LDMXCSR

Load MXCSR Register

stableVMJITAOTinstruction

Encodings

Operand encoding

Each mode is a value of the Op/En column above. It says which field of the encoded instruction carries each operand, in the order they are written, and whether the instruction reads it, writes it or both.

Measured cost

Description#

Loads the source operand into the MXCSR control/status register. The source operand is a 32-bit memory location. See "MXCSR Control and Status Register" in Chapter 10, of the Intel(R) 64 and IA-32 Architectures Software Developer's Manual, Volume 1, for a description of the MXCSR register and its contents.

The LDMXCSR instruction is typically used in conjunction with the (V)STMXCSR instruction, which stores the contents of the MXCSR register in memory.

The default MXCSR value at reset is 1F80H.

If a (V)LDMXCSR instruction clears a SIMD floating-point exception mask bit and sets the corresponding exception flag bit, a SIMD floating-point exception will not be immediately generated. The exception will be generated only upon the execution of the next instruction that meets both conditions below:

• the instruction must operate on an XMM or YMM register operand, * the instruction causes that particular SIMD floating-point exception to be reported.

This instruction's operation is the same in non-64-bit modes and 64-bit mode.

If VLDMXCSR is encoded with VEX.L= 1, an attempt to execute the instruction encoded with VEX.L= 1 will cause an #UD exception.

Note: In VEX-encoded versions, VEX.vvvv is reserved and must be 1111b, otherwise instructions will #UD.

Operation#

MXCSR := m32;

C/C++ Compiler Intrinsic Equivalent
_mm_setcsr(unsigned int i)

Numeric Exceptions#

None.

Other Exceptions#

See Table 2-22, "Type 5 Class Exception Conditions," additionally:

#GP                 For an attempt to set reserved bits in MXCSR.

#UD                 If VEX.vvvv  1111B.

Sources

• This instruction in the Intel manual
• Latency and throughput per microarchitecture