RFR: 8351156: C1: Remove FPU stack support after 32-bit x86 removal [v2]

[Aleksey Shipilev]

On Thu, 27 Mar 2025 19:44:57 GMT, Vladimir Ivanov <vlivanov at openjdk.org> wrote:

>> Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains five commits:
>> 
>>  - Merge branch 'master' into JDK-8351156-x86-c1-fpustack
>>  - Fixing build failures after reg2stack
>>  - Remove remaining FPU uses in LIRAssembler_x86
>>  - Touchups
>>  - Initial fix
>
> src/hotspot/cpu/x86/c1_LIRAssembler_x86.cpp line 586:
> 
>> 584: 
>> 585:     case T_FLOAT: {
>> 586:       if (dest->is_single_xmm()) {
> 
> Time to turn it into an assert?

I think the intent for `ShouldNotReachHere()`-s in C1 code is to crash out on a gross error, instead of silently miscompiling. I would not be 100% sure src type and dst reg type are always correct. It is basically `guarantee` in disguise, AFAIU.

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PR Review Comment: https://git.openjdk.org/jdk/pull/24274#discussion_r2017533616