VZEROUPPER—Zero Upper Bits of YMM Registers

Opcode/Instruction	Op/En	64/32 bit Mode Support	CPUID Feature Flag	Description
VEX.128.0F.WIG 77 VZEROUPPER	NP	V/V	AVX	Zero upper 128 bits of all YMM registers.

Opcode/Instruction

Op/En

64/32 bit Mode Support

CPUID Feature Flag

Description

VEX.128.0F.WIG 77

VZEROUPPER

V/V

AVX

Zero upper 128 bits of all YMM registers.

Instruction Operand Encoding

Op/En	Operand 1	Operand 2	Operand 3	Operand 4
NP	NA	NA	NA	NA

Description

The instruction zeros the bits in position 128 and higher of all YMM registers. The lower 128-bits of the registers (the corresponding XMM registers) are unmodified.

This instruction is recommended when transitioning between AVX and legacy SSE code - it will eliminate perfor-mance penalties caused by false dependencies.

Note: VEX.vvvv is reserved and must be 1111b otherwise instructions will #UD. In Compatibility and legacy 32-bit mode only the lower 8 registers are modified.

Operation

VZEROUPPER

IF (64-bit mode)
    YMM0[VLMAX-1:128] ← 0
    YMM1[VLMAX-1:128] ← 0
    YMM2[VLMAX-1:128] ← 0
    YMM3[VLMAX-1:128] ← 0
    YMM4[VLMAX-1:128] ← 0
    YMM5[VLMAX-1:128] ← 0
    YMM6[VLMAX-1:128] ← 0
    YMM7[VLMAX-1:128] ← 0
    YMM8[VLMAX-1:128] ← 0
    YMM9[VLMAX-1:128] ← 0
    YMM10[VLMAX-1:128] ← 0
    YMM11[VLMAX-1:128] ← 0
    YMM12[VLMAX-1:128] ← 0
    YMM13[VLMAX-1:128] ← 0
    YMM14[VLMAX-1:128] ← 0
    YMM15[VLMAX-1:128] ← 0
ELSE
    YMM0[VLMAX-1:128] ← 0
    YMM1[VLMAX-1:128] ← 0
    YMM2[VLMAX-1:128] ← 0
    YMM3[VLMAX-1:128] ← 0
    YMM4[VLMAX-1:128] ← 0
    YMM5[VLMAX-1:128] ← 0
    YMM6[VLMAX-1:128] ← 0
    YMM7[VLMAX-1:128] ← 0
    YMM8-15: unmodified
FI

Intel C/C++ Compiler Intrinsic Equivalent

VZEROUPPER:

_mm256_zeroupper()

SIMD Floating-Point Exceptions

None.

Other Exceptions

See Exceptions Type 8.