LLVM 19.0.0git
Delinearization.h
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1//===---- Delinearization.h - MultiDimensional Index Delinearization ------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This implements an analysis pass that tries to delinearize all GEP
10// instructions in all loops using the SCEV analysis functionality. This pass is
11// only used for testing purposes: if your pass needs delinearization, please
12// use the on-demand SCEVAddRecExpr::delinearize() function.
13//
14//===----------------------------------------------------------------------===//
15
16#ifndef LLVM_ANALYSIS_DELINEARIZATION_H
17#define LLVM_ANALYSIS_DELINEARIZATION_H
18
19#include "llvm/IR/PassManager.h"
20
21namespace llvm {
22class raw_ostream;
23template <typename T> class SmallVectorImpl;
24class GetElementPtrInst;
25class ScalarEvolution;
26class SCEV;
27
28/// Compute the array dimensions Sizes from the set of Terms extracted from
29/// the memory access function of this SCEVAddRecExpr (second step of
30/// delinearization).
31void findArrayDimensions(ScalarEvolution &SE,
32 SmallVectorImpl<const SCEV *> &Terms,
33 SmallVectorImpl<const SCEV *> &Sizes,
34 const SCEV *ElementSize);
35
36/// Collect parametric terms occurring in step expressions (first step of
37/// delinearization).
38void collectParametricTerms(ScalarEvolution &SE, const SCEV *Expr,
39 SmallVectorImpl<const SCEV *> &Terms);
40
41/// Return in Subscripts the access functions for each dimension in Sizes
42/// (third step of delinearization).
43void computeAccessFunctions(ScalarEvolution &SE, const SCEV *Expr,
44 SmallVectorImpl<const SCEV *> &Subscripts,
45 SmallVectorImpl<const SCEV *> &Sizes);
46/// Split this SCEVAddRecExpr into two vectors of SCEVs representing the
47/// subscripts and sizes of an array access.
48///
49/// The delinearization is a 3 step process: the first two steps compute the
50/// sizes of each subscript and the third step computes the access functions
51/// for the delinearized array:
52///
53/// 1. Find the terms in the step functions
54/// 2. Compute the array size
55/// 3. Compute the access function: divide the SCEV by the array size
56/// starting with the innermost dimensions found in step 2. The Quotient
57/// is the SCEV to be divided in the next step of the recursion. The
58/// Remainder is the subscript of the innermost dimension. Loop over all
59/// array dimensions computed in step 2.
60///
61/// To compute a uniform array size for several memory accesses to the same
62/// object, one can collect in step 1 all the step terms for all the memory
63/// accesses, and compute in step 2 a unique array shape. This guarantees
64/// that the array shape will be the same across all memory accesses.
65///
66/// FIXME: We could derive the result of steps 1 and 2 from a description of
67/// the array shape given in metadata.
68///
69/// Example:
70///
71/// A[][n][m]
72///
73/// for i
74/// for j
75/// for k
76/// A[j+k][2i][5i] =
77///
78/// The initial SCEV:
79///
80/// A[{{{0,+,2*m+5}_i, +, n*m}_j, +, n*m}_k]
81///
82/// 1. Find the different terms in the step functions:
83/// -> [2*m, 5, n*m, n*m]
84///
85/// 2. Compute the array size: sort and unique them
86/// -> [n*m, 2*m, 5]
87/// find the GCD of all the terms = 1
88/// divide by the GCD and erase constant terms
89/// -> [n*m, 2*m]
90/// GCD = m
91/// divide by GCD -> [n, 2]
92/// remove constant terms
93/// -> [n]
94/// size of the array is A[unknown][n][m]
95///
96/// 3. Compute the access function
97/// a. Divide {{{0,+,2*m+5}_i, +, n*m}_j, +, n*m}_k by the innermost size m
98/// Quotient: {{{0,+,2}_i, +, n}_j, +, n}_k
99/// Remainder: {{{0,+,5}_i, +, 0}_j, +, 0}_k
100/// The remainder is the subscript of the innermost array dimension: [5i].
101///
102/// b. Divide Quotient: {{{0,+,2}_i, +, n}_j, +, n}_k by next outer size n
103/// Quotient: {{{0,+,0}_i, +, 1}_j, +, 1}_k
104/// Remainder: {{{0,+,2}_i, +, 0}_j, +, 0}_k
105/// The Remainder is the subscript of the next array dimension: [2i].
