//===- SCFOps.td - Structured Control Flow operations ------*- tablegen -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// Defines MLIR structured control flow operations.
//
//===----------------------------------------------------------------------===//
#ifndef MLIR_DIALECT_SCF_SCFOPS
#define MLIR_DIALECT_SCF_SCFOPS
include "mlir/Interfaces/ControlFlowInterfaces.td"
include "mlir/Interfaces/LoopLikeInterface.td"
include "mlir/IR/RegionKindInterface.td"
include "mlir/Dialect/SCF/IR/DeviceMappingInterface.td"
include "mlir/Interfaces/DestinationStyleOpInterface.td"
include "mlir/Interfaces/InferTypeOpInterface.td"
include "mlir/Interfaces/ParallelCombiningOpInterface.td"
include "mlir/Interfaces/SideEffectInterfaces.td"
include "mlir/Interfaces/ViewLikeInterface.td"
def SCF_Dialect : Dialect {
let name = "scf";
let cppNamespace = "::mlir::scf";
let description = [{
The `scf` (structured control flow) dialect contains operations that
represent control flow constructs such as `if` and `for`. Being
_structured_ means that the control flow has a structure unlike, for
example, `goto`s or `assert`s. Unstructured control flow operations are
located in the `cf` (control flow) dialect.
Originally, this dialect was developed as a common lowering stage for the
`affine` and `linalg` dialects. Both convert to SCF loops instead of
targeting branch-based CFGs directly. Typically, `scf` is lowered to `cf`
and then lowered to some final target like LLVM or SPIR-V.
}];
let dependentDialects = ["arith::ArithDialect"];
}
// Base class for SCF dialect ops.
class SCF_Op<string mnemonic, list<Trait> traits = []> :
Op<SCF_Dialect, mnemonic, traits>;
//===----------------------------------------------------------------------===//
// ConditionOp
//===----------------------------------------------------------------------===//
def ConditionOp : SCF_Op<"condition", [
HasParent<"WhileOp">,
DeclareOpInterfaceMethods<RegionBranchTerminatorOpInterface,
["getSuccessorRegions"]>,
Pure,
Terminator
]> {
let summary = "loop continuation condition";
let description = [{
This operation accepts the continuation (i.e., inverse of exit) condition
of the `scf.while` construct. If its first argument is true, the "after"
region of `scf.while` is executed, with the remaining arguments forwarded
to the entry block of the region. Otherwise, the loop terminates.
}];
let arguments = (ins I1:$condition, Variadic<AnyType>:$args);
let assemblyFormat =
[{ `(` $condition `)` attr-dict ($args^ `:` type($args))? }];
}
//===----------------------------------------------------------------------===//
// ExecuteRegionOp
//===----------------------------------------------------------------------===//
def ExecuteRegionOp : SCF_Op<"execute_region", [
DeclareOpInterfaceMethods<RegionBranchOpInterface>]> {
let summary = "operation that executes its region exactly once";
let description = [{
The `scf.execute_region` operation is used to allow multiple blocks within SCF
and other operations which can hold only one block. The `scf.execute_region`
operation executes the region held exactly once and cannot have any operands.
As such, its region has no arguments. All SSA values that dominate the op can
be accessed inside the op. The op's region can have multiple blocks and the
blocks can have multiple distinct terminators. Values returned from this op's
region define the op's results.
Example:
```mlir
scf.for %i = 0 to 128 step %c1 {
%y = scf.execute_region -> i32 {
%x = load %A[%i] : memref<128xi32>
scf.yield %x : i32
}
}
affine.for %i = 0 to 100 {
"foo"() : () -> ()
%v = scf.execute_region -> i64 {
cf.cond_br %cond, ^bb1, ^bb2
^bb1:
%c1 = arith.constant 1 : i64
cf.br ^bb3(%c1 : i64)
^bb2:
%c2 = arith.constant 2 : i64
cf.br ^bb3(%c2 : i64)
^bb3(%x : i64):
scf.yield %x : i64
}
"bar"(%v) : (i64) -> ()
}
```
}];
let results = (outs Variadic<AnyType>);
let regions = (region AnyRegion:$region);
let hasCanonicalizer = 1;
let hasCustomAssemblyFormat = 1;
let hasVerifier = 1;
}
//===----------------------------------------------------------------------===//
// ForOp
//===----------------------------------------------------------------------===//
def ForOp : SCF_Op<"for",
[AutomaticAllocationScope, DeclareOpInterfaceMethods<LoopLikeOpInterface,
["getInitsMutable", "getLoopResults", "getRegionIterArgs",
"getLoopInductionVars", "getLoopLowerBounds", "getLoopSteps",
"getLoopUpperBounds", "getYieldedValuesMutable",
"promoteIfSingleIteration", "replaceWithAdditionalYields",
"yieldTiledValuesAndReplace"]>,
AllTypesMatch<["lowerBound", "upperBound", "step"]>,
ConditionallySpeculatable,
DeclareOpInterfaceMethods<RegionBranchOpInterface,
["getEntrySuccessorOperands"]>,
SingleBlockImplicitTerminator<"scf::YieldOp">,
RecursiveMemoryEffects]> {
let summary = "for operation";
let description = [{
The `scf.for` operation represents a loop taking 3 SSA value as operands
that represent the lower bound, upper bound and step respectively. The
operation defines an SSA value for its induction variable. It has one
region capturing the loop body. The induction variable is represented as an
argument of this region. This SSA value is a signless integer or index.
