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[FXML-2939] Fix rsqrt folder for bfloat16 #81

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Sep 14, 2023
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[FXML-2939] Fix rsqrt folder for bfloat16 #81

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7 changes: 6 additions & 1 deletion mlir/lib/Dialect/Tosa/Transforms/TosaFolders.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -590,6 +590,11 @@ struct TosaFoldConstantRSQRT
auto floatVal = apFloatVal.convertToFloat();
auto sqrtVal = std::sqrt(floatVal);
APFloat apSqrtVal(sqrtVal);
// We fold only float32 and bfloat16, so we do not expect any precision loss
// for float32 and the tosa spec explicitly allows to implement bfloat16 as
// float32, so any precision loss on the conversion back is fine.
bool losesInfo = false;
apSqrtVal.convert(apFloatVal.getSemantics(), tosaRoundingMode, &losesInfo);

// Compute the reciprocal
return computeReciprocal(apSqrtVal, floatTy);
Expand All @@ -602,7 +607,7 @@ struct TosaFoldConstantRSQRT
}

bool isSupportedElementType(Type type) const {
return type.isBF16() || type.isF16() || type.isF32();
return type.isBF16() || type.isF32();
}
};

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10 changes: 10 additions & 0 deletions mlir/test/Dialect/Tosa/constant-rsqrt-opt.mlir
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Expand Up @@ -123,6 +123,16 @@ func.func @rsqrt_fold() -> tensor<4x6xf32> {
return %1 : tensor<4x6xf32>
}

// CHECK-LABEL: @rsqrt_fold_single_valued_bf16
func.func @rsqrt_fold_single_valued_bf16() -> tensor<bf16> {
// CHECK: [[RES:]] ={{.*}}tosa.const{{.*}}2.890630e-01{{.*}}tensor<bf16>
// CHECK-NOT: tosa.rsqrt
// CHECK: return [[RES]]
%0 = "tosa.const"() {value = dense<12.0> : tensor<bf16>} : () -> tensor<bf16>
%1 = "tosa.rsqrt"(%0) : (tensor<bf16>) -> tensor<bf16>
return %1 : tensor<bf16>
}

// CHECK-LABEL: @rsqrt_of_const_sparse
// Sparse tensors are currently not supported
func.func @rsqrt_of_const_sparse() -> tensor<32xbf16> {
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