106///
107/// The subscript of the outermost dimension is the Quotient: [j+k].
108///
109/// Overall, we have: A[][n][m], and the access function: A[j+k][2i][5i].
110void delinearize(ScalarEvolution &SE, const SCEV *Expr,
111 SmallVectorImpl<const SCEV *> &Subscripts,
112 SmallVectorImpl<const SCEV *> &Sizes, const SCEV *ElementSize);
113
114/// Gathers the individual index expressions from a GEP instruction.
115///
116/// This function optimistically assumes the GEP references into a fixed size
117/// array. If this is actually true, this function returns a list of array
118/// subscript expressions in \p Subscripts and a list of integers describing
119/// the size of the individual array dimensions in \p Sizes. Both lists have
120/// either equal length or the size list is one element shorter in case there
121/// is no known size available for the outermost array dimension. Returns true
122/// if successful and false otherwise.
123bool getIndexExpressionsFromGEP(ScalarEvolution &SE,
124 const GetElementPtrInst *GEP,
125 SmallVectorImpl<const SCEV *> &Subscripts,
126 SmallVectorImpl<int> &Sizes);
127
128/// Implementation of fixed size array delinearization. Try to delinearize
129/// access function for a fixed size multi-dimensional array, by deriving
130/// subscripts from GEP instructions. Returns true upon success and false
131/// otherwise. \p Inst is the load/store instruction whose pointer operand is
132/// the one we want to delinearize. \p AccessFn is its corresponding SCEV
133/// expression w.r.t. the surrounding loop.
134bool tryDelinearizeFixedSizeImpl(ScalarEvolution *SE, Instruction *Inst,
135 const SCEV *AccessFn,
136 SmallVectorImpl<const SCEV *> &Subscripts,
137 SmallVectorImpl<int> &Sizes);
138
140 : public PassInfoMixin<DelinearizationPrinterPass> {
143 static bool isRequired() { return true; }
144
145private:
147};
148} // namespace llvm
149
150#endif // LLVM_ANALYSIS_DELINEARIZATION_H
Hexagon Common GEP
#define F(x, y, z)
Definition: MD5.cpp:55
This header defines various interfaces for pass management in LLVM.
raw_pwrite_stream & OS
A container for analyses that lazily runs them and caches their results.
Definition: PassManager.h:348
A set of analyses that are preserved following a run of a transformation pass.
Definition: Analysis.h:109
This class implements an extremely fast bulk output stream that can only output to a stream.
Definition: raw_ostream.h:52
This is an optimization pass for GlobalISel generic memory operations.
Definition: AddressRanges.h:18
void collectParametricTerms(ScalarEvolution &SE, const SCEV *Expr, SmallVectorImpl< const SCEV * > &Terms)
Collect parametric terms occurring in step expressions (first step of delinearization).
void findArrayDimensions(ScalarEvolution &SE, SmallVectorImpl< const SCEV * > &Terms, SmallVectorImpl< const SCEV * > &Sizes, const SCEV *ElementSize)
Compute the array dimensions Sizes from the set of Terms extracted from the memory access function of...
void computeAccessFunctions(ScalarEvolution &SE, const SCEV *Expr, SmallVectorImpl< const SCEV * > &Subscripts, SmallVectorImpl< const SCEV * > &Sizes)
Return in Subscripts the access functions for each dimension in Sizes (third step of delinearization)...
bool getIndexExpressionsFromGEP(ScalarEvolution &SE, const GetElementPtrInst *GEP, SmallVectorImpl< const SCEV * > &Subscripts, SmallVectorImpl< int > &Sizes)
Gathers the individual index expressions from a GEP instruction.
bool tryDelinearizeFixedSizeImpl(ScalarEvolution *SE, Instruction *Inst, const SCEV *AccessFn, SmallVectorImpl< const SCEV * > &Subscripts, SmallVectorImpl< int > &Sizes)
Implementation of fixed size array delinearization.
void delinearize(ScalarEvolution &SE, const SCEV *Expr, SmallVectorImpl< const SCEV * > &Subscripts, SmallVectorImpl< const SCEV * > &Sizes, const SCEV *ElementSize)
Split this SCEVAddRecExpr into two vectors of SCEVs representing the subscripts and sizes of an array...
PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM)
A CRTP mix-in to automatically provide informational APIs needed for passes.
Definition: PassManager.h:91