Implement lowering of torch.aten.exponential (#2680)

https://github.com/llvm/torch-mlir/issues/2646

Decompose aten.exponential() into: -exp(1-x)/lambda

include/torch-mlir/Dialect/Torch/IR/GeneratedTorchOps.td

@@ -4739,6 +4739,31 @@ def Torch_AtenBernoulliPOp : Torch_Op<"aten.bernoulli.p", [
   }];
 }
 
+def Torch_AtenExponentialOp : Torch_Op<"aten.exponential", [
+    AllowsTypeRefinement,
+    HasValueSemantics,
+    ReadOnly
+  ]> {
+  let summary = "Generated op for `aten::exponential : (Tensor, float, Generator?) -> (Tensor)`";
+  let arguments = (ins
+    AnyTorchTensorType:$self,
+    Torch_FloatType:$lambd,
+    AnyTorchOptionalGeneratorType:$generator
+  );
+  let results = (outs
+    AnyTorchTensorType:$result
+  );
+  let hasCustomAssemblyFormat = 1;
+  let extraClassDefinition = [{
+    ParseResult AtenExponentialOp::parse(OpAsmParser &parser, OperationState &result) {
+      return parseDefaultTorchOp(parser, result, 3, 1);
+    }
+    void AtenExponentialOp::print(OpAsmPrinter &printer) {
+      printDefaultTorchOp(printer, *this, 3, 1);
+    }
+  }];
+}
+
 def Torch_AtenMultinomialOp : Torch_Op<"aten.multinomial", [
     AllowsTypeRefinement,
     HasValueSemantics,

lib/Dialect/Torch/Transforms/AbstractInterpLibrary.cpp

@@ -7580,6 +7580,9 @@ StringRef mlir::torch::Torch::getAbstractInterpLibrary() {
 "  func.func @\"__torch_mlir_shape_fn.aten.uniform\"(%arg0: !torch.list<int>, %arg1: !torch.float, %arg2: !torch.float, %arg3: !torch.any) -> !torch.list<int> {\n"
 "    return %arg0 : !torch.list<int>\n"
 "  }\n"
+"  func.func @\"__torch_mlir_shape_fn.aten.exponential\"(%arg0: !torch.list<int>, %arg1: !torch.float, %arg2: !torch.any) -> !torch.list<int> {\n"
+"    return %arg0 : !torch.list<int>\n"
+"  }\n"
 "  func.func @\"__torch_mlir_shape_fn.aten.rand\"(%arg0: !torch.list<int>, %arg1: !torch.optional<int>, %arg2: !torch.optional<int>, %arg3: !torch.optional<Device>, %arg4: !torch.optional<bool>) -> !torch.list<int> {\n"
 "    return %arg0 : !torch.list<int>\n"
 "  }\n"
@@ -9382,6 +9385,10 @@ StringRef mlir::torch::Torch::getAbstractInterpLibrary() {
 "    %0:2 = torch.prim.TupleUnpack %arg0 : !torch.tuple<int, int> -> !torch.int, !torch.int\n"
 "    return %0#1 : !torch.int\n"
 "  }\n"
+"  func.func @\"__torch_mlir_dtype_fn.aten.exponential\"(%arg0: !torch.tuple<int, int>, %arg1: !torch.float, %arg2: !torch.any) -> !torch.int {\n"
+"    %0:2 = torch.prim.TupleUnpack %arg0 : !torch.tuple<int, int> -> !torch.int, !torch.int\n"
+"    return %0#1 : !torch.int\n"
+"  }\n"
 "  func.func @\"__torch_mlir_dtype_fn.aten.rand\"(%arg0: !torch.list<int>, %arg1: !torch.optional<int>, %arg2: !torch.optional<int>, %arg3: !torch.optional<Device>, %arg4: !torch.optional<bool>) -> !torch.int {\n"
 "    %int6 = torch.constant.int 6\n"
 "    %none = torch.constant.none\n"

lib/Dialect/Torch/Transforms/DecomposeComplexOps.cpp

@@ -3562,6 +3562,51 @@ public:
 };
 } // namespace
 
+namespace {
+// Decompose exponential() to do inverse transform sampling.
+// - https://en.wikipedia.org/wiki/Inverse_transform_sampling
+// With the exponential distribution, F(x) = 1 - exp(-lambda * x). Thus,
+// exponential() = - ln(1 - uniform(0, 1)) / lambda.
+class DecomposeAtenExponentialOp : public OpRewritePattern<AtenExponentialOp> {
+public:
+  using OpRewritePattern::OpRewritePattern;
+  LogicalResult matchAndRewrite(AtenExponentialOp op,
+                                PatternRewriter &rewriter) const override {
+    if (!op.getGenerator().getType().isa<Torch::NoneType>())
+      return rewriter.notifyMatchFailure(
+          op, "The generator has to be None because only global default "
+              "generator is supported");
+
+    Location loc = op.getLoc();
+    Type resultType = op.getType();
+
+    // Create a uniform random op with low and high set to 0.0 and 1.0,
+    // respectively.
+    Value none = rewriter.create<ConstantNoneOp>(loc);
+    Value zero =
+        rewriter.create<ConstantFloatOp>(loc, rewriter.getF64FloatAttr(0.0));
+    Value one =
+        rewriter.create<ConstantFloatOp>(loc, rewriter.getF64FloatAttr(1.0));
+    Value emptyTensor = rewriter.create<AtenFullLikeOp>(
+        loc, resultType, op.getSelf(), zero, /*dtype=*/none, /*layout=*/none,
+        /*device=*/none, /*pin_memoty=*/none, /*memory_format=*/none);
+    Value x = rewriter.create<AtenUniformOp>(loc, resultType, emptyTensor,
+                                             /*from=*/zero, /*to=*/one,
+                                             /*generator=*/none);
+
+    Value negX = rewriter.create<AtenNegOp>(loc, resultType, x);
+    Value oneMinusX =
+        rewriter.create<AtenAddScalarOp>(loc, resultType, negX, one,
+                                         /*alpha=*/one);
+    Value lnOneMinusX = rewriter.create<AtenLogOp>(loc, resultType, oneMinusX);
+    Value negLambda = rewriter.create<AtenNegFloatOp>(loc, op.getLambd());
+    rewriter.replaceOpWithNewOp<AtenDivScalarOp>(op, resultType, lnOneMinusX,
+                                                 negLambda);
+    return success();
+  }
+};
+} // namespace
+
 namespace {
 template <typename OpTy, typename T1T2Op>
 class DecomposeAtenAddCLikeOp : public OpRewritePattern<OpTy> {
@@ -6410,6 +6455,7 @@ public:
     addPatternIfTargetOpIsIllegal<
         DecomposeAtenBernoulliLikeOp<AtenBernoulliPOp>>(patterns);
     addPatternIfTargetOpIsIllegal<DecomposeAtenBernoulliTensorOp>(patterns);
+    addPatternIfTargetOpIsIllegal<DecomposeAtenExponentialOp>(patterns);
     addPatternIfTargetOpIsIllegal<DecomposeAtenZeroOp>(patterns);
     addPatternIfTargetOpIsIllegal<DecomposeAtenEyeOp>(patterns);
     addPatternIfTargetOpIsIllegal<DecomposeAtenEyeMOp>(patterns);

