LLVM  6.0.0svn
Reassociate.cpp File Reference
#include "llvm/Transforms/Scalar/Reassociate.h"
#include "llvm/ADT/APFloat.h"
#include "llvm/ADT/APInt.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/PostOrderIterator.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/GlobalsModRef.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/Argument.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/Constant.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Operator.h"
#include "llvm/IR/PassManager.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/User.h"
#include "llvm/IR/Value.h"
#include "llvm/IR/ValueHandle.h"
#include "llvm/Pass.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/Local.h"
#include <algorithm>
#include <cassert>
#include <utility>
Include dependency graph for Reassociate.cpp:

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## Classes

class  llvm::reassociate::XorOpnd
Utility class representing a non-constant Xor-operand. More...

## Macros

#define DEBUG_TYPE   "reassociate"

## Typedefs

using RepeatedValue = std::pair< Value *, APInt >

## Functions

STATISTIC (NumChanged, "Number of insts reassociated")

STATISTIC (NumAnnihil, "Number of expr tree annihilated")

STATISTIC (NumFactor, "Number of multiplies factored")

static void PrintOps (Instruction *I, const SmallVectorImpl< ValueEntry > &Ops)
Print out the expression identified in the Ops list. More...

static BinaryOperatorisReassociableOp (Value *V, unsigned Opcode)
Return true if V is an instruction of the specified opcode and if it only has one use. More...

static BinaryOperatorisReassociableOp (Value *V, unsigned Opcode1, unsigned Opcode2)

static BinaryOperatorCreateAdd (Value *S1, Value *S2, const Twine &Name, Instruction *InsertBefore, Value *FlagsOp)

static BinaryOperatorCreateMul (Value *S1, Value *S2, const Twine &Name, Instruction *InsertBefore, Value *FlagsOp)

static BinaryOperatorCreateNeg (Value *S1, const Twine &Name, Instruction *InsertBefore, Value *FlagsOp)

static BinaryOperatorLowerNegateToMultiply (Instruction *Neg)
Replace 0-X with X*-1. More...

static unsigned CarmichaelShift (unsigned Bitwidth)
Returns k such that lambda(2^Bitwidth) = 2^k, where lambda is the Carmichael function. More...

static void IncorporateWeight (APInt &LHS, const APInt &RHS, unsigned Opcode)
Add the extra weight 'RHS' to the existing weight 'LHS', reducing the combined weight using any special properties of the operation. More...

static bool LinearizeExprTree (BinaryOperator *I, SmallVectorImpl< RepeatedValue > &Ops)
Given an associative binary expression, return the leaf nodes in Ops along with their weights (how many times the leaf occurs). More...

static ValueNegateValue (Value *V, Instruction *BI, SetVector< AssertingVH< Instruction >> &ToRedo)
Insert instructions before the instruction pointed to by BI, that computes the negative version of the value specified. More...

static bool ShouldBreakUpSubtract (Instruction *Sub)
Return true if we should break up this subtract of X-Y into (X + -Y). More...

static BinaryOperatorBreakUpSubtract (Instruction *Sub, SetVector< AssertingVH< Instruction >> &ToRedo)
If we have (X-Y), and if either X is an add, or if this is only used by an add, transform this into (X+(0-Y)) to promote better reassociation. More...

static BinaryOperatorConvertShiftToMul (Instruction *Shl)
If this is a shift of a reassociable multiply or is used by one, change this into a multiply by a constant to assist with further reassociation. More...

static unsigned FindInOperandList (const SmallVectorImpl< ValueEntry > &Ops, unsigned i, Value *X)
Scan backwards and forwards among values with the same rank as element i to see if X exists. More...

static ValueEmitAddTreeOfValues (Instruction *I, SmallVectorImpl< WeakTrackingVH > &Ops)
Emit a tree of add instructions, summing Ops together and returning the result. More...

static void FindSingleUseMultiplyFactors (Value *V, SmallVectorImpl< Value *> &Factors)
If V is a single-use multiply, recursively add its operands as factors, otherwise add V to the list of factors. More...

