MLIR  19.0.0git
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EliminateBarriers.cpp File Reference
#include "mlir/Dialect/Func/IR/FuncOps.h"
#include "mlir/Dialect/GPU/IR/GPUDialect.h"
#include "mlir/Dialect/GPU/Transforms/Passes.h"
#include "mlir/Dialect/MemRef/IR/MemRef.h"
#include "mlir/Dialect/SCF/IR/SCF.h"
#include "mlir/Dialect/Vector/IR/VectorOps.h"
#include "mlir/IR/Operation.h"
#include "mlir/Pass/Pass.h"
#include "mlir/Transforms/GreedyPatternRewriteDriver.h"
#include "llvm/ADT/TypeSwitch.h"
#include "llvm/Support/Debug.h"
#include "mlir/Dialect/GPU/Transforms/Passes.h.inc"

Go to the source code of this file.

Namespaces

 mlir
 Include the generated interface declarations.
 

Macros

#define GEN_PASS_DEF_GPUELIMINATEBARRIERS
 
#define DEBUG_TYPE   "gpu-erase-barriers"
 
#define DEBUG_TYPE_ALIAS   "gpu-erase-barries-alias"
 
#define DBGS()   (llvm::dbgs() << '[' << DEBUG_TYPE << "] ")
 
#define DBGS_ALIAS()   (llvm::dbgs() << '[' << DEBUG_TYPE_ALIAS << "] ")
 

Functions

static bool isKnownNoEffectsOpWithoutInterface (Operation *op)
 Implement the MemoryEffectsOpInterface in the suitable way. More...
 
static bool isParallelRegionBoundary (Operation *op)
 Returns true if the op is defines the parallel region that is subject to barrier synchronization. More...
 
static bool isSequentialLoopLike (Operation *op)
 Returns true if the op behaves like a sequential loop, e.g., the control flow "wraps around" from the end of the body region back to its start. More...
 
static bool hasSingleExecutionBody (Operation *op)
 Returns true if the regions of the op are guaranteed to be executed at most once. More...
 
static bool producesDistinctBase (Operation *op)
 Returns true if the operation is known to produce a pointer-like object distinct from any other object produced by a similar operation. More...
 
static void addAllValuelessEffects (SmallVectorImpl< MemoryEffects::EffectInstance > &effects)
 Populates effects with all memory effects without associating them to a specific value. More...
 
static bool collectEffects (Operation *op, SmallVectorImpl< MemoryEffects::EffectInstance > &effects, bool ignoreBarriers=true)
 Collect the memory effects of the given op in 'effects'. More...
 
static bool getEffectsBefore (Operation *op, SmallVectorImpl< MemoryEffects::EffectInstance > &effects, bool stopAtBarrier)
 Collects memory effects from operations that may be executed before op in a trivial structured control flow, e.g., without branches. More...
 
static bool getEffectsAfter (Operation *op, SmallVectorImpl< MemoryEffects::EffectInstance > &effects, bool stopAtBarrier)
 Collects memory effects from operations that may be executed after op in a trivial structured control flow, e.g., without branches. More...
 
static Value getBase (Value v)
 Looks through known "view-like" ops to find the base memref. More...
 
static bool isFunctionArgument (Value v)
 Returns true if the value is defined as a function argument. More...
 
static Value propagatesCapture (Operation *op)
 Returns the operand that the operation "propagates" through it for capture purposes. More...
 
static std::optional< bool > getKnownCapturingStatus (Operation *op, Value v)
 Returns true if the given operation is known to capture the given value, false if it is known not to capture the given value, nullopt if neither is known. More...
 
static bool maybeCaptured (Value v)
 Returns true if the value may be captured by any of its users, i.e., if the user may be storing this value into memory. More...
 
static bool mayAlias (Value first, Value second)
 Returns true if two values may be referencing aliasing memory. More...
 
static bool mayAlias (MemoryEffects::EffectInstance a, Value v2)
 Returns true if the effect may be affecting memory aliasing the value. More...
 
static bool mayAlias (MemoryEffects::EffectInstance a, MemoryEffects::EffectInstance b)
 Returns true if the two effects may be affecting aliasing memory. More...
 
static bool haveConflictingEffects (ArrayRef< MemoryEffects::EffectInstance > beforeEffects, ArrayRef< MemoryEffects::EffectInstance > afterEffects)
 Returns true if any of the "before" effect instances has a conflict with any "after" instance for the purpose of barrier elimination. More...
 

