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llvm-mirror/include/llvm/Transforms/Scalar.h
Alexey Zhikhartsev 6516543c4b Add jump-threading optimization for deterministic finite automata
The current JumpThreading pass does not jump thread loops since it can
result in irreducible control flow that harms other optimizations. This
prevents switch statements inside a loop from being optimized to use
unconditional branches.

This code pattern occurs in the core_state_transition function of
Coremark. The state machine can be implemented manually with goto
statements resulting in a large runtime improvement, and this transform
makes the switch implementation match the goto version in performance.

This patch specifically targets switch statements inside a loop that
have the opportunity to be threaded. Once it identifies an opportunity,
it creates new paths that branch directly to the correct code block.
For example, the left CFG could be transformed to the right CFG:

```
          sw.bb                        sw.bb
        /   |   \                    /   |   \
   case1  case2  case3          case1  case2  case3
        \   |   /                /       |       \
        latch.bb             latch.2  latch.3  latch.1
         br sw.bb              /         |         \
                           sw.bb.2     sw.bb.3     sw.bb.1
                            br case2    br case3    br case1
```

Co-author: Justin Kreiner @jkreiner
Co-author: Ehsan Amiri @amehsan

Reviewed By: SjoerdMeijer

Differential Revision: https://reviews.llvm.org/D99205
2021-07-27 14:34:04 -04:00