static ValueOptimizeAndOrXor (unsigned Opcode, SmallVectorImpl< ValueEntry > &Ops)
Optimize a series of operands to an 'and', 'or', or 'xor' instruction. More...

static ValuecreateAndInstr (Instruction *InsertBefore, Value *Opnd, const APInt &ConstOpnd)
Helper function of CombineXorOpnd(). More...

static bool collectMultiplyFactors (SmallVectorImpl< ValueEntry > &Ops, SmallVectorImpl< Factor > &Factors)
Build up a vector of value/power pairs factoring a product. More...

static ValuebuildMultiplyTree (IRBuilder<> &Builder, SmallVectorImpl< Value *> &Ops)
Build a tree of multiplies, computing the product of Ops. More...

INITIALIZE_PASS (ReassociateLegacyPass, "reassociate", "Reassociate expressions", false, false) FunctionPass *llvm

## ◆ DEBUG_TYPE

 #define DEBUG_TYPE   "reassociate"

Definition at line 65 of file Reassociate.cpp.

## ◆ RepeatedValue

 using RepeatedValue = std::pair

Definition at line 370 of file Reassociate.cpp.

## ◆ BreakUpSubtract()

 static BinaryOperator* BreakUpSubtract ( Instruction * Sub, SetVector< AssertingVH< Instruction >> & ToRedo )
static

If we have (X-Y), and if either X is an add, or if this is only used by an add, transform this into (X+(0-Y)) to promote better reassociation.

Definition at line 915 of file Reassociate.cpp.

Referenced by buildMultiplyTree().

## ◆ CarmichaelShift()

 static unsigned CarmichaelShift ( unsigned Bitwidth )
static

Returns k such that lambda(2^Bitwidth) = 2^k, where lambda is the Carmichael function.

This means that x^(2^k) === 1 mod 2^Bitwidth for every odd x, i.e. x^(2^k) = 1 for every odd x in Bitwidth-bit arithmetic. Note that 0 <= k < Bitwidth, and if Bitwidth > 3 then x^(2^k) = 0 for every even x in Bitwidth-bit arithmetic.

Definition at line 284 of file Reassociate.cpp.

Referenced by IncorporateWeight().

## ◆ collectMultiplyFactors()

 static bool collectMultiplyFactors ( SmallVectorImpl< ValueEntry > & Ops, SmallVectorImpl< Factor > & Factors )
static

Build up a vector of value/power pairs factoring a product.

Given a series of multiplication operands, build a vector of factors and the powers each is raised to when forming the final product. Sort them in the order of descending power.

 (x*x)          -> [(x, 2)]
((x*x)*x)       -> [(x, 3)]


((((x*y)*x)*y)*x) -> [(x, 3), (y, 2)]

Returns
Whether any factors have a power greater than one.

Definition at line 1635 of file Reassociate.cpp.

Referenced by buildMultiplyTree().

## ◆ ConvertShiftToMul()

 static BinaryOperator* ConvertShiftToMul ( Instruction * Shl )
static

If this is a shift of a reassociable multiply or is used by one, change this into a multiply by a constant to assist with further reassociation.

Definition at line 937 of file Reassociate.cpp.

Referenced by buildMultiplyTree().

 static BinaryOperator* CreateAdd ( Value * S1, Value * S2, const Twine & Name, Instruction * InsertBefore, Value * FlagsOp )
static

## ◆ createAndInstr()

 static Value* createAndInstr ( Instruction * InsertBefore, Value * Opnd, const APInt & ConstOpnd )
static

Helper function of CombineXorOpnd().

It creates a bitwise-and instruction with the given two operands, and return the resulting instruction. There are two special cases: 1) if the constant operand is 0, it will return NULL. 2) if the constant is ~0, the symbolic operand will be returned.

Definition at line 1143 of file Reassociate.cpp.

