CSE: cse builtin "once" calls

`builtin "once"` calls are a result of inlining global accessors

Author: eeckstein

lib/SILOptimizer/Transforms/CSE.cpp

@@ -1187,11 +1187,17 @@ bool CSE::canHandle(SILInstruction *Inst) {
     return false;
   }
   if (auto *BI = dyn_cast<BuiltinInst>(Inst)) {
-    // Although the onFastPath builtin has no side-effects we don't want to
-    // (re-)move it.
-    if (BI->getBuiltinInfo().ID == BuiltinValueKind::OnFastPath)
+    switch (BI->getBuiltinInfo().ID) {
+    case BuiltinValueKind::OnFastPath:
+      // Although the onFastPath builtin has no side-effects we don't want to
+      // (re-)move it.
       return false;
-    return !BI->mayReadOrWriteMemory();
+    case BuiltinValueKind::Once:
+    case BuiltinValueKind::OnceWithContext:
+      return true;
+    default:
+      return !BI->mayReadOrWriteMemory();
+    }
   }
   if (auto *EMI = dyn_cast<ExistentialMetatypeInst>(Inst)) {
     return !EMI->getOperand()->getType().isAddress();

test/SILOptimizer/cse.sil

@@ -1411,3 +1411,40 @@ entry(%instance : $FC):
     return %retval : $()
 }
 
+sil_global private @g_token : $Builtin.Word
+sil_global private @g2_token : $Builtin.Word
+
+sil @g_init : $@convention(c) () -> ()
+
+// CHECK-LABEL: sil @cse_builtin_once :
+// CHECK:         builtin
+// CHECK-NOT:     builtin
+// CHECK:       } // end sil function 'cse_builtin_once'
+sil @cse_builtin_once : $@convention(thin) () -> () {
+bb0:
+  %1 = global_addr @g_token : $*Builtin.Word
+  %2 = address_to_pointer %1 : $*Builtin.Word to $Builtin.RawPointer
+  %3 = function_ref @g_init : $@convention(c) () -> ()
+  %4 = builtin "once"(%2 : $Builtin.RawPointer, %3 : $@convention(c) () -> ()) : $()
+  %5 = builtin "once"(%2 : $Builtin.RawPointer, %3 : $@convention(c) () -> ()) : $()
+  %r1 = tuple ()
+  return %r1 : $()
+}
+
+// CHECK-LABEL: sil @dont_cse_builtin_once_different_token :
+// CHECK:         builtin
+// CHECK:         builtin
+// CHECK:       } // end sil function 'dont_cse_builtin_once_different_token'
+sil @dont_cse_builtin_once_different_token : $@convention(thin) () -> () {
+bb0:
+  %1 = global_addr @g_token : $*Builtin.Word
+  %2 = address_to_pointer %1 : $*Builtin.Word to $Builtin.RawPointer
+  %3 = global_addr @g2_token : $*Builtin.Word
+  %4 = address_to_pointer %3 : $*Builtin.Word to $Builtin.RawPointer
+  %5 = function_ref @g_init : $@convention(c) () -> ()
+  %6 = builtin "once"(%2 : $Builtin.RawPointer, %5 : $@convention(c) () -> ()) : $()
+  %7 = builtin "once"(%4 : $Builtin.RawPointer, %5 : $@convention(c) () -> ()) : $()
+  %r1 = tuple ()
+  return %r1 : $()
+}
+