The step is a value of same type but required to be positive. The lower and
upper bounds specify a half-open range: the range includes the lower bound
but does not include the upper bound.
The body region must contain exactly one block that terminates with
`scf.yield`. Calling ForOp::build will create such a region and insert
the terminator implicitly if none is defined, so will the parsing even in
cases when it is absent from the custom format. For example:
```mlir
// Index case.
scf.for %iv = %lb to %ub step %step {
... // body
}
...
// Integer case.
scf.for %iv_32 = %lb_32 to %ub_32 step %step_32 : i32 {
... // body
}
```
`scf.for` can also operate on loop-carried variables and returns the final
values after loop termination. The initial values of the variables are
passed as additional SSA operands to the `scf.for` following the 3 loop
control SSA values mentioned above (lower bound, upper bound and step). The
operation region has an argument for the induction variable, followed by
one argument for each loop-carried variable, representing the value of the
variable at the current iteration.
The region must terminate with a `scf.yield` that passes the current
values of all loop-carried variables to the next iteration, or to the
`scf.for` result, if at the last iteration. The static type of a
loop-carried variable may not change with iterations; its runtime type is
allowed to change. Note, that when the loop-carried variables are present,
calling ForOp::build will not insert the terminator implicitly. The caller
must insert `scf.yield` in that case.
`scf.for` results hold the final values after the last iteration.
For example, to sum-reduce a memref:
```mlir
func.func @reduce(%buffer: memref<1024xf32>, %lb: index,
%ub: index, %step: index) -> (f32) {
// Initial sum set to 0.
%sum_0 = arith.constant 0.0 : f32
// iter_args binds initial values to the loop's region arguments.
%sum = scf.for %iv = %lb to %ub step %step
iter_args(%sum_iter = %sum_0) -> (f32) {
%t = load %buffer[%iv] : memref<1024xf32>
%sum_next = arith.addf %sum_iter, %t : f32
// Yield current iteration sum to next iteration %sum_iter or to %sum
// if final iteration.
scf.yield %sum_next : f32
}
return %sum : f32
}
```
If the `scf.for` defines any values, a yield must be explicitly present.
The number and types of the `scf.for` results must match the initial
values in the `iter_args` binding and the yield operands.
Another example with a nested `scf.if` (see `scf.if` for details) to
perform conditional reduction:
```mlir
func.func @conditional_reduce(%buffer: memref<1024xf32>, %lb: index,
%ub: index, %step: index) -> (f32) {
%sum_0 = arith.constant 0.0 : f32
%c0 = arith.constant 0.0 : f32
%sum = scf.for %iv = %lb to %ub step %step
iter_args(%sum_iter = %sum_0) -> (f32) {
%t = load %buffer[%iv] : memref<1024xf32>
%cond = arith.cmpf "ugt", %t, %c0 : f32
%sum_next = scf.if %cond -> (f32) {
%new_sum = arith.addf %sum_iter, %t : f32
scf.yield %new_sum : f32
} else {
scf.yield %sum_iter : f32
}
scf.yield %sum_next : f32
}
return %sum : f32
}
```
}];
let arguments = (ins AnySignlessIntegerOrIndex:$lowerBound,
AnySignlessIntegerOrIndex:$upperBound,
AnySignlessIntegerOrIndex:$step,
Variadic<AnyType>:$initArgs);
let results = (outs Variadic<AnyType>:$results);
let regions = (region SizedRegion<1>:$region);
let skipDefaultBuilders = 1;
let builders = [
OpBuilder<(ins "Value":$lowerBound, "Value":$upperBound, "Value":$step,
CArg<"ValueRange", "std::nullopt">:$initArgs,
CArg<"function_ref<void(OpBuilder &, Location, Value, ValueRange)>",
"nullptr">)>
];
let extraClassDeclaration = [{
using BodyBuilderFn =
function_ref<void(OpBuilder &, Location, Value, ValueRange)>;
Value getInductionVar() { return getBody()->getArgument(0); }
/// Return the `index`-th region iteration argument.
BlockArgument getRegionIterArg(unsigned index) {
assert(index < getNumRegionIterArgs() &&
"expected an index less than the number of region iter args");
return getBody()->getArguments().drop_front(getNumInductionVars())[index];
}
void setLowerBound(Value bound) { getOperation()->setOperand(0, bound); }
void setUpperBound(Value bound) { getOperation()->setOperand(1, bound); }
void setStep(Value step) { getOperation()->setOperand(2, step); }
/// Number of induction variables, always 1 for scf::ForOp.
unsigned getNumInductionVars() { return 1; }
/// Number of region arguments for loop-carried values
unsigned getNumRegionIterArgs() {
return getBody()->getNumArguments() - getNumInductionVars();
}
/// Number of operands controlling the loop: lb, ub, step
unsigned getNumControlOperands() { return 3; }
/// Returns the step as an `APInt` if it is constant.
std::optional<APInt> getConstantStep();
/// Interface method for ConditionallySpeculatable.
