emit gc_state_switching

Author: vchuravy

src/llvm-late-gc-lowering.cpp

@@ -2485,8 +2485,24 @@ bool LateLowerGCFrame::CleanupIR(Function &F, State *S, bool *CFGModified) {
                 CI->replaceAllUsesWith(NewCall);
                 UpdatePtrNumbering(CI, NewCall, S);
             } else {
-                if (CI->getFnAttr("julia.gc_safe").isValid())
-                    dbgs() << "Found julia.gc_safe attribute on" << *CI;
+                if (CI->getFnAttr("julia.gc_safe").isValid()) {
+                    // Insert the operations to switch to gc_safe if necessary.
+                    IRBuilder<> builder(CI);
+                    Value *pgcstack = getPGCstack(F);
+                    assert(pgcstack);
+                    Value *ptls = get_current_ptls_from_task(builder, T_size, get_current_task_from_pgcstack(builder, T_size, pgcstack), tbaa_gcframe);
+                    Value *last_gc_state = emit_gc_safe_enter(builder, T_size, ptls, false);
+                    builder.SetInsertPoint(CI->getNextNode());
+                    // Can't use `emit_gc_safe_exit` since that wan'ts to emit some branches...
+                    // Value *old_state = builder.getInt8(JL_GC_STATE_SAFE);
+                    llvm::Value *ptls_i8 = emit_bitcast_with_builder(builder, ptls, builder.getInt8PtrTy());
+                    Constant *offset = ConstantInt::getSigned(builder.getInt32Ty(), offsetof(jl_tls_states_t, gc_state));
+                    Value *gc_state = builder.CreateInBoundsGEP(builder.getInt8Ty(), ptls_i8, ArrayRef<Value*>(offset), "gc_state");
+                    builder.CreateAlignedStore(last_gc_state, gc_state, Align(sizeof(void*)))->setOrdering(AtomicOrdering::Release);
+                    MDNode *tbaa = get_tbaa_const(builder.getContext());
+                    // unconditional safepoint due to branches
+                    emit_gc_safepoint(builder, T_size, ptls, tbaa, false);
+                }
                 if (CI->arg_size() == CI->getNumOperands()) {
                     /* No operand bundle to lower */
                     ++it;