RFR: 8288971: AArch64: Clean up stack and register handling in interpreter

[Nick Gasson]

On Wed, 22 Jun 2022 13:00:44 GMT, Andrew Haley <aph at openjdk.org> wrote:

> There are several places in the interpreter that could be improved.
> 
> 1. We use r13 to pass the caller's SP to a callee through adapters. r13 is not a callee-saved register in the native ABI, so this causes some complications. Use a callee-saved register.
> 2. We frequently recalculate the location where the native SP needs to go. We have a spare slot in the interpreter frame, so we should calculate it once, when the frame is created, and use it.
> 3. Related to 1, we should clearly label all the places where the caller's SP is passed to a callee.

src/hotspot/cpu/aarch64/assembler_aarch64.hpp line 156:

> 154: REGISTER_DECLARATION(Register, esp,      r20);
> 155: // Sender's SP while in interpreter
> 156: REGISTER_DECLARATION(Register, r19_sender_sp, r19);

I don't think rmonitors above is used anywhere, perhaps you could reuse r25? Or at least delete the definition of rmonitors while you're editing this.

src/hotspot/cpu/aarch64/interp_masm_aarch64.hpp line 98:

> 96:   void check_extended_sp(const char* msg = "check extended SP") {
> 97: #ifdef ASSERT
> 98:       Label L;

Should be two space indent here

src/hotspot/cpu/aarch64/templateInterpreterGenerator_aarch64.cpp line 1430:

> 1428: 
> 1429:   // Restore SP (drop native parameters area), to keep SP in sync with extended_sp in frame
> 1430:   // __ restore_sp_after_call();

This seems to happen further down, around line 1530, but it's interleaved with popping the frame. Is there a reason to have the commented out call here?

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PR: https://git.openjdk.org/jdk/pull/9239