Speculation::Speculatability getSpeculatability();
}];
let hasCanonicalizer = 1;
let hasCustomAssemblyFormat = 1;
let hasVerifier = 1;
let hasRegionVerifier = 1;
}
//===----------------------------------------------------------------------===//
// ForallOp
//===----------------------------------------------------------------------===//
def ForallOp : SCF_Op<"forall", [
AttrSizedOperandSegments,
AutomaticAllocationScope,
DeclareOpInterfaceMethods<LoopLikeOpInterface,
["getInitsMutable", "getRegionIterArgs", "getLoopInductionVars",
"getLoopLowerBounds", "getLoopUpperBounds", "getLoopSteps",
"promoteIfSingleIteration", "yieldTiledValuesAndReplace"]>,
RecursiveMemoryEffects,
SingleBlockImplicitTerminator<"scf::InParallelOp">,
DeclareOpInterfaceMethods<RegionBranchOpInterface>,
DestinationStyleOpInterface,
HasParallelRegion
]> {
let summary = "evaluate a block multiple times in parallel";
let description = [{
`scf.forall` is a target-independent multi-dimensional parallel
region application operation. It has exactly one block that represents the
parallel body and it takes index operands that specify lower bounds, upper
bounds and steps.
The op also takes a variadic number of tensor operands (`shared_outs`).
The future buffers corresponding to these tensors are shared among all
threads. Shared tensors should be accessed via their corresponding block
arguments. If multiple threads write to a shared buffer in a racy
fashion, these writes will execute in some unspecified order. Tensors that
are not shared can be used inside the body (i.e., the op is not isolated
from above); however, if a use of such a tensor bufferizes to a memory
write, the tensor is privatized, i.e., a thread-local copy of the tensor is
used. This ensures that memory side effects of a thread are not visible to
other threads (or in the parent body), apart from explicitly shared tensors.
The name "thread" conveys the fact that the parallel execution is mapped
(i.e. distributed) to a set of virtual threads of execution, one function
application per thread. Further lowerings are responsible for specifying
how this is materialized on concrete hardware resources.
An optional `mapping` is an attribute array that specifies processing units
with their dimension, how it remaps 1-1 to a set of concrete processing
element resources (e.g. a CUDA grid dimension or a level of concrete nested
async parallelism). It is expressed via any attribute that implements the
device mapping interface. It is the reponsibility of the lowering mechanism
to interpret the `mapping` attributes in the context of the concrete target
the op is lowered to, or to ignore it when the specification is ill-formed
or unsupported for a particular target.
The only allowed terminator is `scf.forall.in_parallel`.
`scf.forall` returns one value per `shared_out` operand. The
actions of the `scf.forall.in_parallel` terminators specify how to combine the
partial results of all parallel invocations into a full value, in some
unspecified order. The "destination" of each such op must be a `shared_out`
block argument of the `scf.forall` op.
The actions involved in constructing the return values are further described
by `tensor.parallel_insert_slice`.
`scf.forall` acts as an implicit synchronization point.
When the parallel function body has side effects, their order is unspecified
across threads.
`scf.forall` can be printed in two different ways depending on
whether the loop is normalized or not. The loop is 'normalized' when all
lower bounds are equal to zero and steps are equal to one. In that case,
`lowerBound` and `step` operands will be omitted during printing.
Normalized loop example:
```mlir
//
// Sequential context.
//
%matmul_and_pointwise:2 = scf.forall (%thread_id_1, %thread_id_2) in
(%num_threads_1, %numthread_id_2) shared_outs(%o1 = %C, %o2 = %pointwise)
-> (tensor<?x?xT>, tensor<?xT>) {
//
// Parallel context, each thread with id = (%thread_id_1, %thread_id_2)
// runs its version of the code.
//
%sA = tensor.extract_slice %A[f((%thread_id_1, %thread_id_2))]:
tensor<?x?xT> to tensor<?x?xT>
%sB = tensor.extract_slice %B[g((%thread_id_1, %thread_id_2))]:
tensor<?x?xT> to tensor<?x?xT>
%sC = tensor.extract_slice %o1[h((%thread_id_1, %thread_id_2))]:
tensor<?x?xT> to tensor<?x?xT>
%sD = linalg.matmul
ins(%sA, %sB : tensor<?x?xT>, tensor<?x?xT>)
outs(%sC : tensor<?x?xT>)
%spointwise = subtensor %o2[i((%thread_id_1, %thread_id_2))]:
tensor<?xT> to tensor<?xT>
%sE = linalg.add ins(%spointwise : tensor<?xT>) outs(%sD : tensor<?xT>)
scf.forall.in_parallel {
tensor.parallel_insert_slice %sD into %o1[h((%thread_id_1, %thread_id_2))]:
tensor<?x?xT> into tensor<?x?xT>
tensor.parallel_insert_slice %spointwise into %o2[i((%thread_id_1, %thread_id_2))]:
tensor<?xT> into tensor<?xT>
}
}
// Implicit synchronization point.
// Sequential context.
//
```
Loop with loop bounds example:
```mlir
//
// Sequential context.
//
%pointwise = scf.forall (%i, %j) = (0, 0) to (%dim1, %dim2)
step (%tileSize1, %tileSize2) shared_outs(%o1 = %out)
-> (tensor<?x?xT>, tensor<?xT>) {
//
// Parallel context.
//
%sA = tensor.extract_slice %A[%i, %j][%tileSize1, %tileSize2][1, 1]
: tensor<?x?xT> to tensor<?x?xT>
%sB = tensor.extract_slice %B[%i, %j][%tileSize1, %tileSize2][1, 1]
: tensor<?x?xT> to tensor<?x?xT>
%sC = tensor.extract_slice %o[%i, %j][%tileSize1, %tileSize2][1, 1]
: tensor<?x?xT> to tensor<?x?xT>
%add = linalg.map {"arith.addf"}
ins(%sA, %sB : tensor<?x?xT>, tensor<?x?xT>)
outs(%sC : tensor<?x?xT>)
scf.forall.in_parallel {
tensor.parallel_insert_slice %add into
%o[%i, %j][%tileSize1, %tileSize2][1, 1]
: tensor<?x?xT> into tensor<?x?xT>
}
}
// Implicit synchronization point.
