[riscv-port-jdk11u:riscv-port] RFR: 8294366: RISC-V: Partially mark out incompressible regions

[Fei Yang]

On Wed, 16 Oct 2024 14:08:57 GMT, Dingli Zhang <dzhang at openjdk.org> wrote:

> Hi,
> Please help review this backport to riscv-port-jdk11u.
> 
> Backport of [JDK-8294366](https://bugs.openjdk.org/browse/JDK-8294366).
> 
> The original patch cannot be directly applied because of riscv-port-jdk11u do not have `BarrierSetAssembler::nmethod_entry_barrier`, [JDK-8223173](https://bugs.openjdk.org/browse/JDK-8223173) or [JDK-8223173](https://bugs.openjdk.org/browse/JDK-8293007).
> 
> Testing:
> - Tier1 passed without new failure on lp4a (release).

Changes requested by fyang (Lead).

src/hotspot/cpu/riscv/c1_MacroAssembler_riscv.cpp line 324:

> 322:   // must ensure that this first instruction is a J, JAL or NOP.
> 323:   // Make it a NOP.
> 324:   IncompressibleRegion ir(this);  // keep the nop as 4 bytes for patching.

I think you should move the `assert_alignment(pc())` in `C1_MacroAssembler::verified_entry` here before this nop. Seens that assertion was miss-placed by previous backport PR: https://github.com/openjdk/riscv-port-jdk11u/pull/40

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PR Review: https://git.openjdk.org/riscv-port-jdk11u/pull/43#pullrequestreview-2373997065
PR Review Comment: https://git.openjdk.org/riscv-port-jdk11u/pull/43#discussion_r1804011301