[PlaceSafepoints] New attributes for patchable statepoints.

Summary:
This patch teaches the PlaceSafepoints pass about two `CallSite`
function attributes:

 * "statepoint-id": if the string value of this attribute can be parsed
   as an integer, then it is propagated to the ID parameter of the
   statepoint created.

 * "statepoint-num-patch-bytes": if the string value of this attribute
   can be parsed as an integer, then it is propagated to the `num patch
   bytes` parameter of the statepoint created.

This change intentionally does not assert on a malformed value for these
attributes, given that they're not "official" attributes.

Reviewers: reames, pgavlin

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D9735

llvm-svn: 237286

docs/Statepoints.rst

@@ -677,6 +677,21 @@ of this function is inserted at each poll site desired.  While calls or invokes
 inside this method are transformed to a ``gc.statepoints``, recursive poll 
 insertion is not performed.
 
+By default PlaceSafepoints passes in ``0xABCDEF00`` as the statepoint
+ID and ``0`` as the number of patchable bytes to the newly constructed
+``gc.statepoint``.  These values can be configured on a per-callsite
+basis using the attributes ``"statepoint-id"`` and
+``"statepoint-num-patch-bytes"``.  If a call site is marked with a
+``"statepoint-id"`` function attribute and its value is a positive
+integer (represented as a string), then that value is used as the ID
+of the newly constructed ``gc.statepoint``.  If a call site is marked
+with a ``"statepoint-num-patch-bytes"`` function attribute and its
+value is a positive integer, then that value is used as the 'num patch
+bytes' parameter of the newly constructed ``gc.statepoint``.  The
+``"statepoint-id"`` and ``"statepoint-num-patch-bytes"`` attributes
+are not propagated to the ``gc.statepoint`` call or invoke if they
+could be successfully parsed.
+
 If you are scheduling the RewriteStatepointsForGC pass late in the pass order,
 you should probably schedule this pass immediately before it.  The exception 
 would be if you need to preserve abstract frame information (e.g. for

lib/Transforms/Scalar/PlaceSafepoints.cpp

@@ -881,20 +881,52 @@ static Value *ReplaceWithStatepoint(const CallSite &CS, /* to replace */
 
   // Create the statepoint given all the arguments
   Instruction *Token = nullptr;
-  AttributeSet OriginalAttrs;
+
+  uint64_t ID;
+  uint32_t NumPatchBytes;
+
+  AttributeSet OriginalAttrs = CS.getAttributes();
+  Attribute AttrID =
+      OriginalAttrs.getAttribute(AttributeSet::FunctionIndex, "statepoint-id");
+  Attribute AttrNumPatchBytes = OriginalAttrs.getAttribute(
+      AttributeSet::FunctionIndex, "statepoint-num-patch-bytes");
+
+  AttrBuilder AttrsToRemove;
+  bool HasID = AttrID.isStringAttribute() &&
+               !AttrID.getValueAsString().getAsInteger(10, ID);
+
+  if (HasID)
+    AttrsToRemove.addAttribute("statepoint-id");
+  else
+    ID = 0xABCDEF00;
+
+  bool HasNumPatchBytes =
+      AttrNumPatchBytes.isStringAttribute() &&
+      !AttrNumPatchBytes.getValueAsString().getAsInteger(10, NumPatchBytes);
+
+  if (HasNumPatchBytes)
+    AttrsToRemove.addAttribute("statepoint-num-patch-bytes");
+  else
+    NumPatchBytes = 0;
+
+  OriginalAttrs = OriginalAttrs.removeAttributes(
+      CS.getInstruction()->getContext(), AttributeSet::FunctionIndex,
+      AttrsToRemove);
+
+  Value *StatepointTarget = NumPatchBytes == 0
+                                ? CS.getCalledValue()
+                                : ConstantPointerNull::get(cast<PointerType>(
+                                      CS.getCalledValue()->getType()));
 
   if (CS.isCall()) {
     CallInst *ToReplace = cast<CallInst>(CS.getInstruction());
     CallInst *Call = Builder.CreateGCStatepointCall(
-        0xABCDEF00, 0, CS.getCalledValue(), makeArrayRef(CS.arg_begin(), CS.arg_end()),
-        None, None, "safepoint_token");
+        ID, NumPatchBytes, StatepointTarget,
+        makeArrayRef(CS.arg_begin(), CS.arg_end()), None, None,
+        "safepoint_token");
     Call->setTailCall(ToReplace->isTailCall());
     Call->setCallingConv(ToReplace->getCallingConv());
 
-    // Before we have to worry about GC semantics, all attributes are legal
-    // TODO: handle param attributes
-    OriginalAttrs = ToReplace->getAttributes();
-
     // In case if we can handle this set of attributes - set up function
     // attributes directly on statepoint and return attributes later for
     // gc_result intrinsic.
@@ -915,14 +947,10 @@ static Value *ReplaceWithStatepoint(const CallSite &CS, /* to replace */
     // original block.
     Builder.SetInsertPoint(ToReplace->getParent());
     InvokeInst *Invoke = Builder.CreateGCStatepointInvoke(
-        0xABCDEF00, 0, CS.getCalledValue(), ToReplace->getNormalDest(),
+        ID, NumPatchBytes, StatepointTarget, ToReplace->getNormalDest(),
         ToReplace->getUnwindDest(), makeArrayRef(CS.arg_begin(), CS.arg_end()),
         Builder.getInt32(0), None, "safepoint_token");
 
-    // Currently we will fail on parameter attributes and on certain
-    // function attributes.
-    OriginalAttrs = ToReplace->getAttributes();
-
     // In case if we can handle this set of attributes - set up function
     // attributes directly on statepoint and return attributes later for
     // gc_result intrinsic.

test/Transforms/PlaceSafepoints/patchable-statepoints.ll

@@ -0,0 +1,44 @@
+; RUN: opt -place-safepoints -S < %s | FileCheck %s
+
+declare void @f()
+declare i32 @personality_function()
+
+define void @test_id() gc "statepoint-example" {
+; CHECK-LABEL: @test_id(
+entry:
+; CHECK-LABEL: entry:
+; CHECK: invoke i32 (i64, i32, void ()*, i32, i32, ...) @llvm.experimental.gc.statepoint.p0f_isVoidf(i64 100, i32 0, void ()* @f
+  invoke void @f()  "statepoint-id"="100" to label %normal_return unwind label %exceptional_return
+
+normal_return:
+  ret void
+
+exceptional_return:
+  %landing_pad4 = landingpad {i8*, i32} personality i32 ()* @personality_function cleanup
+  ret void
+}
+
+define void @test_num_patch_bytes() gc "statepoint-example" {
+; CHECK-LABEL: @test_num_patch_bytes(
+entry:
+; CHECK-LABEL: entry:
+; CHECK: invoke i32 (i64, i32, void ()*, i32, i32, ...) @llvm.experimental.gc.statepoint.p0f_isVoidf(i64 2882400000, i32 99, void ()* null,
+  invoke void @f()  "statepoint-num-patch-bytes"="99" to label %normal_return unwind label %exceptional_return
+
+normal_return:
+  ret void
+
+exceptional_return:
+  %landing_pad4 = landingpad {i8*, i32} personality i32 ()* @personality_function cleanup
+  ret void
+}
+
+declare void @do_safepoint()
+define void @gc.safepoint_poll() {
+entry:
+  call void @do_safepoint()
+  ret void
+}
+
+; CHECK-NOT: statepoint-id
+; CHECK-NOT: statepoint-num-patch_bytes