Macro Definition Documentation

◆ DBGS

#define DBGS ( )    (llvm::dbgs() << '[' << DEBUG_TYPE << "] ")

Definition at line 41 of file EliminateBarriers.cpp.

◆ DBGS_ALIAS

#define DBGS_ALIAS ( )    (llvm::dbgs() << '[' << DEBUG_TYPE_ALIAS << "] ")

Definition at line 42 of file EliminateBarriers.cpp.

◆ DEBUG_TYPE

#define DEBUG_TYPE   "gpu-erase-barriers"

Definition at line 38 of file EliminateBarriers.cpp.

◆ DEBUG_TYPE_ALIAS

#define DEBUG_TYPE_ALIAS   "gpu-erase-barries-alias"

Definition at line 39 of file EliminateBarriers.cpp.

◆ GEN_PASS_DEF_GPUELIMINATEBARRIERS

#define GEN_PASS_DEF_GPUELIMINATEBARRIERS

Definition at line 31 of file EliminateBarriers.cpp.

Function Documentation

◆ addAllValuelessEffects()

static void addAllValuelessEffects ( SmallVectorImpl< MemoryEffects::EffectInstance > &  effects)
static

Populates effects with all memory effects without associating them to a specific value.

Definition at line 83 of file EliminateBarriers.cpp.

◆ collectEffects()

static bool collectEffects ( Operation op,
SmallVectorImpl< MemoryEffects::EffectInstance > &  effects,
bool  ignoreBarriers = true 
)
static

Collect the memory effects of the given op in 'effects'.

Returns 'true' if it could extract the effect information from the op, otherwise returns 'false' and conservatively populates the list with all possible effects associated with no particular value or symbol.

Definition at line 96 of file EliminateBarriers.cpp.

◆ getBase()

static Value getBase ( Value  v)
static

◆ getEffectsAfter()

static bool getEffectsAfter ( Operation op,
SmallVectorImpl< MemoryEffects::EffectInstance > &  effects,
bool  stopAtBarrier 
)
static

Collects memory effects from operations that may be executed after op in a trivial structured control flow, e.g., without branches.

Stops at the parallel region boundary or at the barrier operation if stopAtBarrier is set. Returns true if the memory effects added to effects are exact, false if they are a conservative over-approximation. The latter means that effects contain instances not associated with a specific value.

Definition at line 222 of file EliminateBarriers.cpp.

◆ getEffectsBefore()

static bool getEffectsBefore ( Operation op,
SmallVectorImpl< MemoryEffects::EffectInstance > &  effects,
bool  stopAtBarrier 
)
static

Collects memory effects from operations that may be executed before op in a trivial structured control flow, e.g., without branches.

Stops at the parallel region boundary or at the barrier operation if stopAtBarrier is set. Returns true if the memory effects added to effects are exact, false if they are a conservative over-approximation. The latter means that effects contain instances not associated with a specific value.

Definition at line 142 of file EliminateBarriers.cpp.

◆ getKnownCapturingStatus()

static std::optional<bool> getKnownCapturingStatus ( Operation op,
Value  v 
)
static

Returns true if the given operation is known to capture the given value, false if it is known not to capture the given value, nullopt if neither is known.

Definition at line 349 of file EliminateBarriers.cpp.

Referenced by maybeCaptured().

◆ hasSingleExecutionBody()

static bool hasSingleExecutionBody ( Operation op)
static

Returns true if the regions of the op are guaranteed to be executed at most once.

Thus, if an operation in one of the nested regions of op is executed than so are all the other operations in this region.

Definition at line 70 of file EliminateBarriers.cpp.

◆ haveConflictingEffects()

static bool haveConflictingEffects ( ArrayRef< MemoryEffects::EffectInstance beforeEffects,
ArrayRef< MemoryEffects::EffectInstance afterEffects 
)
static

Returns true if any of the "before" effect instances has a conflict with any "after" instance for the purpose of barrier elimination.

The effects are supposed to be limited to a barrier synchronization scope. A conflict exists if effects instances affect aliasing memory locations and at least on of then as a write. As an exception, if the non-write effect is an allocation effect, there is no conflict since we are only expected to see the allocation happening in the same thread and it cannot be accessed from another thread without capture (which we do handle in alias analysis).

Definition at line 519 of file EliminateBarriers.cpp.