## ◆ CreateMul()

 static BinaryOperator* CreateMul ( Value * S1, Value * S2, const Twine & Name, Instruction * InsertBefore, Value * FlagsOp )
static

## ◆ CreateNeg()

 static BinaryOperator* CreateNeg ( Value * S1, const Twine & Name, Instruction * InsertBefore, Value * FlagsOp )
static

Definition at line 254 of file Reassociate.cpp.

 static Value* EmitAddTreeOfValues ( Instruction * I, SmallVectorImpl< WeakTrackingVH > & Ops )
static

Emit a tree of add instructions, summing Ops together and returning the result.

Insert the tree before I.

Definition at line 990 of file Reassociate.cpp.

Referenced by createAndInstr().

## ◆ FindInOperandList()

 static unsigned FindInOperandList ( const SmallVectorImpl< ValueEntry > & Ops, unsigned i, Value * X )
static

Scan backwards and forwards among values with the same rank as element i to see if X exists.

If X does not exist, return i. This is useful when scanning for 'x' when we see '-x' because they both get the same rank.

Definition at line 964 of file Reassociate.cpp.

References llvm::SmallVectorTemplateCommon< T >::size().

Referenced by createAndInstr(), and OptimizeAndOrXor().

## ◆ FindSingleUseMultiplyFactors()

 static void FindSingleUseMultiplyFactors ( Value * V, SmallVectorImpl< Value *> & Factors )
static

If V is a single-use multiply, recursively add its operands as factors, otherwise add V to the list of factors.

Ops is the top-level list of add operands we're trying to factor.

Definition at line 1077 of file Reassociate.cpp.

Referenced by createAndInstr().

## ◆ IncorporateWeight()

 static void IncorporateWeight ( APInt & LHS, const APInt & RHS, unsigned Opcode )
static

Add the extra weight 'RHS' to the existing weight 'LHS', reducing the combined weight using any special properties of the operation.

The existing weight LHS represents the computation X op X op ... op X where X occurs LHS times. The combined weight represents X op X op ... op X with X occurring LHS + RHS times. If op is "Xor" for example then the combined operation is equivalent to X if LHS + RHS is odd, or 0 if LHS + RHS is even; the routine returns 1 in LHS in the first case, and 0 in LHS in the second.

CM - The value of Carmichael's lambda function.

Definition at line 297 of file Reassociate.cpp.

Referenced by LinearizeExprTree().

## ◆ INITIALIZE_PASS()

 INITIALIZE_PASS ( ReassociateLegacyPass , "reassociate" , "Reassociate expressions" , false , false )

Definition at line 2287 of file Reassociate.cpp.

## ◆ isReassociableOp() [1/2]

 static BinaryOperator* isReassociableOp ( Value * V, unsigned Opcode )
static

Return true if V is an instruction of the specified opcode and if it only has one use.

Definition at line 145 of file Reassociate.cpp.

References llvm::dyn_cast(), and I.

## ◆ isReassociableOp() [2/2]

 static BinaryOperator* isReassociableOp ( Value * V, unsigned Opcode1, unsigned Opcode2 )
static

Definition at line 153 of file Reassociate.cpp.

## ◆ LinearizeExprTree()

 static bool LinearizeExprTree ( BinaryOperator * I, SmallVectorImpl< RepeatedValue > & Ops )
static

Given an associative binary expression, return the leaf nodes in Ops along with their weights (how many times the leaf occurs).

The original expression is the same as (Ops[0].first op Ops[0].first op ... Ops[0].first) <- Ops[0].second times op (Ops[1].first op Ops[1].first op ... Ops[1].first) <- Ops[1].second times op ... op (Ops[N].first op Ops[N].first op ... Ops[N].first) <- Ops[N].second times

Note that the values Ops[0].first, ..., Ops[N].first are all distinct.

This routine may modify the function, in which case it returns 'true'. The changes it makes may well be destructive, changing the value computed by 'I' to something completely different. Thus if the routine returns 'true' then you MUST either replace I with a new expression computed from the Ops array, or use RewriteExprTree to put the values back in.

A leaf node is either not a binary operation of the same kind as the root node 'I' (i.e. is not a binary operator at all, or is, but with a different opcode), or is the same kind of binary operator but has a use which either does not belong to the expression, or does belong to the expression but is a leaf node. Every leaf node has at least one use that is a non-leaf node of the expression, while for non-leaf nodes (except for the root 'I') every use is a non-leaf node of the expression.

