RFR: 8339698: x86 andw/orw/xorw encoding missing 0x66 prefix

[Jatin Bhateja]

On Sat, 7 Sep 2024 02:00:49 GMT, Sandhya Viswanathan <sviswanathan at openjdk.org> wrote:

> x86 andw/orw/xorw encoding is missing 0x66 prefix. This bug was discovered as part of the x86 instruction encoding test generation tool and gtest ([JDK-8339507](https://bugs.openjdk.org/browse/JDK-8339507)). This fix is a precursor to the PR for JDK-8339507 (https://github.com/openjdk/jdk/pull/20857).
> 
> Best Regards,
> Sandhya

Marked as reviewed by jbhateja (Reviewer).

src/hotspot/cpu/x86/assembler_x86.cpp line 1636:

> 1634: 
> 1635: void Assembler::andw(Register dst, Register src) {
> 1636:   emit_int8(0x66);

This is operand-size override prefix which modifies the default operand size to 16bits.

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PR Review: https://git.openjdk.org/jdk/pull/20901#pullrequestreview-2288611187
PR Review Comment: https://git.openjdk.org/jdk/pull/20901#discussion_r1749373098