// Sequential context.
//
```
Example with mapping attribute:
```mlir
//
// Sequential context. Here `mapping` is expressed as GPU thread mapping
// attributes
//
%matmul_and_pointwise:2 = scf.forall (%thread_id_1, %thread_id_2) in
(%num_threads_1, %numthread_id_2) shared_outs(...)
-> (tensor<?x?xT>, tensor<?xT>) {
//
// Parallel context, each thread with id = **(%thread_id_2, %thread_id_1)**
// runs its version of the code.
//
scf.forall.in_parallel {
...
}
} { mapping = [#gpu.thread<y>, #gpu.thread<x>] }
// Implicit synchronization point.
// Sequential context.
//
```
Example with privatized tensors:
```mlir
%t0 = ...
%t1 = ...
%r = scf.forall ... shared_outs(%o = t0) -> tensor<?xf32> {
// %t0 and %t1 are privatized. %t0 is definitely copied for each thread
// because the scf.forall op's %t0 use bufferizes to a memory
// write. In the absence of other conflicts, %t1 is copied only if there
// are uses of %t1 in the body that bufferize to a memory read and to a
// memory write.
"some_use"(%t0)
"some_use"(%t1)
}
```
}];
let arguments = (ins
Variadic<Index>:$dynamicLowerBound,
Variadic<Index>:$dynamicUpperBound,
Variadic<Index>:$dynamicStep,
DenseI64ArrayAttr:$staticLowerBound,
DenseI64ArrayAttr:$staticUpperBound,
DenseI64ArrayAttr:$staticStep,
Variadic<AnyRankedTensor>:$outputs,
OptionalAttr<DeviceMappingArrayAttr>:$mapping);
let results = (outs Variadic<AnyType>:$results);
let regions = (region SizedRegion<1>:$region);
let hasCanonicalizer = 1;
let hasCustomAssemblyFormat = 1;
let hasVerifier = 1;
// The default builder does not add the proper body BBargs, roll our own.
let skipDefaultBuilders = 1;
let builders = [
// Builder that takes loop bounds.
OpBuilder<(ins "ArrayRef<OpFoldResult>":$lbs,
"ArrayRef<OpFoldResult>":$ubs, "ArrayRef<OpFoldResult>":$steps,
"ValueRange":$outputs, "std::optional<ArrayAttr>":$mapping,
CArg<"function_ref<void(OpBuilder &, Location, ValueRange)>",
"nullptr"> :$bodyBuilderFn)>,
// Builder for normalized loop that takes only upper bounds.
OpBuilder<(ins "ArrayRef<OpFoldResult>":$ubs,
"ValueRange":$outputs, "std::optional<ArrayAttr>":$mapping,
CArg<"function_ref<void(OpBuilder &, Location, ValueRange)>",
"nullptr"> :$bodyBuilderFn)>,
];
let extraClassDeclaration = [{
/// Get induction variables.
SmallVector<Value> getInductionVars() {
std::optional<SmallVector<Value>> maybeInductionVars = getLoopInductionVars();
assert(maybeInductionVars.has_value() && "expected values");
return *maybeInductionVars;
}
/// Get lower bounds as OpFoldResult.
SmallVector<OpFoldResult> getMixedLowerBound() {
std::optional<SmallVector<OpFoldResult>> maybeLowerBounds = getLoopLowerBounds();
assert(maybeLowerBounds.has_value() && "expected values");
return *maybeLowerBounds;
}
/// Get upper bounds as OpFoldResult.
SmallVector<OpFoldResult> getMixedUpperBound() {
std::optional<SmallVector<OpFoldResult>> maybeUpperBounds = getLoopUpperBounds();
assert(maybeUpperBounds.has_value() && "expected values");
return *maybeUpperBounds;
}
/// Get steps as OpFoldResult.
SmallVector<OpFoldResult> getMixedStep() {
std::optional<SmallVector<OpFoldResult>> maybeSteps = getLoopSteps();
assert(maybeSteps.has_value() && "expected values");
return *maybeSteps;
}
/// Get lower bounds as values.
SmallVector<Value> getLowerBound(OpBuilder &b) {
return getValueOrCreateConstantIndexOp(b, getLoc(), getMixedLowerBound());
}
/// Get upper bounds as values.
SmallVector<Value> getUpperBound(OpBuilder &b) {
return getValueOrCreateConstantIndexOp(b, getLoc(), getMixedUpperBound());
}
/// Get steps as values.
SmallVector<Value> getStep(OpBuilder &b) {
return getValueOrCreateConstantIndexOp(b, getLoc(), getMixedStep());
}
int64_t getRank() { return getStaticLowerBound().size(); }
/// Number of operands controlling the loop: lbs, ubs, steps
unsigned getNumControlOperands() { return 3 * getRank(); }
/// Number of dynamic operands controlling the loop: lbs, ubs, steps
unsigned getNumDynamicControlOperands() {
return getODSOperandIndexAndLength(3).first;
}
OpResult getTiedOpResult(OpOperand *opOperand) {
assert(opOperand->getOperandNumber() >= getNumDynamicControlOperands() &&
"invalid operand");
return getOperation()->getOpResult(
opOperand->getOperandNumber() - getNumDynamicControlOperands());
}
/// Return the num_threads operand that is tied to the given thread id
/// block argument.