For example: expression graph node names

      +        |        I
/ \       |
+   +      |      A,  B
/ \ / \     |
*   +   *    |    C,  D,  E
/ \ / \ / \   |
+   *      |      F,  G


The leaf nodes are C, E, F and G. The Ops array will contain (maybe not in that order) (C, 1), (E, 1), (F, 2), (G, 2).

The expression is maximal: if some instruction is a binary operator of the same kind as 'I', and all of its uses are non-leaf nodes of the expression, then the instruction also belongs to the expression, is not a leaf node of it, and its operands also belong to the expression (but may be leaf nodes).

NOTE: This routine will set operands of non-leaf non-root nodes to undef in order to ensure that every non-root node in the expression has exactly one use by a non-leaf node of the expression. This destruction means that the caller MUST either replace 'I' with a new expression or use something like RewriteExprTree to put the values back in if the routine indicates that it made a change by returning 'true'.

In the above example either the right operand of A or the left operand of B will be replaced by undef. If it is B's operand then this gives:

                +        |        I
/ \       |
+   +      |      A,  B - operand of B replaced with undef
/ \   \     |
*   +   *    |    C,  D,  E
/ \ / \ / \   |
+   *      |      F,  G


Note that such undef operands can only be reached by passing through 'I'. For example, if you visit operands recursively starting from a leaf node then you will never see such an undef operand unless you get back to 'I', which requires passing through a phi node.

Note that this routine may also mutate binary operators of the wrong type that have all uses inside the expression (i.e. only used by non-leaf nodes of the expression) if it can turn them into binary operators of the right type and thus make the expression bigger.

Definition at line 445 of file Reassociate.cpp.

## ◆ LowerNegateToMultiply()

 static BinaryOperator* LowerNegateToMultiply ( Instruction * Neg )
static

Replace 0-X with X*-1.

Definition at line 266 of file Reassociate.cpp.

Referenced by buildMultiplyTree(), and LinearizeExprTree().

## ◆ NegateValue()

 static Value* NegateValue ( Value * V, Instruction * BI, SetVector< AssertingVH< Instruction >> & ToRedo )
static

Insert instructions before the instruction pointed to by BI, that computes the negative version of the value specified.

The negative version of the value is returned, and BI is left pointing at the instruction that should be processed next by the reassociation pass. Also add intermediate instructions to the redo list that are modified while pushing the negates through adds. These will be revisited to see if additional opportunities have been exposed.

Definition at line 799 of file Reassociate.cpp.

Referenced by BreakUpSubtract().

## ◆ OptimizeAndOrXor()

 static Value* OptimizeAndOrXor ( unsigned Opcode, SmallVectorImpl< ValueEntry > & Ops )
static

Optimize a series of operands to an 'and', 'or', or 'xor' instruction.

This optimizes based on identities. If it can be reduced to a single Value, it is returned, otherwise the Ops list is mutated as necessary.

Definition at line 1093 of file Reassociate.cpp.

Referenced by buildMultiplyTree(), and createAndInstr().

## ◆ PrintOps()

 static void PrintOps ( Instruction * I, const SmallVectorImpl< ValueEntry > & Ops )
static

Print out the expression identified in the Ops list.

Definition at line 73 of file Reassociate.cpp.

Referenced by buildMultiplyTree().

## ◆ ShouldBreakUpSubtract()

 static bool ShouldBreakUpSubtract ( Instruction * Sub )
static

Return true if we should break up this subtract of X-Y into (X + -Y).

Definition at line 884 of file Reassociate.cpp.

Referenced by buildMultiplyTree().

## ◆ STATISTIC() [1/3]

 STATISTIC ( NumChanged , "Number of insts reassociated" )

## ◆ STATISTIC() [2/3]

 STATISTIC ( NumAnnihil , "Number of expr tree annihilated" )

## ◆ STATISTIC() [3/3]

 STATISTIC ( NumFactor , "Number of multiplies factored" )