BMI2

Wetin you need know

How e dey work

PEXT dey gather selected input bit dem enter dense low-order result; PDEP dey scatter low-order input bit dem to position dem wey mask select. Other BMI2 instruction dem include BZHI, MULX, RORX, SHLX, SHRX and SARX. Dese dey operate on scalar integer register dem even though dem dey use VEX encoding.

Where e dey useful

Compact board representation or bitfield codec fit use PEXT/PDEP to map between dense and sparse bit layout dem. Dia execution cost dey vary well-well between implementation dem, so algorithm suppose benchmark representative input dem instead of assuming say short instruction sequence dey fast.

How to check support and enablement

CPUID.07H.00H:EBX bit 8 dey enumerate BMI2. Check di target-specific performance of di instruction dem wey dem actually use and keep dispatch outside code wey dem compile to require unsupported feature dem.

Check di exact instruction and operand shape instead make you just guess support from nearby extension. Scalar integer feature dem dey normally use general-purpose registers; encoding wey follow vector no mean say na vector-state requirement automatically.

Wetin di feature no dey guarantee

BMI2 no be AVX vector extension and e no require YMM state just because say di encoding na VEX. E no dey establish ADX or BMI1. MULX and normal multiplication dey different for register and flag behavior.

Compatibility and performance inside real life

Whether e work well depend on edge case dem as well as speed. Zero input, overflow, carry flag dem, operand size, alignment and memory ordering fit change how di code dey work. E better make you use compiler or library interface wey explain dis detail dem and give supported fallback.

Practical verification checklist

1. Record di exact processor or platform model plus di application, OS and runtime version dem wey dey involve. Make you keep di exact word dem wey di error or requirement use.
2. Check di manufacturer reference for dat exact model, den inspect di real capability and enabled state inside di environment where di program dey run.
3. Compare every single requirement of di binary or backend wey you choose. Name wey resemble am, alias, or broad technology label no reach.
4. Confirm say di application select di implementation wey dem intend. Use di diagnostics wey dem document and supported fallback if requirement dem no complete.
5. Make only one supported change at a time, den run di same workload again. Keep di original configuration and recovery way ready.

If dem list di feature but software no fit use am

Start from di exact component wey dey fail. Hardware database dey describe capability wey dem record; di operating system or hypervisor fit show different real environment. If illegal-instruction error happen, you still need to check di exact instruction wey cause di fault and di binary build, because corrupt file or anoda instruction wey no dey supported fit give di same kind problem.

Install di application, driver or runtime version wey get support for dat exact platform, and use di vendor documented baseline or fallback build if e need am. Software update no fit create instruction wey di processor no get. Firmware and security-policy change dem suppose follow di system manufacturer procedure and recovery plan, no be just any common optimization advice.

Related feature dem and useful difference dem

BMI1 · ADX · x86-64-v3

Sources and scope of dis explanation

Intel 64 and IA-32 Architectures Software Developer's Manual · x86-64 psABI: processor architecture and microarchitecture level dem

Dis reference dem establish architectural behavior and software requirement dem. Dem no dey independently verify every feature value for any linked hardware model page. For model support, use dat page manufacturer evidence and check di active system configuration. Dis article no supply benchmark, certification or independent review date.

Related

Dis entities connect to dis article. Type dey show for every link.

Sources and verification

Editorial ownership: Feex. No independent review date dey recorded. How we dey do research.

• Intel 64 and IA-32 Architectures Software Developer's Manual · Volume 1 and 2 describe di named instruction family dem and CPUID; Volume 3 describe state, paging, VMX and protection control dem. Architecture documentation no dey prove say particular model support am.
• x86-64 psABI: processor architecture and microarchitecture level dem · Machine Interface, Processor Architecture: baseline and cumulative v2/v3/v4 feature table, OS-state check dem and deployment recommendation dem.