[Statepoint] Remove redundant clear of call target on register

Patchable statepoint is lowered into sequence of nops, so zeroed call target
should not be on register. It is better to use getTargetConstant instead
of getConstant to select zero constant for call target.

Reviewers: reames
Reviewed By: reames
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D74465

Author: Serguei Katkov

llvm/lib/CodeGen/SelectionDAG/StatepointLowering.cpp

@@ -859,7 +859,8 @@ SelectionDAGBuilder::LowerStatepoint(ImmutableStatepoint ISP,
     const auto &DL = DAG.getDataLayout();
 
     unsigned AS = ISP.getCalledValue()->getType()->getPointerAddressSpace();
-    ActualCallee = DAG.getConstant(0, getCurSDLoc(), TLI.getPointerTy(DL, AS));
+    ActualCallee =
+        DAG.getTargetConstant(0, getCurSDLoc(), TLI.getPointerTy(DL, AS));
   } else {
     ActualCallee = getValue(ISP.getCalledValue());
   }

llvm/test/CodeGen/X86/statepoint-call-lowering.ll

@@ -141,7 +141,6 @@ define i1 @test_i1_return_patchable() gc "statepoint-example" {
 ; CHECK:       # %bb.0: # %entry
 ; CHECK-NEXT:    pushq %rax
 ; CHECK-NEXT:    .cfi_def_cfa_offset 16
-; CHECK-NEXT:    xorl %eax, %eax
 ; CHECK-NEXT:    nopl (%rax)
 ; CHECK-NEXT:  .Ltmp7:
 ; CHECK-NEXT:    popq %rcx