RFR: 8280476: [macOS] : hotspot arm64 bug exposed by latest clang

[Daniel D.Daugherty]

On Sat, 29 Jan 2022 08:16:26 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

>> A trivial fix to solve undefined behavior in src/hotspot/cpu/aarch64/immediate_aarch64.cpp:
>> replicate().
>> 
>> I was not able to reproduce the reported failure using:
>> 
>>   Xcode: Version 13.2.1 (13C100) which includes clang Apple LLVM 13.0.0 (clang-1300.0.29.30)
>> 
>> so I'm moving forward with the proposed fix from a code inspection
>> point of view.
>> 
>> I've tested this fix with Mach5 Tier[1-6]. Tier1 and Tier2 have completed with
>> no failures. Tier[3-6] are still running.
>
> src/hotspot/cpu/aarch64/immediate_aarch64.cpp line 136:
> 
>> 134:   if (nbits == 64) {
>> 135:     assert(count <= 1, "must be");
>> 136:     return bits;
> 
> For consistency with the < 64 case, shouldn't this be `return (count == 0) ? 0 : bits;` ?

@kimbarrett - Thanks for the review! Good catch! I believe you are correct,
but let's wait for @adinn to chime in here.

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PR: https://git.openjdk.java.net/jdk/pull/7270