Statepoint: Fix handling of Far Immediate calls

[swaroop.sridhar]

Summary

gc.statepoint intrinsics with a far immediate target was lowered incorrectly as a pc-rel32 call.

For example, for
%safepoint_token = call i32 (i64, i32, void ()*, i32, i32, ...) @llvm.experimental.gc.statepoint.p0f_isVoidf(i64 0, i32 0, void ()* inttoptr (i64 140727162896504 to void ()*), i32 0, i32 0, i32 0, i32 0)

the CALL instruction generated was:

callq 140727162896504

This change fixes the problem, so that an indirect call via a scratch register is correctly generated:

movabsq $140727162896504, %rax
callq *%rax

In lowerCallFromStatepoint(), the callee-target was modified and represented as a "TargetConstant" node, rather than a "Constant" node.
Undoing this modification enabled LowerCall() to generate the correct CALL instruction.

[sanjoy]

LGTM.

lib/CodeGen/SelectionDAG/StatepointLowering.cpp

 
   SDValue ActualCallee = Builder.getValue(ISP.getActualCallee());
 
-  // Handle immediate and symbolic callees.
-  if (auto *ConstCallee = dyn_cast<ConstantSDNode>(ActualCallee.getNode()))
-    ActualCallee = Builder.DAG.getIntPtrConstant(ConstCallee->getZExtValue(),
-                                                 Builder.getCurSDLoc(),
-                                                 /*isTarget=*/true);
-  else if (auto *SymbolicCallee =
-               dyn_cast<GlobalAddressSDNode>(ActualCallee.getNode()))
-    ActualCallee = Builder.DAG.getTargetGlobalAddress(
-        SymbolicCallee->getGlobal(), SDLoc(SymbolicCallee),
-        SymbolicCallee->getValueType(0));
-
   assert(CS.getCallingConv() != CallingConv::AnyReg &&
          "anyregcc is not supported on statepoints!");
 

test/CodeGen/X86/statepoint-far-call.ll

+; RUN: llc < %s | FileCheck %s
+; Test to check that Statepoints with X64 far-immediate targets
+; are lowered correctly to an indirect call via a scratch register.
+
+target datalayout = "e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-win64"
+
+define void @test_far_call() gc "statepoint-example" {
+; CHECK-LABEL: test_far_call
+; CHECK: pushq %rax
+; CHECK: movabsq $140727162896504, %rax 
+; CHECK: callq *%rax
+; CHECK: popq %rax
+; CHECK: retq
+
+entry:
+  %safepoint_token = call i32 (i64, i32, void ()*, i32, i32, ...) @llvm.experimental.gc.statepoint.p0f_isVoidf(i64 0, i32 0, void ()* inttoptr (i64 140727162896504 to void ()*), i32 0, i32 0, i32 0, i32 0)
+  ret void
+}
+
+declare i32 @llvm.experimental.gc.statepoint.p0f_isVoidf(i64, i32, void ()*, i32, i32, ...) 
+