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[ValueTracking] refactor: extract method haveNoCommonBitsSet 

Summary:
Extract method haveNoCommonBitsSet so that we don't have to duplicate this logic in
InstCombine and SeparateConstOffsetFromGEP.

This patch also makes SeparateConstOffsetFromGEP more precise by passing
DominatorTree to computeKnownBits.

Test Plan: value-tracking-domtree.ll that tests ValueTracking indeed leverages dominating conditions

Reviewers: broune, meheff, majnemer

Reviewed By: majnemer

Subscribers: jholewinski, llvm-commits

Differential Revision: http://reviews.llvm.org/D9734

llvm-svn: 237407
This commit is contained in:
Jingyue Wu 2015-05-14 23:53:19 +00:00
parent e9bcddd5cb
commit ca32190379
5 changed files with 100 additions and 71 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
llvm/include/llvm/Analysis/ValueTracking.h
View File

@ -47,6 +47,11 @@ namespace llvm {
/// \p KnownZero the set of bits that are known to be zero
void computeKnownBitsFromRangeMetadata(const MDNode &Ranges,
APInt &KnownZero);
/// Returns true if LHS and RHS have no common bits set.
bool haveNoCommonBitsSet(Value *LHS, Value *RHS, const DataLayout &DL,
AssumptionCache *AC = nullptr,
const Instruction *CxtI = nullptr,
const DominatorTree *DT = nullptr);
/// ComputeSignBit - Determine whether the sign bit is known to be zero or
/// one. Convenience wrapper around computeKnownBits.

15
llvm/lib/Analysis/ValueTracking.cpp
View File

@ -138,6 +138,21 @@ void llvm::computeKnownBits(Value *V, APInt &KnownZero, APInt &KnownOne,
Query(AC, safeCxtI(V, CxtI), DT));
}
bool llvm::haveNoCommonBitsSet(Value *LHS, Value *RHS, const DataLayout &DL,
AssumptionCache *AC, const Instruction *CxtI,
const DominatorTree *DT) {
assert(LHS->getType() == RHS->getType() &&
"LHS and RHS should have the same type");
assert(LHS->getType()->isIntOrIntVectorTy() &&
"LHS and RHS should be integers");
IntegerType *IT = cast<IntegerType>(LHS->getType()->getScalarType());
APInt LHSKnownZero(IT->getBitWidth(), 0), LHSKnownOne(IT->getBitWidth(), 0);
APInt RHSKnownZero(IT->getBitWidth(), 0), RHSKnownOne(IT->getBitWidth(), 0);
computeKnownBits(LHS, LHSKnownZero, LHSKnownOne, DL, 0, AC, CxtI, DT);
computeKnownBits(RHS, RHSKnownZero, RHSKnownOne, DL, 0, AC, CxtI, DT);
return (LHSKnownZero | RHSKnownZero).isAllOnesValue();
}
static void ComputeSignBit(Value *V, bool &KnownZero, bool &KnownOne,
const DataLayout &DL, unsigned Depth,
const Query &Q);

16
llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
View File

@ -1160,20 +1160,8 @@ Instruction *InstCombiner::visitAdd(BinaryOperator &I) {
return ReplaceInstUsesWith(I, V);
// A+B --> A|B iff A and B have no bits set in common.
if (IntegerType *IT = dyn_cast<IntegerType>(I.getType())) {
APInt LHSKnownOne(IT->getBitWidth(), 0);
APInt LHSKnownZero(IT->getBitWidth(), 0);
computeKnownBits(LHS, LHSKnownZero, LHSKnownOne, 0, &I);
if (LHSKnownZero != 0) {
APInt RHSKnownOne(IT->getBitWidth(), 0);
APInt RHSKnownZero(IT->getBitWidth(), 0);
computeKnownBits(RHS, RHSKnownZero, RHSKnownOne, 0, &I);
// No bits in common -> bitwise or.
if ((LHSKnownZero|RHSKnownZero).isAllOnesValue())
return BinaryOperator::CreateOr(LHS, RHS);
}
}
if (haveNoCommonBitsSet(LHS, RHS, DL, AC, &I, DT))
return BinaryOperator::CreateOr(LHS, RHS);
if (Constant *CRHS = dyn_cast<Constant>(RHS)) {
Value *X;