568 lines
20 KiB
C++

//===-- Scalar.h - Scalar Transformations -----------------------*- C++ -*-===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// This header file defines prototypes for accessor functions that expose passes
// in the Scalar transformations library.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_TRANSFORMS_SCALAR_H
#define LLVM_TRANSFORMS_SCALAR_H
#include "llvm/Transforms/Utils/SimplifyCFGOptions.h"
#include <functional>
namespace llvm {
class Function;
class FunctionPass;
class ModulePass;
class Pass;
//===----------------------------------------------------------------------===//
//
// AlignmentFromAssumptions - Use assume intrinsics to set load/store
// alignments.
//
FunctionPass *createAlignmentFromAssumptionsPass();
//===----------------------------------------------------------------------===//
//
// AnnotationRemarks - Emit remarks for !annotation metadata.
//
FunctionPass *createAnnotationRemarksLegacyPass();
//===----------------------------------------------------------------------===//
//
// SCCP - Sparse conditional constant propagation.
//
FunctionPass *createSCCPPass();
//===----------------------------------------------------------------------===//
//
// RedundantDbgInstElimination - This pass removes redundant dbg intrinsics
// without modifying the CFG of the function. It is a FunctionPass.
//
Pass *createRedundantDbgInstEliminationPass();
//===----------------------------------------------------------------------===//
//
// DeadCodeElimination - This pass is more powerful than DeadInstElimination,
// because it is worklist driven that can potentially revisit instructions when
// their other instructions become dead, to eliminate chains of dead
// computations.
//
FunctionPass *createDeadCodeEliminationPass();
//===----------------------------------------------------------------------===//
//
// DeadStoreElimination - This pass deletes stores that are post-dominated by
// must-aliased stores and are not loaded used between the stores.
//
FunctionPass *createDeadStoreEliminationPass();
//===----------------------------------------------------------------------===//
//
// CallSiteSplitting - This pass split call-site based on its known argument
// values.
FunctionPass *createCallSiteSplittingPass();
//===----------------------------------------------------------------------===//
//
// AggressiveDCE - This pass uses the SSA based Aggressive DCE algorithm. This
// algorithm assumes instructions are dead until proven otherwise, which makes
// it more successful are removing non-obviously dead instructions.
//
FunctionPass *createAggressiveDCEPass();
//===----------------------------------------------------------------------===//
//
// GuardWidening - An optimization over the @llvm.experimental.guard intrinsic
// that (optimistically) combines multiple guards into one to have fewer checks
// at runtime.
//
FunctionPass *createGuardWideningPass();
//===----------------------------------------------------------------------===//
//
// LoopGuardWidening - Analogous to the GuardWidening pass, but restricted to a
// single loop at a time for use within a LoopPassManager. Desired effect is
// to widen guards into preheader or a single guard within loop if that's not
// possible.
//
Pass *createLoopGuardWideningPass();
//===----------------------------------------------------------------------===//
//
// BitTrackingDCE - This pass uses a bit-tracking DCE algorithm in order to
// remove computations of dead bits.
//
FunctionPass *createBitTrackingDCEPass();
//===----------------------------------------------------------------------===//
//
// SROA - Replace aggregates or pieces of aggregates with scalar SSA values.
//
FunctionPass *createSROAPass();
//===----------------------------------------------------------------------===//
//
// InductiveRangeCheckElimination - Transform loops to elide range checks on
// linear functions of the induction variable.
//
Pass *createInductiveRangeCheckEliminationPass();
//===----------------------------------------------------------------------===//
//
// InductionVariableSimplify - Transform induction variables in a program to all
// use a single canonical induction variable per loop.
//
Pass *createIndVarSimplifyPass();
//===----------------------------------------------------------------------===//
//
// LICM - This pass is a loop invariant code motion and memory promotion pass.
//
Pass *createLICMPass();
Pass *createLICMPass(unsigned LicmMssaOptCap,
unsigned LicmMssaNoAccForPromotionCap);
//===----------------------------------------------------------------------===//
//
// LoopSink - This pass sinks invariants from preheader to loop body where
// frequency is lower than loop preheader.
//
Pass *createLoopSinkPass();
//===----------------------------------------------------------------------===//
//
// LoopPredication - This pass does loop predication on guards.
//
Pass *createLoopPredicationPass();
//===----------------------------------------------------------------------===//
//
// LoopInterchange - This pass interchanges loops to provide a more
// cache-friendly memory access patterns.
//
Pass *createLoopInterchangePass();
//===----------------------------------------------------------------------===//
//
// LoopFlatten - This pass flattens nested loops into a single loop.
//
FunctionPass *createLoopFlattenPass();
//===----------------------------------------------------------------------===//
//
// LoopStrengthReduce - This pass is strength reduces GEP instructions that use
// a loop's canonical induction variable as one of their indices.
//
Pass *createLoopStrengthReducePass();
//===----------------------------------------------------------------------===//
//
// LoopUnswitch - This pass is a simple loop unswitching pass.
//
Pass *createLoopUnswitchPass(bool OptimizeForSize = false,
bool hasBranchDivergence = false);
//===----------------------------------------------------------------------===//
//
// LoopInstSimplify - This pass simplifies instructions in a loop's body.
//
Pass *createLoopInstSimplifyPass();
//===----------------------------------------------------------------------===//
//
// LoopUnroll - This pass is a simple loop unrolling pass.
//
Pass *createLoopUnrollPass(int OptLevel = 2, bool OnlyWhenForced = false,
bool ForgetAllSCEV = false, int Threshold = -1,
int Count = -1, int AllowPartial = -1,
int Runtime = -1, int UpperBound = -1,
int AllowPeeling = -1);
// Create an unrolling pass for full unrolling that uses exact trip count only
// and also does peeling.
Pass *createSimpleLoopUnrollPass(int OptLevel = 2, bool OnlyWhenForced = false,
