@@ -3448,6 +3448,14 @@ static Value *emit_defer_signal(jl_codectx_t &ctx)
     return ctx.builder.CreateInBoundsGEP(T_sigatomic, ptls, ArrayRef<Value*>(offset), "jl_defer_signal");
 }
 
+static void emit_safepoint(jl_codectx_t &ctx)
+{
+    ctx.builder.CreateCall(prepare_call(gcroot_flush_func));
+    emit_signal_fence(ctx);
+    ctx.builder.CreateLoad(T_size, get_current_signal_page(ctx), true);
+    emit_signal_fence(ctx);
+}
+
 #ifndef NDEBUG
 static int compare_cgparams(const jl_cgparams_t *a, const jl_cgparams_t *b)
 {

src/codegen.cpp

@@ -6892,8 +6892,10 @@ static std::pair<std::unique_ptr<Module>, jl_llvm_functions_t>
 
     Instruction &prologue_end = ctx.builder.GetInsertBlock()->back();
 
+    // step 11a. Emit the entry safepoint
+    emit_safepoint(ctx);
 
-    // step 11. Do codegen in control flow order
+    // step 11b. Do codegen in control flow order
     std::vector<int> workstack;
     std::map<int, BasicBlock*> BB;
     std::map<size_t, BasicBlock*> come_from_bb;