Add rounding mode attribute to `arith`. This attribute can be used in
different FP `arith` operations to control rounding mode. Rounding modes
correspond to IEEE 754-specified rounding modes. Use in `arith.truncf` folding.
As this is not supported in dialects other than LLVM, conversion should fail for
now in case this attribute is present.
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Signed-off-by: Victor Perez <victor.perez@codeplay.com>
Many machine-learning applications (and most software written at AMD)
expect the operation that truncates floats to 8-bit floats to be
saturatinng. That is, they expect `truncf 256.0 : f32 to f8E4M3FNUZ` to
yield `240.0`, not `NaN`, and similarly for negative numbers. However,
the underlying hardware instruction that can be used for this truncation
implements overflow-to-NaN semantics.
To enable handling this usecase, we add the saturate-fp8-truncf option
to ArithToAMDGPU (off by default), which causes the requisite clamping
code to be emitted. Said clamping code ensures that Inf and NaN are
passed through exactly (and thus trancate to NaN).
Per review feedback, this commit efactors
createScalarOrSplatConstant() to the Arith dialect utilities and uses
it in this code. It also fixes naming of existing patterns and
switches from vector.extractelement/insertelement to
vector.extract/insert.
Define operations that wrap the gfx940's new operations for converting
between f32 and registers containing packed sets of four 8-bit floats.
Define rocdl operations for the intrinsics and an AMDGPU dialect
wrapper around them (to account for the fact that MLIR distinguishes
the two float formats at the type level but that the LLVM IR does
not).
Define an ArithToAMDGPU pass, meant to run before conversion to LLVM,
that replaces relevant calls to arith.extf and arith.truncf with the
packed operations in the AMDGPU dialect. Note that the conversion
currently only handles scalars and vectors of rank <= 1, as we do not
have a usecase for multi-dimensional vector support right now.
Reviewed By: jsjodin
Differential Revision: https://reviews.llvm.org/D152457
