PR #16585: Add support for float8_e4m3 and float8_e3m4 types

[copybara-service]

PR #16585: Add support for float8_e4m3 and float8_e3m4 types

Imported from GitHub PR #16585

This PR adds f8E4M3 and f8E3M4 types support to XLA (mainly to cpu_compiler).

f8E4M3 type follows IEEE 754 convention.

f8E4M3 (IEEE 754)
- Exponent bias: 7
- Maximum stored exponent value: 14 (binary 1110)
- Maximum unbiased exponent value: 14 - 7 = 7
- Minimum stored exponent value: 1 (binary 0001)
- Minimum unbiased exponent value: 1 − 7 = −6
- Precision specifies the total number of bits used for the significand (mantisa), 
    including implicit leading integer bit = 3 + 1 = 4
- Follows IEEE 754 conventions for representation of special values
- Has Positive and Negative zero
- Has Positive and Negative infinity
- Has NaNs

Additional details:
- Max exp (unbiased): 7
- Min exp (unbiased): -6
- Infinities (+/-): S.1111.000
- Zeros (+/-): S.0000.000
- NaNs: S.1111.{001, 010, 011, 100, 101, 110, 111}
- Max normal number: S.1110.111 = +/-2^(7) x (1 + 0.875) = +/-240
- Min normal number: S.0001.000 = +/-2^(-6)
- Max subnormal number: S.0000.111 = +/-2^(-6) x 0.875 = +/-2^(-9) x 7
- Min subnormal number: S.0000.001 = +/-2^(-6) x 0.125 = +/-2^(-9)

f8E3M4 type follows IEEE 754 convention

f8E3M4 (IEEE 754)
- Exponent bias: 3
- Maximum stored exponent value: 6 (binary 110)
- Maximum unbiased exponent value: 6 - 3 = 3
- Minimum stored exponent value: 1 (binary 001)
- Minimum unbiased exponent value: 1 − 3 = −2
- Precision specifies the total number of bits used for the significand (mantissa), 
    including implicit leading integer bit = 4 + 1 = 5
- Follows IEEE 754 conventions for representation of special values
- Has Positive and Negative zero
- Has Positive and Negative infinity
- Has NaNs

Additional details:
- Max exp (unbiased): 3
- Min exp (unbiased): -2
- Infinities (+/-): S.111.0000
- Zeros (+/-): S.000.0000
- NaNs: S.111.{0,1}⁴ except S.111.0000
- Max normal number: S.110.1111 = +/-2^(6-3) x (1 + 15/16) = +/-2^3 x 31 x 2^(-4) = +/-15.5
- Min normal number: S.001.0000 = +/-2^(1-3) x (1 + 0) = +/-2^(-2)
- Max subnormal number: S.000.1111 = +/-2^(-2) x 15/16 = +/-2^(-2) x 15 x 2^(-4) = +/-15 x 2^(-6)
- Min subnormal number: S.000.0001 = +/-2^(-2) x 1/16 =  +/-2^(-2) x 2^(-4) = +/-2^(-6)

Testing:

bazel test \
//xla:array2d_test \
//xla:fp_util_test \
//xla:literal_comparison_test \
//xla:literal_test \
//xla/mlir/utils:type_util_test \
//xla:primitive_util_test \
//xla/python/ifrt:dtype_test \
//xla/python:xla_client_test \
//xla/service:elemental_ir_emitter_test \
//xla/service:float_normalization_test \
//xla/service/gpu/tests:float_conversions_test \
//xla/tests:array_elementwise_ops_test \
//xla/tests:constants_test \
//xla/tests:convert_test \
//xla/tests:float8_test \
//xla:util_test

bazel test \
//xla/hlo/translate/hlo_to_mhlo/tests:import.hlo.test \
//xla/hlo/translate/mhlo_to_hlo/tests:export.mlir.test \
//xla/mlir_hlo/tests:Dialect/mhlo/hlo-legalize-to-stablehlo.mlir.test \
//xla/mlir_hlo/tests:Dialect/mhlo/ops.mlir.test \
//xla/mlir_hlo/tests:Dialect/mhlo/stablehlo-legalize-to-hlo.mlir.test

Related PRs:

• LLVM PR-97179 [APFloat] Add support for f8E4M3 IEEE 754 type (Merged)
• LLVM PR-97118 [MLIR] Add f8E4M3 IEEE 754 type (Merged)
• LLVM PR-99698 [APFloat] Add support for f8E3M4 IEEE 754 type (Merged)
• LLVM PR-101230 [MLIR] Add f8E3M4 IEEE 754 type (Merged)
• StableHLO PR-2486 [RFC] Add f8E4M3 and f8E3M4 types support (Merged)
• StableHLO PR-2482 Add f8E4M3 and f8E3M4 types support (Merged)
• ml_dtypes PR-161 Add float8_e4m3 (Merged)
• ml_dtypes PR-171 Add float8_e3m4 (Merged)
• XLA PR-17075 [TSL] Bump ml_dtypes. Add float8_e4m3, float8_e3m4 (Approved)
• XLA PR-3200 Add support for float8_e4m3fnuz and float8_e5m2fnuz (Template)
• JAX PR-23585 Add float8_e4m3 type support (in Review)
  Copybara import of the project:

--
ec1c723 by Alexander Pivovarov [email protected]:

Add support for float8_e4m3 and float8_e3m4 types

Merging this change closes #16585

FUTURE_COPYBARA_INTEGRATE_REVIEW=#16585 from apivovarov:float8_e4m3 ec1c723