8362515: RISC-V: cleanup NativeFarCall

[Hamlin-Li]

Hi,
Can you help to review this patch?

By https://github.com/openjdk/jdk/blob/master/src/hotspot/cpu/riscv/macroAssembler_riscv.hpp#L1270, there are far call, indirect call, reloc call.
NativeFarCall is in fact a reloc call, the name is confusing, better to rename it to RelocCall.
Also add some comments and do some other simple cleanup.

Thanks!

---

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Issue

• JDK-8362515: RISC-V: cleanup NativeFarCall (Enhancement - P4)

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[bridgekeeper]

👋 Welcome back mli! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

[openjdk]

❗ This change is not yet ready to be integrated.
See the Progress checklist in the description for automated requirements.

[openjdk]

@Hamlin-Li this pull request can not be integrated into master due to one or more merge conflicts. To resolve these merge conflicts and update this pull request you can run the following commands in the local repository for your personal fork:

git checkout cleanup-NativeFarCall
git fetch https://git.openjdk.org/jdk.git master
git merge FETCH_HEAD
# resolve conflicts and follow the instructions given by git merge
git commit -m "Merge master"
git push

[openjdk]

@Hamlin-Li The following label will be automatically applied to this pull request:

• hotspot-compiler

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing list. If you would like to change these labels, use the /label pull request command.

[mlbridge]

Webrevs

• 02: Full - Incremental (f72db245)
• 01: Full (1099e13a)
• 00: Full (da2500bc)

[RealFYang]

Is this change safe? Seems it modifies the original logic.

[Hamlin-Li]

Yes, MacroAssembler::pd_call_destination only call MacroAssembler::target_addr_for_insn.
And MacroAssembler::target_addr_for_insn are used in other places in NativeFarCall, so it's better to use target_addr_for_insn only to improve readability.

[RealFYang]

There seems to be a subtle differnece here. I see MacroAssembler::pd_call_destination delegates work to NativeFarCall::reloc_destination which calls MacroAssembler::target_addr_for_insn under condition if (stub_addr != nullptr). After this change, that condition is gone. I haven't looked into how this may make a difference.

I see this function was introduce by JDK-8332689, maybe @robehn could comment?

[1] https://github.com/openjdk/jdk/blob/master/src/hotspot/cpu/riscv/nativeInst_riscv.cpp#L112

[Hamlin-Li]

I see MacroAssembler::pd_call_destination delegates work to NativeFarCall::reloc_destination which calls MacroAssembler::target_addr_for_insn under condition if (stub_addr != nullptr).

Can you clarify "MacroAssembler::pd_call_destination delegates work to NativeFarCall::reloc_destination"?
Robbin is on vacation for weeks, so I'm afraid he's not going to reponse in time.

[Hamlin-Li]

I don't think this pr changes the logic in NativeFarCall::reloc_destination, am I right?
Or maybe you're misled by the name change from stub_address to reloc_destination_without_check and existing method reloc_destination()?

[RealFYang]

I see MacroAssembler::pd_call_destination delegates work to NativeFarCall::reloc_destination which calls MacroAssembler::target_addr_for_insn under condition if (stub_addr != nullptr).

Can you clarify "MacroAssembler::pd_call_destination delegates work to NativeFarCall::reloc_destination"? Robbin is on vacation for weeks, so I'm afraid he's not going to reponse in time.

Sorry for not being clear. Let me clarify. I mean this code snippet at [1]:

 74 address Relocation::pd_call_destination(address orig_addr) {
 75   assert(is_call(), "should be a call here");
 76   if (NativeCall::is_at(addr())) {
 77     return nativeCall_at(addr())->reloc_destination();           <======================
 78   }
 79
 80   if (orig_addr != nullptr) {

Before this change, we call MacroAssembler::pd_call_destination here.
And NativeFarCall::reloc_destination at L77 will only call MacroAssembler::target_addr_for_insn under condition if (stub_addr != nullptr) [2]. But we will always/unconditionally call MacroAssembler::target_addr_for_insn here after this change. That seems make a difference? Did I miss anything?

[1] https://github.com/openjdk/jdk/blob/master/src/hotspot/cpu/riscv/relocInfo_riscv.cpp#L77
[2] https://github.com/openjdk/jdk/blob/master/src/hotspot/cpu/riscv/nativeInst_riscv.cpp#L112

[Hamlin-Li]

The call path was:
Relocation::pd_call_destination(address orig_addr) =>
NativeCall::reloc_destination() =>
NativeFarCall::reloc_destination()

After change, it's:
Relocation::pd_call_destination(address orig_addr) =>
NativeCall::reloc_destination() =>
RelocCall::reloc_destination()

The code path does not change except that NativeFarCall::reloc_destination is changed to RelocCall::reloc_destination and assert(NativeFarCall... is changed to assert(RelocCall.
Seems it does not change any logic in this code path, but just names.

Before this change, we call MacroAssembler::pd_call_destination here.
And NativeFarCall::reloc_destination at L77 will only call MacroAssembler::target_addr_for_insn under condition if (stub_addr != nullptr)

The code between NativeFarCall::reloc_destination and RelocCall::reloc_destination is almost the same, except of names.

But we will always/unconditionally call MacroAssembler::target_addr_for_insn here after this change.

No. I guess you might have mistoken RelocCall::reloc_destination_without_check() as RelocCall::reloc_destination()?