1 //===- AggressiveInstCombineInternal.h --------------------------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements the instruction pattern combiner classes.
11 // Currently, it handles pattern expressions for:
12 // * Truncate instruction
14 //===----------------------------------------------------------------------===//
16 #include "llvm/ADT/MapVector.h"
17 #include "llvm/ADT/STLExtras.h"
18 #include "llvm/Analysis/AliasAnalysis.h"
19 #include "llvm/Analysis/BasicAliasAnalysis.h"
20 #include "llvm/Analysis/ConstantFolding.h"
21 #include "llvm/Analysis/GlobalsModRef.h"
22 #include "llvm/Analysis/TargetLibraryInfo.h"
23 #include "llvm/IR/DataLayout.h"
24 #include "llvm/Pass.h"
27 //===----------------------------------------------------------------------===//
28 // TruncInstCombine - looks for expression dags dominated by trunc instructions
29 // and for each eligible dag, it will create a reduced bit-width expression and
30 // replace the old expression with this new one and remove the old one.
31 // Eligible expression dag is such that:
32 // 1. Contains only supported instructions.
33 // 2. Supported leaves: ZExtInst, SExtInst, TruncInst and Constant value.
34 // 3. Can be evaluated into type with reduced legal bit-width (or Trunc type).
35 // 4. All instructions in the dag must not have users outside the dag.
36 // Only exception is for {ZExt, SExt}Inst with operand type equal to the
37 // new reduced type chosen in (3).
39 // The motivation for this optimization is that evaluating and expression using
40 // smaller bit-width is preferable, especially for vectorization where we can
41 // fit more values in one vectorized instruction. In addition, this optimization
42 // may decrease the number of cast instructions, but will not increase it.
43 //===----------------------------------------------------------------------===//
48 class TargetLibraryInfo;
50 class TruncInstCombine {
51 TargetLibraryInfo &TLI;
53 const DominatorTree &DT;
55 /// List of all TruncInst instructions to be processed.
56 SmallVector<TruncInst *, 4> Worklist;
58 /// Current processed TruncInst instruction.
59 TruncInst *CurrentTruncInst;
61 /// Information per each instruction in the expression dag.
63 /// Number of LSBs that are needed to generate a valid expression.
64 unsigned ValidBitWidth = 0;
65 /// Minimum number of LSBs needed to generate the ValidBitWidth.
66 unsigned MinBitWidth = 0;
67 /// The reduced value generated to replace the old instruction.
68 Value *NewValue = nullptr;
70 /// An ordered map representing expression dag post-dominated by current
71 /// processed TruncInst. It maps each instruction in the dag to its Info
72 /// structure. The map is ordered such that each instruction appears before
73 /// all other instructions in the dag that uses it.
74 MapVector<Instruction *, Info> InstInfoMap;
77 TruncInstCombine(TargetLibraryInfo &TLI, const DataLayout &DL,
78 const DominatorTree &DT)
79 : TLI(TLI), DL(DL), DT(DT), CurrentTruncInst(nullptr) {}
81 /// Perform TruncInst pattern optimization on given function.
82 bool run(Function &F);
85 /// Build expression dag dominated by the /p CurrentTruncInst and append it to
86 /// the InstInfoMap container.
88 /// \return true only if succeed to generate an eligible sub expression dag.
89 bool buildTruncExpressionDag();
91 /// Calculate the minimal allowed bit-width of the chain ending with the
92 /// currently visited truncate's operand.
94 /// \return minimum number of bits to which the chain ending with the
95 /// truncate's operand can be shrunk to.
96 unsigned getMinBitWidth();
98 /// Build an expression dag dominated by the current processed TruncInst and
99 /// Check if it is eligible to be reduced to a smaller type.
101 /// \return the scalar version of the new type to be used for the reduced
102 /// expression dag, or nullptr if the expression dag is not eligible
104 Type *getBestTruncatedType();
106 /// Given a \p V value and a \p SclTy scalar type return the generated reduced
107 /// value of \p V based on the type \p SclTy.
109 /// \param V value to be reduced.
110 /// \param SclTy scalar version of new type to reduce to.
111 /// \return the new reduced value.
112 Value *getReducedOperand(Value *V, Type *SclTy);
114 /// Create a new expression dag using the reduced /p SclTy type and replace
115 /// the old expression dag with it. Also erase all instructions in the old
116 /// dag, except those that are still needed outside the dag.
118 /// \param SclTy scalar version of new type to reduce expression dag into.
119 void ReduceExpressionDag(Type *SclTy);
121 } // end namespace llvm.