Microsoft Specific

Tells the compiler not to insert Spectre variant 1 speculative execution barrier instructions for a function.


__declspec( spectre(nomitigation) )


The /Qspectre compiler option causes the compiler to insert speculative execution barrier instructions. They're inserted where analysis indicates that a Spectre variant 1 security vulnerability exists. The specific instructions emitted depend on the processor. While these instructions should have a minimal impact on code size or performance, there may be cases where your code is not affected by the vulnerability, and requires maximum performance.

Expert analysis might determine that a function is safe from a Spectre variant 1 bounds check bypass defect. In that case, you can suppress the generation of mitigation code within a function by applying __declspec(spectre(nomitigation)) to the function declaration.


The /Qspectre speculative execution barrier instructions provide important security protection and have a negligible affect on performance. Therefore, we recommend that you do not suppress them, except in the rare case where the performance of a function is a critical concern and the function is known to be safe.


The following code shows how to use __declspec(spectre(nomitigation)).

// compile with: /c /Qspectre
static __declspec(spectre(nomitigation))
int noSpectreIssues() {
    // No Spectre variant 1 vulnerability here
    // ...
    return 0;

int main() {
    return 0;

END Microsoft Specific

See also