lib/Dialect/Torch/Transforms/LowerToBackendContract.cpp

@@ -427,6 +427,7 @@ static void markDecomposedOpsAsIllegal(MLIRContext *context,
   target.addIllegalOp<ValsemVariantAtenBernoulliFloatOp>();
   target.addIllegalOp<AtenBernoulliPOp>();
   target.addIllegalOp<AtenBernoulliTensorOp>();
+  target.addIllegalOp<AtenExponentialOp>();
   target.addIllegalOp<AtenZeroOp>();
   target.addIllegalOp<AtenEyeOp>();
   target.addIllegalOp<AtenEyeMOp>();

projects/pt1/e2e_testing/xfail_sets.py

@@ -1397,6 +1397,7 @@ LTC_XFAIL_SET = {
     "CeilFloatModule_basic",
     "DivFloatModule_basic",
     "EqIntModule_basic",
+    "ExponentialModule_basic",
     "GeFloatIntModule_basic",
     "GeFloatModule_basic",
     "GeIntModule_basic",

projects/pt1/python/torch_mlir/jit_ir_importer/build_tools/abstract_interp_lib_gen.py

@@ -831,6 +831,9 @@ def aten〇copy〡shape(self: List[int], src: List[int], non_blocking: bool = Fa
 def aten〇uniform〡shape(self: List[int], from_: float = 0., to: float = 1., generator: Any = None) -> List[int]:
     return self
 
+def aten〇exponential〡shape(self: List[int], lambd: float = 1., generator: Any = None) -> List[int]:
+    return self
+
 def aten〇rand〡shape(size: List[int], dtype: Optional[int] = None, layout: Optional[int] = None, device: Optional[device] = None, pin_memory: Optional[bool] = None) -> List[int]:
     return size
 
@@ -2267,6 +2270,10 @@ def aten〇uniform〡dtype(self_rank_dtype: Tuple[int, int], from_: float = 0.,
     self_rank, self_dtype = self_rank_dtype
     return self_dtype
 
+def aten〇exponential〡dtype(self_rank_dtype: Tuple[int, int], lambd: float = 1., generator: Any = None) -> int:
+    self_rank, self_dtype = self_rank_dtype
+    return self_dtype
+
 @check_dtype_function([Invocation([1]),
                        Invocation([1], dtype=torch.float16),
                        Invocation([1], dtype=torch.complex64)])

projects/pt1/python/torch_mlir/jit_ir_importer/build_tools/torch_ods_gen.py

@@ -378,6 +378,7 @@ def emit_ops(emitter_td: TextEmitter, registry: Registry):
     emit("aten::bernoulli : (Tensor, Generator?) -> (Tensor)")
     emit("aten::bernoulli_.float : (Tensor, float, Generator?) -> (Tensor)")
     emit("aten::bernoulli.p : (Tensor, float, Generator?) -> (Tensor)")
+    emit("aten::exponential : (Tensor, float, Generator?) -> (Tensor)")
     emit("aten::multinomial : (Tensor, int, bool, Generator?) -> (Tensor)")
     emit("aten::randint.low : (int, int, int[], int?, int?, Device?, bool?) -> (Tensor)")
     emit("aten::randint : (int, int[], int?, int?, Device?, bool?) -> (Tensor)")

projects/pt1/python/torch_mlir_e2e_test/test_suite/rng.py

@@ -157,6 +157,29 @@ def UniformNoCorrelationModule_basic(module, tu: TestUtils):
 
 # ==============================================================================
 
+class ExponentialModule(torch.nn.Module):
+    def __init__(self):
+        super().__init__()
+
+    @export
+    @annotate_args([
+        None,
+        ([-1, -1, -1], torch.float64, True),
+    ])
+    def forward(self, x):
+        a = torch.ops.aten.exponential(x, 3.0)
+        mean = torch.mean(a)
+        std = torch.std(a)
+        return  mean, std
+
+
+@register_test_case(module_factory=lambda: ExponentialModule())
+def ExponentialModule_basic(module, tu: TestUtils):
+    module.forward(
+        tu.rand(512, 512, 16).double())
+
+# ==============================================================================
+
 class BernoulliModule(torch.nn.Module):
     def __init__(self):
         super().__init__()