bool ForgetAllSCEV = false);
//===----------------------------------------------------------------------===//
//
// LoopUnrollAndJam - This pass is a simple loop unroll and jam pass.
//
Pass *createLoopUnrollAndJamPass(int OptLevel = 2);
//===----------------------------------------------------------------------===//
//
// LoopReroll - This pass is a simple loop rerolling pass.
//
Pass *createLoopRerollPass();
//===----------------------------------------------------------------------===//
//
// LoopRotate - This pass is a simple loop rotating pass.
//
Pass *createLoopRotatePass(int MaxHeaderSize = -1, bool PrepareForLTO = false);
//===----------------------------------------------------------------------===//
//
// LoopIdiom - This pass recognizes and replaces idioms in loops.
//
Pass *createLoopIdiomPass();
//===----------------------------------------------------------------------===//
//
// LoopVersioningLICM - This pass is a loop versioning pass for LICM.
//
Pass *createLoopVersioningLICMPass();
//===----------------------------------------------------------------------===//
//
// DemoteRegisterToMemoryPass - This pass is used to demote registers to memory
// references. In basically undoes the PromoteMemoryToRegister pass to make cfg
// hacking easier.
//
FunctionPass *createDemoteRegisterToMemoryPass();
extern char &DemoteRegisterToMemoryID;
//===----------------------------------------------------------------------===//
//
// Reassociate - This pass reassociates commutative expressions in an order that
// is designed to promote better constant propagation, GCSE, LICM, PRE...
//
// For example: 4 + (x + 5) -> x + (4 + 5)
//
FunctionPass *createReassociatePass();
//===----------------------------------------------------------------------===//
//
// JumpThreading - Thread control through mult-pred/multi-succ blocks where some
// preds always go to some succ. If FreezeSelectCond is true, unfold the
// condition of a select that unfolds to branch. Thresholds other than minus one
// override the internal BB duplication default threshold.
//
FunctionPass *createJumpThreadingPass(bool FreezeSelectCond = false,
int Threshold = -1);
//===----------------------------------------------------------------------===//
//
// DFAJumpThreading - When a switch statement inside a loop is used to
// implement a deterministic finite automata we can jump thread the switch
// statement reducing number of conditional jumps.
//
FunctionPass *createDFAJumpThreadingPass();
//===----------------------------------------------------------------------===//
//
// CFGSimplification - Merge basic blocks, eliminate unreachable blocks,
// simplify terminator instructions, convert switches to lookup tables, etc.
//
FunctionPass *createCFGSimplificationPass(
SimplifyCFGOptions Options = SimplifyCFGOptions(),
std::function<bool(const Function &)> Ftor = nullptr);
//===----------------------------------------------------------------------===//
//
// FlattenCFG - flatten CFG, reduce number of conditional branches by using
// parallel-and and parallel-or mode, etc...
//
FunctionPass *createFlattenCFGPass();
//===----------------------------------------------------------------------===//
//
// CFG Structurization - Remove irreducible control flow
//
///
/// When \p SkipUniformRegions is true the structizer will not structurize
/// regions that only contain uniform branches.
Pass *createStructurizeCFGPass(bool SkipUniformRegions = false);
//===----------------------------------------------------------------------===//
//
// TailCallElimination - This pass eliminates call instructions to the current
// function which occur immediately before return instructions.
//
FunctionPass *createTailCallEliminationPass();
//===----------------------------------------------------------------------===//
//
// EarlyCSE - This pass performs a simple and fast CSE pass over the dominator
// tree.
//
FunctionPass *createEarlyCSEPass(bool UseMemorySSA = false);
//===----------------------------------------------------------------------===//
//
// GVNHoist - This pass performs a simple and fast GVN pass over the dominator
// tree to hoist common expressions from sibling branches.
//
FunctionPass *createGVNHoistPass();
//===----------------------------------------------------------------------===//
//
// GVNSink - This pass uses an "inverted" value numbering to decide the
// similarity of expressions and sinks similar expressions into successors.
//
FunctionPass *createGVNSinkPass();
//===----------------------------------------------------------------------===//
//
// MergedLoadStoreMotion - This pass merges loads and stores in diamonds. Loads
// are hoisted into the header, while stores sink into the footer.
//
FunctionPass *createMergedLoadStoreMotionPass(bool SplitFooterBB = false);
//===----------------------------------------------------------------------===//
//
// GVN - This pass performs global value numbering and redundant load
// elimination cotemporaneously.
//
FunctionPass *createNewGVNPass();
//===----------------------------------------------------------------------===//
//
// DivRemPairs - Hoist/decompose integer division and remainder instructions.
//
FunctionPass *createDivRemPairsPass();
//===----------------------------------------------------------------------===//
//
// MemCpyOpt - This pass performs optimizations related to eliminating memcpy
// calls and/or combining multiple stores into memset's.
//
FunctionPass *createMemCpyOptPass();
//===----------------------------------------------------------------------===//
//
// LoopDeletion - This pass performs DCE of non-infinite loops that it
// can prove are dead.
//
Pass *createLoopDeletionPass();
//===----------------------------------------------------------------------===//
//
// ConstantHoisting - This pass prepares a function for expensive constants.
//
FunctionPass *createConstantHoistingPass();
//===----------------------------------------------------------------------===//
//
// ConstraintElimination - This pass eliminates conditions based on found
// constraints.
//
FunctionPass *createConstraintEliminationPass();
//===----------------------------------------------------------------------===//
//
// Sink - Code Sinking
//
FunctionPass *createSinkingPass();
//===----------------------------------------------------------------------===//
//
// LowerAtomic - Lower atomic intrinsics to non-atomic form
//
Pass *createLowerAtomicPass();
//===----------------------------------------------------------------------===//
//
// LowerGuardIntrinsic - Lower guard intrinsics to normal control flow.
