commit 0c6a151c65285987f5daabc7f76fe57a82b45ab1
author Benoit Jacob <jacob.benoit.1@gmail.com> Thu Oct 17 18:14:19 2024 -0400
committer GitHub <noreply@github.com> Thu Oct 17 18:14:19 2024 -0400
tree dd71395021f3dae592a49893905adeeed9e832b0
parent fecccdc852a7e2dda30cbb924427634acb7eb820

Warn when --iree-llvmcpu-target-cpu defaults to "generic". (#18682)

Progress on https://github.com/iree-org/iree/issues/18561. This
introduces a warning (which we intend to promote to an error in the
future) when targeting a generic CPU without explicitly asking for it.
This addresses a performance footgun as that IREE default results in low
performance.

Along the way this grew into a substantial change to e2e testing rules:
- `TARGET_CPU` and `TARGET_CPU_FEATURES` arguments are gone (were
redundant with `COMPILER_FLAGS`).
- For `TARGET_CPU_FEATURES_VARIANTS`, the special value `"default"` is
renamed to `"generic"` and a new value `"host"` is also supported.

Example warning (this is customized to the target architecture, here
x86):

```
/home/benoit/matmul_i8.mlir:0:0: warning: while creating CPU target: 
Defaulting to targeting a generic CPU for the target architecture will result in poor performance. Please specify a target CPU and/or a target CPU feature set. If it is intended to target a generic CPU, specify "generic" as the CPU.

This can be done in two ways:
1. With command-line flags:
    --iree-llvmcpu-target-cpu=...
    --iree-llvmcpu-target-cpu-features=...
2. Within the IR:
    #hal.executable.target< ... , cpu="...", cpu_features="...">

In the rest of this message, these fields are referred to as just `cpu` and `cpu_features`.

Examples:

    cpu=generic
        Target a generic CPU of the target architecture. The generated code will have poor performance, but will run on any CPU.

    cpu=host
        Target the host CPU. The generated code will have optimal performance on the host CPU but will crash on other CPUs not supporting the same CPU features.

    cpu="name"
        Target a specific CPU. This is mostly used on x86. The accepted values are the same as in Clang command lines.
        List of accepted x86 CPUs: nocona, core2, penryn, bonnell, atom, silvermont, slm, goldmont, goldmont-plus, tremont, nehalem, corei7, westmere, sandybridge, corei7-avx, ivybridge, core-avx-i, haswell, core-avx2, broadwell, skylake, skylake-avx512, skx, cascadelake, cooperlake, cannonlake, icelake-client, rocketlake, icelake-server, tigerlake, sapphirerapids, alderlake, raptorlake, meteorlake, arrowlake, arrowlake-s, lunarlake, gracemont, pantherlake, sierraforest, grandridge, graniterapids, graniterapids-d, emeraldrapids, clearwaterforest, knl, knm, k8, athlon64, athlon-fx, opteron, k8-sse3, athlon64-sse3, opteron-sse3, amdfam10, barcelona, btver1, btver2, bdver1, bdver2, bdver3, bdver4, znver1, znver2, znver3, znver4, znver5, x86-64, x86-64-v2, x86-64-v3, x86-64-v4

    cpu_features="+feature1,..."
        Target a CPU supporting the comma-separated of (+-prefixed) features. The accepted values are the same as in Clang command lines.
```

---------

Signed-off-by: Benoit Jacob <jacob.benoit.1@gmail.com>