102
llvm/lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp
View File

@ -160,6 +160,7 @@
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Module.h"
@ -202,7 +203,7 @@ namespace {
/// 5); nor can we transform (3 * (a + 5)) to (3 * a + 5), however in this case,
/// -instcombine probably already optimized (3 * (a + 5)) to (3 * a + 15).
class ConstantOffsetExtractor {
public:
public:
/// Extracts a constant offset from the given GEP index. It returns the
/// new index representing the remainder (equal to the original index minus
/// the constant offset), or nullptr if we cannot extract a constant offset.
@ -210,15 +211,18 @@ class ConstantOffsetExtractor {
/// \p GEP The given GEP
/// \p UserChainTail Outputs the tail of UserChain so that we can
/// garbage-collect unused instructions in UserChain.
static Value *Extract(Value *Idx, GetElementPtrInst *GEP,
User *&UserChainTail);
static Value *Extract(Value *Idx, GetElementPtrInst *GEP,
User *&UserChainTail, const DominatorTree *DT);
/// Looks for a constant offset from the given GEP index without extracting
/// it. It returns the numeric value of the extracted constant offset (0 if
/// failed). The meaning of the arguments are the same as Extract.
static int64_t Find(Value *Idx, GetElementPtrInst *GEP);
static int64_t Find(Value *Idx, GetElementPtrInst *GEP,
const DominatorTree *DT);
private:
ConstantOffsetExtractor(Instruction *InsertionPt) : IP(InsertionPt) {}
private:
ConstantOffsetExtractor(Instruction *InsertionPt, const DominatorTree *DT)
: IP(InsertionPt), DL(InsertionPt->getModule()->getDataLayout()), DT(DT) {
}
/// Searches the expression that computes V for a non-zero constant C s.t.
/// V can be reassociated into the form V' + C. If the searching is
/// successful, returns C and update UserChain as a def-use chain from C to V;
@ -276,13 +280,6 @@ class ConstantOffsetExtractor {
/// returns "sext i32 (zext i16 V to i32) to i64".
Value *applyExts(Value *V);
/// Returns true if LHS and RHS have no bits in common, i.e., for every n
/// the n-th bit of either LHS, or RHS is 0.
bool NoCommonBits(Value *LHS, Value *RHS) const;
/// Computes which bits are known to be one or zero.
/// \p KnownOne Mask of all bits that are known to be one.
/// \p KnownZero Mask of all bits that are known to be zero.
void ComputeKnownBits(Value *V, APInt &KnownOne, APInt &KnownZero) const;
/// A helper function that returns whether we can trace into the operands
/// of binary operator BO for a constant offset.
///
@ -304,28 +301,35 @@ class ConstantOffsetExtractor {
/// sext/zext instructions along UserChain.
SmallVector<CastInst *, 16> ExtInsts;
Instruction *IP; /// Insertion position of cloned instructions.
const DataLayout &DL;
const DominatorTree *DT;
};
/// \brief A pass that tries to split every GEP in the function into a variadic
/// base and a constant offset. It is a FunctionPass because searching for the
/// constant offset may inspect other basic blocks.
class SeparateConstOffsetFromGEP : public FunctionPass {
public:
public:
static char ID;
SeparateConstOffsetFromGEP(const TargetMachine *TM = nullptr,
bool LowerGEP = false)
: FunctionPass(ID), TM(TM), LowerGEP(LowerGEP) {
: FunctionPass(ID), DL(nullptr), DT(nullptr), TM(TM), LowerGEP(LowerGEP) {
initializeSeparateConstOffsetFromGEPPass(*PassRegistry::getPassRegistry());
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<DominatorTreeWrapperPass>();
AU.addRequired<TargetTransformInfoWrapperPass>();
AU.setPreservesCFG();
}
bool doInitialization(Module &M) override {
DL = &M.getDataLayout();
return false;
}
bool runOnFunction(Function &F) override;
private:
private:
/// Tries to split the given GEP into a variadic base and a constant offset,
/// and returns true if the splitting succeeds.
bool splitGEP(GetElementPtrInst *GEP);
@ -372,6 +376,8 @@ class SeparateConstOffsetFromGEP : public FunctionPass {
/// Verify F is free of dead code.
void verifyNoDeadCode(Function &F);
const DataLayout *DL;
const DominatorTree *DT;
const TargetMachine *TM;
/// Whether to lower a GEP with multiple indices into arithmetic operations or
/// multiple GEPs with a single index.
@ -384,6 +390,7 @@ INITIALIZE_PASS_BEGIN(
SeparateConstOffsetFromGEP, "separate-const-offset-from-gep",
"Split GEPs to a variadic base and a constant offset for better CSE", false,
false)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
INITIALIZE_PASS_END(
SeparateConstOffsetFromGEP, "separate-const-offset-from-gep",