//
Pass *createLowerGuardIntrinsicPass();
//===----------------------------------------------------------------------===//
//
// LowerMatrixIntrinsics - Lower matrix intrinsics to vector operations.
//
Pass *createLowerMatrixIntrinsicsPass();
//===----------------------------------------------------------------------===//
//
// LowerMatrixIntrinsicsMinimal - Lower matrix intrinsics to vector operations
// (lightweight, does not require extra analysis)
//
Pass *createLowerMatrixIntrinsicsMinimalPass();
//===----------------------------------------------------------------------===//
//
// LowerWidenableCondition - Lower widenable condition to i1 true.
//
Pass *createLowerWidenableConditionPass();
//===----------------------------------------------------------------------===//
//
// MergeICmps - Merge integer comparison chains into a memcmp
//
Pass *createMergeICmpsLegacyPass();
//===----------------------------------------------------------------------===//
//
// ValuePropagation - Propagate CFG-derived value information
//
Pass *createCorrelatedValuePropagationPass();
//===----------------------------------------------------------------------===//
//
// InferAddressSpaces - Modify users of addrspacecast instructions with values
// in the source address space if using the destination address space is slower
// on the target. If AddressSpace is left to its default value, it will be
// obtained from the TargetTransformInfo.
//
FunctionPass *createInferAddressSpacesPass(unsigned AddressSpace = ~0u);
extern char &InferAddressSpacesID;
//===----------------------------------------------------------------------===//
//
// LowerExpectIntrinsics - Removes llvm.expect intrinsics and creates
// "block_weights" metadata.
FunctionPass *createLowerExpectIntrinsicPass();
//===----------------------------------------------------------------------===//
//
// LowerConstantIntrinsicss - Expand any remaining llvm.objectsize and
// llvm.is.constant intrinsic calls, even for the unknown cases.
//
FunctionPass *createLowerConstantIntrinsicsPass();
//===----------------------------------------------------------------------===//
//
// PartiallyInlineLibCalls - Tries to inline the fast path of library
// calls such as sqrt.
//
FunctionPass *createPartiallyInlineLibCallsPass();
//===----------------------------------------------------------------------===//
//
// SeparateConstOffsetFromGEP - Split GEPs for better CSE
//
FunctionPass *createSeparateConstOffsetFromGEPPass(bool LowerGEP = false);
//===----------------------------------------------------------------------===//
//
// SpeculativeExecution - Aggressively hoist instructions to enable
// speculative execution on targets where branches are expensive.
//
FunctionPass *createSpeculativeExecutionPass();
// Same as createSpeculativeExecutionPass, but does nothing unless
// TargetTransformInfo::hasBranchDivergence() is true.
FunctionPass *createSpeculativeExecutionIfHasBranchDivergencePass();
//===----------------------------------------------------------------------===//
//
// StraightLineStrengthReduce - This pass strength-reduces some certain
// instruction patterns in straight-line code.
//
FunctionPass *createStraightLineStrengthReducePass();
//===----------------------------------------------------------------------===//
//
// PlaceSafepoints - Rewrite any IR calls to gc.statepoints and insert any
// safepoint polls (method entry, backedge) that might be required. This pass
// does not generate explicit relocation sequences - that's handled by
// RewriteStatepointsForGC which can be run at an arbitrary point in the pass
// order following this pass.
//
FunctionPass *createPlaceSafepointsPass();
//===----------------------------------------------------------------------===//
//
// RewriteStatepointsForGC - Rewrite any gc.statepoints which do not yet have
// explicit relocations to include explicit relocations.
//
ModulePass *createRewriteStatepointsForGCLegacyPass();
//===----------------------------------------------------------------------===//
//
// Float2Int - Demote floats to ints where possible.
//
FunctionPass *createFloat2IntPass();
//===----------------------------------------------------------------------===//
//
// NaryReassociate - Simplify n-ary operations by reassociation.
//
FunctionPass *createNaryReassociatePass();
//===----------------------------------------------------------------------===//
//
// LoopDistribute - Distribute loops.
//
FunctionPass *createLoopDistributePass();
//===----------------------------------------------------------------------===//
//
// LoopFuse - Fuse loops.
//
FunctionPass *createLoopFusePass();
//===----------------------------------------------------------------------===//
//
// LoopLoadElimination - Perform loop-aware load elimination.
//
FunctionPass *createLoopLoadEliminationPass();
//===----------------------------------------------------------------------===//
//
// LoopVersioning - Perform loop multi-versioning.
//
FunctionPass *createLoopVersioningPass();
//===----------------------------------------------------------------------===//
//
// LoopDataPrefetch - Perform data prefetching in loops.
//
FunctionPass *createLoopDataPrefetchPass();
///===---------------------------------------------------------------------===//
ModulePass *createNameAnonGlobalPass();
ModulePass *createCanonicalizeAliasesPass();
//===----------------------------------------------------------------------===//
//
// LibCallsShrinkWrap - Shrink-wraps a call to function if the result is not
// used.
//
FunctionPass *createLibCallsShrinkWrapPass();
//===----------------------------------------------------------------------===//
//
// LoopSimplifyCFG - This pass performs basic CFG simplification on loops,
// primarily to help other loop passes.
//
Pass *createLoopSimplifyCFGPass();
//===----------------------------------------------------------------------===//
//
// WarnMissedTransformations - This pass emits warnings for leftover forced
// transformations.
//
Pass *createWarnMissedTransformationsPass();
//===----------------------------------------------------------------------===//
//
// This pass does instruction simplification on each
// instruction in a function.
//
FunctionPass *createInstSimplifyLegacyPass();
//===----------------------------------------------------------------------===//
//
// createScalarizeMaskedMemIntrinPass - Replace masked load, store, gather
// and scatter intrinsics with scalar code when target doesn't support them.
//
FunctionPass *createScalarizeMaskedMemIntrinLegacyPass();
} // End llvm namespace
#endif