OpOperand *getTiedOpOperand(BlockArgument bbArg) {
assert(bbArg.getArgNumber() >= getRank() && "invalid bbArg");
return &getOperation()->getOpOperand(getNumDynamicControlOperands() +
bbArg.getArgNumber() - getRank());
}
/// Return the shared_outs operand that is tied to the given OpResult.
OpOperand *getTiedOpOperand(OpResult opResult) {
assert(opResult.getDefiningOp() == getOperation() && "invalid OpResult");
return &getOperation()->getOpOperand(getNumDynamicControlOperands() +
opResult.getResultNumber());
}
BlockArgument getTiedBlockArgument(OpOperand *opOperand) {
assert(opOperand->getOperandNumber() >= getNumDynamicControlOperands() &&
"invalid operand");
return getBody()->getArgument(opOperand->getOperandNumber() -
getNumDynamicControlOperands() + getRank());
}
::mlir::Value getInductionVar(int64_t idx) {
return getInductionVars()[idx];
}
::mlir::Block::BlockArgListType getRegionOutArgs() {
return getBody()->getArguments().drop_front(getRank());
}
/// Checks if the lbs are zeros and steps are ones.
bool isNormalized();
// The ensureTerminator method generated by SingleBlockImplicitTerminator is
// unaware of the fact that our terminator also needs a region to be
// well-formed. We override it here to ensure that we do the right thing.
static void ensureTerminator(Region & region, OpBuilder & builder,
Location loc);
InParallelOp getTerminator();
// Declare the shared_outs as inits/outs to DestinationStyleOpInterface.
MutableOperandRange getDpsInitsMutable() { return getOutputsMutable(); }
/// Returns operations within scf.forall.in_parallel whose destination
/// operand is the block argument `bbArg`.
SmallVector<Operation*> getCombiningOps(BlockArgument bbArg);
}];
}
//===----------------------------------------------------------------------===//
// InParallelOp
//===----------------------------------------------------------------------===//
def InParallelOp : SCF_Op<"forall.in_parallel", [
Pure,
Terminator,
DeclareOpInterfaceMethods<ParallelCombiningOpInterface>,
HasParent<"ForallOp">,
] # GraphRegionNoTerminator.traits> {
let summary = "terminates a `forall` block";
let description = [{
The `scf.forall.in_parallel` is a designated terminator for
the `scf.forall` operation.
It has a single region with a single block that contains a flat list of ops.
Each such op participates in the aggregate formation of a single result of
the enclosing `scf.forall`.
The result number corresponds to the position of the op in the terminator.
}];
let regions = (region SizedRegion<1>:$region);
let hasCustomAssemblyFormat = 1;
let hasVerifier = 1;
// The default builder does not add a region with an empty body, add our own.
let skipDefaultBuilders = 1;
let builders = [
OpBuilder<(ins)>,
];
// TODO: Add a `InParallelOpInterface` interface for ops that can
// appear inside in_parallel.
let extraClassDeclaration = [{
::llvm::SmallVector<::mlir::BlockArgument> getDests();
::llvm::iterator_range<::mlir::Block::iterator> getYieldingOps();
::mlir::OpResult getParentResult(int64_t idx);
}];
}
//===----------------------------------------------------------------------===//
// IfOp
//===----------------------------------------------------------------------===//
def IfOp : SCF_Op<"if", [DeclareOpInterfaceMethods<RegionBranchOpInterface, [
"getNumRegionInvocations", "getRegionInvocationBounds",
"getEntrySuccessorRegions"]>,
InferTypeOpAdaptor, SingleBlockImplicitTerminator<"scf::YieldOp">,
RecursiveMemoryEffects, NoRegionArguments]> {
let summary = "if-then-else operation";
let description = [{
The `scf.if` operation represents an if-then-else construct for
conditionally executing two regions of code. The operand to an if operation
is a boolean value. For example:
```mlir
scf.if %b {
...
} else {
...
}
```
`scf.if` may also produce results. Which values are returned depends on
which execution path is taken.
Example:
```mlir
%x, %y = scf.if %b -> (f32, f32) {
%x_true = ...
%y_true = ...
scf.yield %x_true, %y_true : f32, f32
} else {
%x_false = ...
%y_false = ...
scf.yield %x_false, %y_false : f32, f32
}
```
The "then" region has exactly 1 block. The "else" region may have 0 or 1
block. In case the `scf.if` produces results, the "else" region must also
have exactly 1 block.
The blocks are always terminated with `scf.yield`. If `scf.if` defines no
values, the `scf.yield` can be left out, and will be inserted implicitly.
Otherwise, it must be explicit.
Example:
```mlir
scf.if %b {
...
}
```
The types of the yielded values must match the result types of the
`scf.if`.
