WAIT, FWAIT

Wait

stableVMJITAOTinstruction

Encodings

Measured cost

Description#

Causes the processor to check for and handle pending, unmasked, floating-point exceptions before proceeding. (FWAIT is an alternate mnemonic for WAIT.)

This instruction is useful for synchronizing exceptions in critical sections of code. Coding a WAIT instruction after a floating-point instruction ensures that any unmasked floating-point exceptions the instruction may raise are handled before the processor can modify the instruction's results. See the section titled "Floating-Point Exception Synchronization" in Chapter 8 of the Intel(R) 64 and IA-32 Architectures Software Developer's Manual, Volume 1, for more information on using the WAIT/FWAIT instruction.

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

Operation#

CheckForPendingUnmaskedFloatingPointExceptions;

FPU Flags Affected
The C0, C1, C2, and C3 flags are undefined.

Floating-Point Exceptions#

None.

Exceptions

Sources

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