bridge: mark write barrier functions GC leaf
Set "gc-leaf-function" attribute for the write barrier
functions. The backend understands this attribute and does not
treats the call sites as statepoints.
(llvm/lib/Transforms/Utils/Local.cpp, callsGCLeafFunction)
This makes the write barriers cheaper (avoid spillings), and
also makes it easier to remove write barriers for stack writes
(not in this CL).
Change-Id: Id5b97275b99c8717d3b9c095231ee0f6e09fe00c
Reviewed-on: https://go-review.googlesource.com/c/156558
Reviewed-by: Than McIntosh <thanm@google.com>
diff --git a/bridge/go-llvm.cpp b/bridge/go-llvm.cpp
index 41eaa0c..963c042 100644
--- a/bridge/go-llvm.cpp
+++ b/bridge/go-llvm.cpp
@@ -2533,6 +2533,25 @@
return errorFunction_.get();
}
+// This is a list of functions the call sites of which are not
+// GC statepoints.
+//
+// Keep this sync with the runtime and the frontend.
+static std::string gcleaffuncs[] = {
+ "runtime.gcWriteBarrier",
+ "runtime.typedmemmove",
+};
+
+static bool isGCLeaf(std::string name)
+{
+
+ for (auto f : gcleaffuncs)
+ if (name == f)
+ return true;
+ return false;
+
+}
+
// Declare or define a new function.
Bfunction *Llvm_backend::function(Btype *fntype, const std::string &name,
@@ -2616,6 +2635,10 @@
fcn->addFnAttr("target-cpu", targetCpuAttr_);
fcn->addFnAttr("target-features", targetFeaturesAttr_);
+ // attribute for GC leaf function (i.e. not a statepoint)
+ if (isGCLeaf(fns))
+ fcn->addFnAttr("gc-leaf-function");
+
fcnValue = fcn;
// Fix up references to declaration of old type.
