FP Assists

Metric Description

Certain floating point operations cannot be handled natively by the execution pipeline and must be performed by microcode (small programs injected into the execution stream). For example, when working with very small floating point values (so-called denormals), the floating-point units are not set up to perform these operations natively. Instead, a sequence of instructions to perform the computation on the denormal is injected into the pipeline. Since these microcode sequences might be hundreds of instructions long, these microcode assists are extremely deleterious to performance.

Possible Issues

A significant portion of execution time is spent in floating point assists.

Tips

Consider enabling the DAZ (Denormals Are Zero) and/or FTZ (Flush To Zero) options in your compiler to flush denormals to zero. This option may improve performance if the denormal values are not critical in your application. Also note that the DAZ and FTZ modes are not compatible with the IEEE Standard 754.

For more complete information about compiler optimizations, see our Optimization Notice.
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