References DBGS, and mayAlias().

◆ isFunctionArgument()

static bool isFunctionArgument ( Value  v)
static

Returns true if the value is defined as a function argument.

Definition at line 327 of file EliminateBarriers.cpp.

Referenced by mayAlias().

◆ isKnownNoEffectsOpWithoutInterface()

static bool isKnownNoEffectsOpWithoutInterface ( Operation op)
static

Implement the MemoryEffectsOpInterface in the suitable way.

Definition at line 48 of file EliminateBarriers.cpp.

◆ isParallelRegionBoundary()

static bool isParallelRegionBoundary ( Operation op)
static

Returns true if the op is defines the parallel region that is subject to barrier synchronization.

Definition at line 56 of file EliminateBarriers.cpp.

◆ isSequentialLoopLike()

static bool isSequentialLoopLike ( Operation op)
static

Returns true if the op behaves like a sequential loop, e.g., the control flow "wraps around" from the end of the body region back to its start.

Definition at line 65 of file EliminateBarriers.cpp.

◆ mayAlias() [1/3]

static bool mayAlias ( MemoryEffects::EffectInstance  a,
MemoryEffects::EffectInstance  b 
)
static

Returns true if the two effects may be affecting aliasing memory.

If an effect is not associated with any value, it is assumed to affect all memory and therefore aliases with everything. Effects on different resources cannot alias.

Definition at line 498 of file EliminateBarriers.cpp.

References mlir::SideEffects::EffectInstance< EffectT >::getResource(), mlir::SideEffects::Resource::getResourceID(), mlir::SideEffects::EffectInstance< EffectT >::getValue(), and mayAlias().

◆ mayAlias() [2/3]

static bool mayAlias ( MemoryEffects::EffectInstance  a,
Value  v2 
)
static

Returns true if the effect may be affecting memory aliasing the value.

If the effect is not associated with any value, it is assumed to affect all memory and therefore aliases with everything.

Definition at line 487 of file EliminateBarriers.cpp.

References mlir::SideEffects::EffectInstance< EffectT >::getValue(), and mayAlias().

◆ mayAlias() [3/3]

static bool mayAlias ( Value  first,
Value  second 
)
static

Returns true if two values may be referencing aliasing memory.

This is a rather naive and conservative analysis. Values defined by different allocation-like operations as well as values derived from those by casts and views cannot alias each other. Similarly, values defined by allocations inside a function cannot alias function arguments. Global values cannot alias each other or local allocations. Values that are captured, i.e. themselves potentially stored in memory, are considered as aliasing with everything. This seems sufficient to achieve barrier removal in structured control flow, more complex cases would require a proper dataflow analysis.

Definition at line 410 of file EliminateBarriers.cpp.

References DBGS_ALIAS, DEBUG_TYPE_ALIAS, getBase(), mlir::Value::getDefiningOp(), isFunctionArgument(), maybeCaptured(), and producesDistinctBase().

Referenced by mlir::affine::affineScalarReplace(), findUnusedStore(), forwardStoreToLoad(), fuseIfLegal(), haveConflictingEffects(), haveNoReadsAfterWriteExceptSameIndex(), isFusionLegal(), loadCSE(), mayAlias(), and verifyDependencies().

◆ maybeCaptured()

static bool maybeCaptured ( Value  v)
static

Returns true if the value may be captured by any of its users, i.e., if the user may be storing this value into memory.

This makes aliasing analysis more conservative as it cannot assume the pointer-like value is only passed around through SSA use-def.

Definition at line 367 of file EliminateBarriers.cpp.

References mlir::SideEffects::EffectInstance< EffectT >::getEffect(), getKnownCapturingStatus(), mlir::Value::getUsers(), and propagatesCapture().

Referenced by mayAlias().

◆ producesDistinctBase()

static bool producesDistinctBase ( Operation op)
static

Returns true if the operation is known to produce a pointer-like object distinct from any other object produced by a similar operation.

For example, an allocation produces such an object.

Definition at line 77 of file EliminateBarriers.cpp.

Referenced by mayAlias().

◆ propagatesCapture()

static Value propagatesCapture ( Operation op)
static

Returns the operand that the operation "propagates" through it for capture purposes.

That is, if the value produced by this operation is captured, then so is the returned value.

Definition at line 335 of file EliminateBarriers.cpp.

Referenced by maybeCaptured().