}];
let arguments = (ins I1:$condition);
let results = (outs Variadic<AnyType>:$results);
let regions = (region SizedRegion<1>:$thenRegion,
MaxSizedRegion<1>:$elseRegion);
let skipDefaultBuilders = 1;
let builders = [
OpBuilder<(ins "TypeRange":$resultTypes, "Value":$cond)>,
OpBuilder<(ins "TypeRange":$resultTypes, "Value":$cond,
"bool":$addThenBlock, "bool":$addElseBlock)>,
OpBuilder<(ins "Value":$cond, "bool":$withElseRegion)>,
OpBuilder<(ins "TypeRange":$resultTypes, "Value":$cond,
"bool":$withElseRegion)>,
OpBuilder<(ins "Value":$cond,
CArg<"function_ref<void(OpBuilder &, Location)>",
"buildTerminatedBody">:$thenBuilder,
CArg<"function_ref<void(OpBuilder &, Location)>",
"nullptr">:$elseBuilder)>,
];
let extraClassDeclaration = [{
OpBuilder getThenBodyBuilder(OpBuilder::Listener *listener = nullptr) {
Block* body = getBody(0);
return getResults().empty() ? OpBuilder::atBlockTerminator(body, listener)
: OpBuilder::atBlockEnd(body, listener);
}
OpBuilder getElseBodyBuilder(OpBuilder::Listener *listener = nullptr) {
Block* body = getBody(1);
return getResults().empty() ? OpBuilder::atBlockTerminator(body, listener)
: OpBuilder::atBlockEnd(body, listener);
}
Block* thenBlock();
YieldOp thenYield();
Block* elseBlock();
YieldOp elseYield();
}];
let hasFolder = 1;
let hasCanonicalizer = 1;
let hasCustomAssemblyFormat = 1;
let hasVerifier = 1;
}
//===----------------------------------------------------------------------===//
// ParallelOp
//===----------------------------------------------------------------------===//
def ParallelOp : SCF_Op<"parallel",
[AutomaticAllocationScope,
AttrSizedOperandSegments,
DeclareOpInterfaceMethods<LoopLikeOpInterface, ["getLoopInductionVars",
"getLoopLowerBounds", "getLoopUpperBounds", "getLoopSteps"]>,
RecursiveMemoryEffects,
DeclareOpInterfaceMethods<RegionBranchOpInterface>,
SingleBlockImplicitTerminator<"scf::ReduceOp">,
HasParallelRegion]> {
let summary = "parallel for operation";
let description = [{
The `scf.parallel` operation represents a loop nest taking 4 groups of SSA
values as operands that represent the lower bounds, upper bounds, steps and
initial values, respectively. The operation defines a variadic number of
SSA values for its induction variables. It has one region capturing the
loop body. The induction variables are represented as an argument of this
region. These SSA values always have type index, which is the size of the
machine word. The steps are values of type index, required to be positive.
The lower and upper bounds specify a half-open range: the range includes
the lower bound but does not include the upper bound. The initial values
have the same types as results of `scf.parallel`. If there are no results,
the keyword `init` can be omitted.
Semantically we require that the iteration space can be iterated in any
order, and the loop body can be executed in parallel. If there are data
races, the behavior is undefined.
The parallel loop operation supports reduction of values produced by
individual iterations into a single result. This is modeled using the
`scf.reduce` terminator operation (see `scf.reduce` for details). The i-th
result of an `scf.parallel` operation is associated with the i-th initial
value operand, the i-th operand of the `scf.reduce` operation (the value to
be reduced) and the i-th region of the `scf.reduce` operation (the reduction
function). Consequently, we require that the number of results of an
`scf.parallel` op matches the number of initial values and the the number of
reductions in the `scf.reduce` terminator.
The body region must contain exactly one block that terminates with a
`scf.reduce` operation. If an `scf.parallel` op has no reductions, the
terminator has no operands and no regions. The `scf.parallel` parser will
automatically insert the terminator for ops that have no reductions if it is
absent.
Example:
```mlir
%init = arith.constant 0.0 : f32
%r:2 = scf.parallel (%iv) = (%lb) to (%ub) step (%step) init (%init, %init)
-> f32, f32 {
%elem_to_reduce1 = load %buffer1[%iv] : memref<100xf32>
%elem_to_reduce2 = load %buffer2[%iv] : memref<100xf32>
scf.reduce(%elem_to_reduce1, %elem_to_reduce2 : f32, f32) {
^bb0(%lhs : f32, %rhs: f32):
%res = arith.addf %lhs, %rhs : f32
scf.reduce.return %res : f32
}, {
^bb0(%lhs : f32, %rhs: f32):
%res = arith.mulf %lhs, %rhs : f32
scf.reduce.return %res : f32
}
}
```
}];
let arguments = (ins Variadic<Index>:$lowerBound,
Variadic<Index>:$upperBound,
Variadic<Index>:$step,
Variadic<AnyType>:$initVals);
let results = (outs Variadic<AnyType>:$results);
let regions = (region SizedRegion<1>:$region);
let skipDefaultBuilders = 1;
let builders = [
OpBuilder<(ins "ValueRange":$lowerBounds, "ValueRange":$upperBounds,
"ValueRange":$steps, "ValueRange":$initVals,
CArg<"function_ref<void (OpBuilder &, Location, ValueRange, ValueRange)>",
"nullptr">:$bodyBuilderFn)>,
OpBuilder<(ins "ValueRange":$lowerBounds, "ValueRange":$upperBounds,
"ValueRange":$steps,
CArg<"function_ref<void (OpBuilder &, Location, ValueRange)>",
"nullptr">:$bodyBuilderFn)>,
];
let extraClassDeclaration = [{
/// Get induction variables.
SmallVector<Value> getInductionVars() {
std::optional<SmallVector<Value>> maybeInductionVars = getLoopInductionVars();;
assert(maybeInductionVars.has_value() && "expected values");
return *maybeInductionVars;
}
unsigned getNumLoops() { return getStep().size(); }
unsigned getNumReductions() { return getInitVals().size(); }
}];
let hasCanonicalizer = 1;
let hasCustomAssemblyFormat = 1;
let hasVerifier = 1;
}
//===----------------------------------------------------------------------===//
// ReduceOp
//===----------------------------------------------------------------------===//
def ReduceOp : SCF_Op<"reduce", [
Terminator, HasParent<"ParallelOp">, RecursiveMemoryEffects,
DeclareOpInterfaceMethods<RegionBranchTerminatorOpInterface>]> {
let summary = "reduce operation for scf.parallel";
let description = [{
The `scf.reduce` operation is the terminator for `scf.parallel` operations. It can model
an arbitrary number of reductions. It has one region per reduction. Each
region has one block with two arguments which have the same type as the
corresponding operand of `scf.reduce`. The operands of the op are the values
that should be reduce; one value per reduction.
