simdgen

Overview ¶

simdgen is an experiment in generating Go <-> asm SIMD mappings.

Usage: simdgen [-xedPath=path] [-q=query] input.yaml...

If -xedPath is provided, one of the inputs is a sum of op-code definitions generated from the Intel XED data at path.

If input YAML files are provided, each file is read as an input value. See unify.Closure.UnmarshalYAML or "go doc unify.Closure.UnmarshalYAML" for the format of these files.

TODO: Example definitions and values.

The command unifies across all of the inputs and prints all possible results of this unification.

If the -q flag is provided, its string value is parsed as a value and treated as another input to unification. This is intended as a way to "query" the result, typically by narrowing it down to a small subset of results.

Typical usage:

go run . -xedPath $XEDPATH *.yaml

To see just the definitions generated from XED, run:

go run . -xedPath $XEDPATH

(This works because if there's only one input, there's nothing to unify it with, so the result is simply itself.)

To see just the definitions for VPADDQ:

go run . -xedPath $XEDPATH -q '{asm: VPADDQ}'

simdgen can also generate Go definitions of SIMD mappings: To generate go files to the go root, run:

go run . -xedPath $XEDPATH -o godefs -goroot $PATH/TO/go go.yaml categories.yaml types.yaml

types.yaml is already written, it specifies the shapes of vectors. categories.yaml and go.yaml contains definitions that unifies with types.yaml and XED data, you can find an example in ops/AddSub/.

When generating Go definitions, simdgen do 3 "magic"s: - It splits masked operations(with op's [Masked] field set) to const and non const:

• One is a normal masked operation, the original
• The other has its mask operand's [Const] fields set to "K0".
• This way the user does not need to provide a separate "K0"-masked operation def.

- It deduplicates intrinsic names that have duplicates:

• If there are two operations that shares the same signature, one is AVX512 the other is before AVX512, the other will be selected.
• This happens often when some operations are defined both before AVX512 and after. This way the user does not need to provide a separate "K0" operation for the AVX512 counterpart.

- It copies the op's ConstImm field to its immediate operand's [Const] field.

• This way the user does not need to provide verbose op definition while only the const immediate field is different. This is useful to reduce verbosity of compares with imm control predicates.

These 3 magics could be disabled by enabling -nosplitmask, -nodedup or -noconstimmporting flags.

simdgen right now only supports amd64, -arch=$OTHERARCH will trigger a fatal error.