[riscv-port] RFR: 8278322: riscv: Support RVC: compressed instructions

[Yadong Wang]

On Tue, 7 Dec 2021 04:46:10 GMT, Xiaolin Zheng <xlinzheng at openjdk.org> wrote:

> About the _nc postfix of some of Assembler instructions: we know a bunch of places should be reserved for patching, where we cannot change them into compressed instructions. _nc is short for not compressible - with this, those instructions should keep their origin 4-byte form and remain uncompressed.

Why the compressed instructions can not be patched?

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PR: https://git.openjdk.java.net/riscv-port/pull/24