The i-th reduction (i.e., the i-th region and the i-th operand) corresponds
the i-th initial value and the i-th result of the enclosing `scf.parallel`
op.
The `scf.reduce` operation contains regions whose entry blocks expect two
arguments of the same type as the corresponding operand. As the iteration
order of the enclosing parallel loop and hence reduction order is
unspecified, the results of the reductions may be non-deterministic unless
the reductions are associative and commutative.
The result of a reduction region (`scf.reduce.return` operand) must have the
same type as the corresponding `scf.reduce` operand and the corresponding
`scf.parallel` initial value.
Example:
```mlir
%operand = arith.constant 1.0 : f32
scf.reduce(%operand : f32) {
^bb0(%lhs : f32, %rhs: f32):
%res = arith.addf %lhs, %rhs : f32
scf.reduce.return %res : f32
}
```
}];
let skipDefaultBuilders = 1;
let builders = [
OpBuilder<(ins "ValueRange":$operands)>,
OpBuilder<(ins)>
];
let arguments = (ins Variadic<AnyType>:$operands);
let assemblyFormat = [{
(`(` $operands^ `:` type($operands) `)`)? $reductions attr-dict
}];
let regions = (region VariadicRegion<SizedRegion<1>>:$reductions);
let hasRegionVerifier = 1;
}
//===----------------------------------------------------------------------===//
// ReduceReturnOp
//===----------------------------------------------------------------------===//
def ReduceReturnOp :
SCF_Op<"reduce.return", [HasParent<"ReduceOp">, Pure, Terminator]> {
let summary = "terminator for reduce operation";
let description = [{
The `scf.reduce.return` operation is a special terminator operation for the block inside
`scf.reduce` regions. It terminates the region. It should have the same
operand type as the corresponding operand of the enclosing `scf.reduce` op.
Example:
```mlir
scf.reduce.return %res : f32
```
}];
let arguments = (ins AnyType:$result);
let assemblyFormat = "$result attr-dict `:` type($result)";
let hasVerifier = 1;
}
//===----------------------------------------------------------------------===//
// WhileOp
//===----------------------------------------------------------------------===//
def WhileOp : SCF_Op<"while",
[DeclareOpInterfaceMethods<RegionBranchOpInterface,
["getEntrySuccessorOperands"]>,
DeclareOpInterfaceMethods<LoopLikeOpInterface,
["getRegionIterArgs", "getYieldedValuesMutable"]>,
RecursiveMemoryEffects, SingleBlock]> {
let summary = "a generic 'while' loop";
let description = [{
This operation represents a generic "while"/"do-while" loop that keeps
iterating as long as a condition is satisfied. There is no restriction on
the complexity of the condition. It consists of two regions (with single
block each): "before" region and "after" region. The names of regions
indicates whether they execute before or after the condition check.
Therefore, if the main loop payload is located in the "before" region, the
operation is a "do-while" loop. Otherwise, it is a "while" loop.
The "before" region terminates with a special operation, `scf.condition`,
that accepts as its first operand an `i1` value indicating whether to
proceed to the "after" region (value is `true`) or not. The two regions
communicate by means of region arguments. Initially, the "before" region
accepts as arguments the operands of the `scf.while` operation and uses them
to evaluate the condition. It forwards the trailing, non-condition operands
of the `scf.condition` terminator either to the "after" region if the
control flow is transferred there or to results of the `scf.while` operation
otherwise. The "after" region takes as arguments the values produced by the
"before" region and uses `scf.yield` to supply new arguments for the
"before" region, into which it transfers the control flow unconditionally.
A simple "while" loop can be represented as follows.
```mlir
%res = scf.while (%arg1 = %init1) : (f32) -> f32 {
// "Before" region.
// In a "while" loop, this region computes the condition.
%condition = call @evaluate_condition(%arg1) : (f32) -> i1
// Forward the argument (as result or "after" region argument).
scf.condition(%condition) %arg1 : f32
} do {
^bb0(%arg2: f32):
// "After" region.
// In a "while" loop, this region is the loop body.
%next = call @payload(%arg2) : (f32) -> f32
// Forward the new value to the "before" region.
// The operand types must match the types of the `scf.while` operands.
scf.yield %next : f32
}
```
A simple "do-while" loop can be represented by reducing the "after" block
to a simple forwarder.
```mlir
%res = scf.while (%arg1 = %init1) : (f32) -> f32 {
// "Before" region.
// In a "do-while" loop, this region contains the loop body.
%next = call @payload(%arg1) : (f32) -> f32
// And also evaluates the condition.
%condition = call @evaluate_condition(%arg1) : (f32) -> i1
// Loop through the "after" region.
scf.condition(%condition) %next : f32
} do {
^bb0(%arg2: f32):
// "After" region.
// Forwards the values back to "before" region unmodified.
scf.yield %arg2 : f32
}
```
Note that the types of region arguments need not to match with each other.
