AVX-512指令编码-{er}含义 [英] AVX-512 Instruction Encoding - {er} Meaning

问题描述

在《英特尔x86指令集参考》中，有许多AVX-512指令在指令中带有可选的{er}.例如，一种形式的VADDPD被定义为

In the Intel x86 Instruction Set Reference, there are a number of AVX-512 instructions that have an optional {er} in the instruction. For example, one form of VADDPD is defined as

EVEX.NDS.512.66.0F.W1 58 /r
VADDPD zmm1 {k1}{z}, zmm2,
zmm3/m512/m64bcst{er}

{er}是什么意思?

What does the {er} mean?

推荐答案

摘自Intel SDM Volume 2A，3.1.1.3操作码摘要表中的指令列":

From Intel SDM Volume 2A, 3.1.1.3 " Instruction Column in the Opcode Summary Table":

{er}-表示支持嵌入式舍入控制，仅适用于寄存器-寄存器形式该指令.这也意味着支持SAE(禁止所有异常).

{er} — Indicates support for embedded rounding control, which is only applicable to the register-register form of the instruction. This also implies support for SAE (Suppress All Exceptions).

之前的2.6.8节指出，{er}在适用时可以在EVEX.L´L中进行编码:

Section 2.6.8 a bit earlier states that {er}, when applicable, can be encoded in EVEX.L´L:

EVEX编码系统中嵌入的静态舍入控制仅适用于在两个不同的向量长度处具有舍入语义的浮点指令:(i)标量，(ii)512位.同时在这种情况下，如果设置了EVEX.b，则字段EVEX.L’L表示舍入模式控制优先于MXCSR.RC.当EVEX.b是设置为禁止所有例外".处理器的行为就像设置了所有MXCSR掩码控件一样.

Static rounding control embedded in the EVEX encoding system applies only to register-to-register flavor of floating-point instructions with rounding semantic at two distinct vector lengths: (i) scalar, (ii) 512-bit. In both cases, the field EVEX.L’L expresses rounding mode control overriding MXCSR.RC if EVEX.b is set. When EVEX.b is set, "suppress all exceptions" is implied. The processor behaves as if all MXCSR masking controls are set.

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