[#llvm-MCInstrAnalysis-isZeroIdiom]
= xref:llvm.adoc[llvm]::xref:llvm/MCInstrAnalysis.adoc[MCInstrAnalysis]::isZeroIdiom
:relfileprefix: ../../
:mrdocs:

Returns true if MI is a dependency breaking zero‐idiom for the given subtarget.

== Synopsis

Declared in `<llvm/MC/MCInstrAnalysis.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
virtual
bool
isZeroIdiom(
    xref:llvm/MCInst.adoc[MCInst] const& MI,
    xref:llvm/APInt.adoc[APInt]& Mask,
    unsigned int CPUID) const;
----

== Description

Mask is used to identify input operands that have their dependency broken. Each bit of the mask is associated with a specific input operand. Bits associated with explicit input operands are laid out first in the mask; implicit operands come after explicit operands.

Dependencies are broken only for operands that have their corresponding bit set. Operands that have their bit cleared, or that don't have a corresponding bit in the mask don't have their dependency broken. Note that Mask may not be big enough to describe all operands. The assumption for operands that don't have a correspondent bit in the mask is that those are still data dependent.

The only exception to the rule is for when Mask has all zeroes. A zero mask means: dependencies are broken for all explicit register operands.

== Return Value

True if `MI` is a dependency‐breaking zero‐idiom for `CPUID.`

== Parameters

[cols="1,4"]
|===
| Name| Description
| *MI*
| ‐ Instruction to test as a zero‐idiom.
| *Mask*
| ‐ [out]Operand mask identifying broken dependencies.
| *CPUID*
| ‐ Subtarget identifier selecting dependency rules.
|===


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