The op expects the operand types to match with argument types of the
"before" region; the result types to match with the trailing operand types
of the terminator of the "before" region, and with the argument types of the
"after" region. The following scheme can be used to share the results of
some operations executed in the "before" region with the "after" region,
avoiding the need to recompute them.
```mlir
%res = scf.while (%arg1 = %init1) : (f32) -> i64 {
// One can perform some computations, e.g., necessary to evaluate the
// condition, in the "before" region and forward their results to the
// "after" region.
%shared = call @shared_compute(%arg1) : (f32) -> i64
// Evaluate the condition.
%condition = call @evaluate_condition(%arg1, %shared) : (f32, i64) -> i1
// Forward the result of the shared computation to the "after" region.
// The types must match the arguments of the "after" region as well as
// those of the `scf.while` results.
scf.condition(%condition) %shared : i64
} do {
^bb0(%arg2: i64) {
// Use the partial result to compute the rest of the payload in the
// "after" region.
%res = call @payload(%arg2) : (i64) -> f32
// Forward the new value to the "before" region.
// The operand types must match the types of the `scf.while` operands.
scf.yield %res : f32
}
```
The custom syntax for this operation is as follows.
```
op ::= `scf.while` assignments `:` function-type region `do` region
`attributes` attribute-dict
initializer ::= /* empty */ | `(` assignment-list `)`
assignment-list ::= assignment | assignment `,` assignment-list
assignment ::= ssa-value `=` ssa-value
```
}];
let arguments = (ins Variadic<AnyType>:$inits);
let results = (outs Variadic<AnyType>:$results);
let regions = (region SizedRegion<1>:$before, SizedRegion<1>:$after);
let builders = [
OpBuilder<(ins "TypeRange":$resultTypes, "ValueRange":$inits,
"function_ref<void(OpBuilder &, Location, ValueRange)>":$beforeBuilder,
"function_ref<void(OpBuilder &, Location, ValueRange)>":$afterBuilder)>
];
let extraClassDeclaration = [{
using BodyBuilderFn =
function_ref<void(OpBuilder &, Location, ValueRange)>;
ConditionOp getConditionOp();
YieldOp getYieldOp();
Block::BlockArgListType getBeforeArguments();
Block::BlockArgListType getAfterArguments();
Block *getBeforeBody() { return &getBefore().front(); }
Block *getAfterBody() { return &getAfter().front(); }
}];
let hasCanonicalizer = 1;
let hasCustomAssemblyFormat = 1;
let hasVerifier = 1;
}
//===----------------------------------------------------------------------===//
// IndexSwitchOp
//===----------------------------------------------------------------------===//
def IndexSwitchOp : SCF_Op<"index_switch", [RecursiveMemoryEffects,
SingleBlockImplicitTerminator<"scf::YieldOp">,
DeclareOpInterfaceMethods<RegionBranchOpInterface,
["getRegionInvocationBounds",
"getEntrySuccessorRegions"]>]> {
let summary = "switch-case operation on an index argument";
let description = [{
The `scf.index_switch` is a control-flow operation that branches to one of
the given regions based on the values of the argument and the cases. The
argument is always of type `index`.
The operation always has a "default" region and any number of case regions
denoted by integer constants. Control-flow transfers to the case region
whose constant value equals the value of the argument. If the argument does
not equal any of the case values, control-flow transfer to the "default"
region.
Example:
```mlir
%0 = scf.index_switch %arg0 : index -> i32
case 2 {
%1 = arith.constant 10 : i32
scf.yield %1 : i32
}
case 5 {
%2 = arith.constant 20 : i32
scf.yield %2 : i32
}
default {
%3 = arith.constant 30 : i32
scf.yield %3 : i32
}
```
}];
let arguments = (ins Index:$arg, DenseI64ArrayAttr:$cases);
let results = (outs Variadic<AnyType>:$results);
let regions = (region SizedRegion<1>:$defaultRegion,
VariadicRegion<SizedRegion<1>>:$caseRegions);
let assemblyFormat = [{
$arg attr-dict (`->` type($results)^)?
custom<SwitchCases>($cases, $caseRegions) `\n`
`` `default` $defaultRegion
}];
let extraClassDeclaration = [{
/// Get the number of cases.
unsigned getNumCases();
/// Get the default region body.
Block &getDefaultBlock();
/// Get the body of a case region.
Block &getCaseBlock(unsigned idx);
}];
let hasCanonicalizer = 1;
let hasVerifier = 1;
}
//===----------------------------------------------------------------------===//
// YieldOp
//===----------------------------------------------------------------------===//
def YieldOp : SCF_Op<"yield", [Pure, ReturnLike, Terminator,
ParentOneOf<["ExecuteRegionOp", "ForOp", "IfOp", "IndexSwitchOp",
"WhileOp"]>]> {
let summary = "loop yield and termination operation";
let description = [{
The `scf.yield` operation yields an SSA value from the SCF dialect op region and
terminates the regions. The semantics of how the values are yielded is
defined by the parent operation.
If `scf.yield` has any operands, the operands must match the parent
operation's results.
If the parent operation defines no values, then the `scf.yield` may be
left out in the custom syntax and the builders will insert one implicitly.
Otherwise, it has to be present in the syntax to indicate which values are
yielded.
}];
let arguments = (ins Variadic<AnyType>:$results);
let builders = [OpBuilder<(ins), [{ /* nothing to do */ }]>];
let assemblyFormat =
[{ attr-dict ($results^ `:` type($results))? }];
}
#endif // MLIR_DIALECT_SCF_SCFOPS
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