RFR: 8266609: AArch64: include FP/LR space in LIR_Assembler::initial_frame_size_in_bytes()

[Nick Gasson]

On Thu, 6 May 2021 10:30:11 GMT, Andrew Haley <aph at openjdk.org> wrote:

> This calculation is the same as x86. Can you explain why it has to be changed on AArch64, but should not be changed on x86?

On AArch64 `C1_MacroAssembler::build_frame()` delegates to `MacroAssembler::build_frame()` which expects the total frame size. On x86 we build the frame directly in C1_MacroAssembler by doing roughly `__ push(rbp); __ decrement(rsp, frame_size_in_bytes);` so it's natural that `frame_size_in_bytes` shouldn't include the space for the frame pointer and the return address (which was already pushed by the `call` instruction). If we made this change on x86 we'd need to subtract `2*wordSize` from each increment/decrement of rsp which seems like a net loss.

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PR: https://git.openjdk.java.net/jdk/pull/3898