Remove the additional constant which requires an extra register for statepoint lowering.

[linzj]

Summary

The newly-created constant zero will need an extra register to hold it
in the current statepoint lowering implementation. Remove it if there exists
one.

[arsenm]

llvm/lib/CodeGen/SelectionDAG/StatepointLowering.cpp

865–867

This loses using the right address space sized pointer

[linzj]

llvm/lib/CodeGen/SelectionDAG/StatepointLowering.cpp

865–867

Should I just assign ActualCallee with ConstCallee?

[linzj]

Use undef SDValue instead.

[arsenm]

LGTM

[linzj]

When the commit will be landed?

[arsenm]

In D67147#1894696, @linzj wrote:

When the commit will be landed?

If you need someone to commit a patch for you, you should explicitly state so. I can try to commit this in the next day or so

[linzj]

In D67147#1894703, @arsenm wrote:

In D67147#1894696, @linzj wrote:

When the commit will be landed?

If you need someone to commit a patch for you, you should explicitly state so. I can try to commit this in the next day or so

Yes. I need some one commit this for me. I am not a committer. Thank you for your help.

[arsenm]

Can you rebase this? I think a similar patch conflicts (a6f38b46972e4e6978c3a768001903d3f3334cb7)

[linzj]

D67147

In D67147#1894730, @arsenm wrote:

Can you rebase this? I think a similar patch conflicts (a6f38b46972e4e6978c3a768001903d3f3334cb7)

Okay

[linzj]

Rebase from the master.

[linzj]

Fix test case miss RUN comment.

[linzj]

Rebase again. I don't think the failed unit test is relevant to my change.

[linzj]

I think it's fine to go back to the main stream.

[linzj]

@arsenm , looks good to you?

[arsenm]

a58c8a78660896bfe7d5e0ca18b9ab7458dea92b

llvm/lib/CodeGen/SelectionDAG/StatepointLowering.cpp

if (ISP.getNumPatchBytes() > 0) {
     // `null` instead.  Not lowering the call target lets statepoint clients get
     // away without providing a physical address for the symbolic call target at
     // link time.
 
     const auto &TLI = DAG.getTargetLoweringInfo();
     const auto &DL = DAG.getDataLayout();
 
     unsigned AS = ISP.getCalledValue()->getType()->getPointerAddressSpace();
-    ActualCallee = DAG.getConstant(0, getCurSDLoc(), TLI.getPointerTy(DL, AS));
+    // Don't generate an extra constant if there is already one.
+    // Or it will ends up an extra MOV Constant to PhyReg instruction.
+    if (auto *ConstCallee =
+            dyn_cast<ConstantSDNode>(getValue(ISP.getCalledValue()))) {
+      ActualCallee =
+          DAG.getIntPtrConstant(ConstCallee->getZExtValue(), getCurSDLoc(),
+                                /*isTarget=*/true);
+    } else {
+      ActualCallee =
+          DAG.getConstant(0, getCurSDLoc(), TLI.getPointerTy(DL, AS));
+    }
   } else {
     ActualCallee = getValue(ISP.getCalledValue());
   }
 
   StatepointLoweringInfo SI(DAG);
   populateCallLoweringInfo(SI.CLI, ISP.getCall(),
                            ImmutableStatepoint::CallArgsBeginPos,
                            ISP.getNumCallArgs(), ActualCallee,

llvm/test/CodeGen/X86/statepoint-no-extra-const.ll

+define i8 addrspace(1)* @no_extra_const(i8 addrspace(1)* %obj) gc "statepoint-example" {
+; CHECK-LABEL:   no_extra_const:
+; CHECK:         .cfi_startproc
+; CHECK-NEXT:    # %bb.0:                                # %entry
+; CHECK-NEXT:    pushq  %rax
+; CHECK-NEXT:    .cfi_def_cfa_offset 16
+; CHECK-NEXT:    movq %rdi, (%rsp)
+; CHECK-NEXT:    nopl 8(%rax)
+; CHECK-NEXT:    .Ltmp0:
+; CHECK-NEXT:    movq (%rsp), %rax
+; CHECK-NEXT:    popq %rcx
+; CHECK-NEXT:    .cfi_def_cfa_offset 8
+; CHECK-NEXT:    retq
+entry:
+  %safepoint_token = call token (i64, i32, void ()*, i32, i32, ...) @llvm.experimental.gc.statepoint.p0f_isVoidf(i64 0, i32 4, void ()* null, i32 0, i32 0, i32 0, i32 0, i8 addrspace(1)* %obj)
+  %obj.relocated = call coldcc i8 addrspace(1)* @llvm.experimental.gc.relocate.p1i8(token %safepoint_token, i32 7, i32 7) ; (%obj, %obj)
+  ret i8 addrspace(1)* %obj.relocated
+}
+
+declare token @llvm.experimental.gc.statepoint.p0f_isVoidf(i64, i32, void ()*, i32, i32, ...)
+declare i8 addrspace(1)* @llvm.experimental.gc.relocate.p1i8(token, i32, i32)