RFR: 8332689: RISC-V: Use load instead of trampolines [v22]

[Robbin Ehn]

On Thu, 4 Jul 2024 11:04:52 GMT, Fei Yang <fyang at openjdk.org> wrote:

>> I used to be excplicit about this is the normal **ld**.
>> But I see I did not do the same for **jalr** => **_jalr**. (as we are in MASM we can use 'private' method).
>> I'll change to normal ld and add an assert that we are in a incompressable region?
>> 
>> (I would like to revert that at some time, so the user of reloc_call don't need to know about it needs incompressable for reloc_call)
>> 
>> Suggested:
>> 
>> @@ -982,0 +983 @@ void MacroAssembler::load_link_jump(const address source, Register temp) {
>> +  assert(!in_compressible_region(), "Must be");
>> @@ -987 +988 @@ void MacroAssembler::load_link_jump(const address source, Register temp) {
>> -  Assembler::_ld(temp, temp, ((int32_t)distance << 20) >> 20);
>> +  Assembler::ld(temp, temp, ((int32_t)distance << 20) >> 20);
>
> Seems no need to worry about that? I think it's up to the caller to decide if it wants compressed instructions.
> Here in this case, the only call site is within a relocate() which will disable compressed instructions for you[1].
> 
>   relocate(entry.rspec(), [&] {
>     load_link_jump(target);
>   });
> 
> [1] https://github.com/openjdk/jdk/blob/master/src/hotspot/cpu/riscv/assembler_riscv.hpp#L2130

When you use reloc_call the size of the call must be an exact size we already specified (3 * NativeInstruction::instruction_size). (if those sizes don't apply you don't want a reloc_call) 
So there is nothing to choose from the caller prespective.

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PR Review Comment: https://git.openjdk.org/jdk/pull/19453#discussion_r1665703906