@ -412,7 +419,8 @@ bool ConstantOffsetExtractor::CanTraceInto(bool SignExtended,
Value *LHS = BO->getOperand(0), *RHS = BO->getOperand(1);
// Do not trace into "or" unless it is equivalent to "add". If LHS and RHS
// don't have common bits, (LHS | RHS) is equivalent to (LHS + RHS).
if (BO->getOpcode() == Instruction::Or && !NoCommonBits(LHS, RHS))
if (BO->getOpcode() == Instruction::Or &&
!haveNoCommonBitsSet(LHS, RHS, DL, nullptr, BO, DT))
return false;
// In addition, tracing into BO requires that its surrounding s/zext (if
@ -497,9 +505,8 @@ APInt ConstantOffsetExtractor::find(Value *V, bool SignExtended,
ConstantOffset = CI->getValue();
} else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(V)) {
// Trace into subexpressions for more hoisting opportunities.
if (CanTraceInto(SignExtended, ZeroExtended, BO, NonNegative)) {
if (CanTraceInto(SignExtended, ZeroExtended, BO, NonNegative))
ConstantOffset = findInEitherOperand(BO, SignExtended, ZeroExtended);
}
} else if (isa<SExtInst>(V)) {
ConstantOffset = find(U->getOperand(0), /* SignExtended */ true,
ZeroExtended, NonNegative).sext(BitWidth);
@ -642,8 +649,9 @@ Value *ConstantOffsetExtractor::removeConstOffset(unsigned ChainIndex) {
}
Value *ConstantOffsetExtractor::Extract(Value *Idx, GetElementPtrInst *GEP,
User *&UserChainTail) {
ConstantOffsetExtractor Extractor(GEP);
User *&UserChainTail,
const DominatorTree *DT) {
ConstantOffsetExtractor Extractor(GEP, DT);
// Find a non-zero constant offset first.
APInt ConstantOffset =
Extractor.find(Idx, /* SignExtended */ false, /* ZeroExtended */ false,
@ -658,37 +666,19 @@ Value *ConstantOffsetExtractor::Extract(Value *Idx, GetElementPtrInst *GEP,
return IdxWithoutConstOffset;
}
int64_t ConstantOffsetExtractor::Find(Value *Idx, GetElementPtrInst *GEP) {
int64_t ConstantOffsetExtractor::Find(Value *Idx, GetElementPtrInst *GEP,
const DominatorTree *DT) {
// If Idx is an index of an inbound GEP, Idx is guaranteed to be non-negative.
return ConstantOffsetExtractor(GEP)
return ConstantOffsetExtractor(GEP, DT)
.find(Idx, /* SignExtended */ false, /* ZeroExtended */ false,
GEP->isInBounds())
.getSExtValue();
}
void ConstantOffsetExtractor::ComputeKnownBits(Value *V, APInt &KnownOne,
APInt &KnownZero) const {
IntegerType *IT = cast<IntegerType>(V->getType());
KnownOne = APInt(IT->getBitWidth(), 0);
KnownZero = APInt(IT->getBitWidth(), 0);
const DataLayout &DL = IP->getModule()->getDataLayout();
llvm::computeKnownBits(V, KnownZero, KnownOne, DL, 0);
}
bool ConstantOffsetExtractor::NoCommonBits(Value *LHS, Value *RHS) const {
assert(LHS->getType() == RHS->getType() &&
"LHS and RHS should have the same type");
APInt LHSKnownOne, LHSKnownZero, RHSKnownOne, RHSKnownZero;
ComputeKnownBits(LHS, LHSKnownOne, LHSKnownZero);
ComputeKnownBits(RHS, RHSKnownOne, RHSKnownZero);
return (LHSKnownZero | RHSKnownZero).isAllOnesValue();
}
bool SeparateConstOffsetFromGEP::canonicalizeArrayIndicesToPointerSize(
GetElementPtrInst *GEP) {
bool Changed = false;
const DataLayout &DL = GEP->getModule()->getDataLayout();
Type *IntPtrTy = DL.getIntPtrType(GEP->getType());
Type *IntPtrTy = DL->getIntPtrType(GEP->getType());
gep_type_iterator GTI = gep_type_begin(*GEP);
for (User::op_iterator I = GEP->op_begin() + 1, E = GEP->op_end();
I != E; ++I, ++GTI) {
@ -709,19 +699,18 @@ SeparateConstOffsetFromGEP::accumulateByteOffset(GetElementPtrInst *GEP,
NeedsExtraction = false;
int64_t AccumulativeByteOffset = 0;
gep_type_iterator GTI = gep_type_begin(*GEP);
const DataLayout &DL = GEP->getModule()->getDataLayout();
for (unsigned I = 1, E = GEP->getNumOperands(); I != E; ++I, ++GTI) {
if (isa<SequentialType>(*GTI)) {
// Tries to extract a constant offset from this GEP index.
int64_t ConstantOffset =
ConstantOffsetExtractor::Find(GEP->getOperand(I), GEP);
ConstantOffsetExtractor::Find(GEP->getOperand(I), GEP, DT);
if (ConstantOffset != 0) {
NeedsExtraction = true;
// A GEP may have multiple indices. We accumulate the extracted
// constant offset to a byte offset, and later offset the remainder of
// the original GEP with this byte offset.
AccumulativeByteOffset +=
ConstantOffset * DL.getTypeAllocSize(GTI.getIndexedType());
ConstantOffset * DL->getTypeAllocSize(GTI.getIndexedType());
}
} else if (LowerGEP) {
StructType *StTy = cast<StructType>(*GTI);
@ -730,7 +719,7 @@ SeparateConstOffsetFromGEP::accumulateByteOffset(GetElementPtrInst *GEP,
if (Field != 0) {
NeedsExtraction = true;
AccumulativeByteOffset +=
DL.getStructLayout(StTy)->getElementOffset(Field);
DL->getStructLayout(StTy)->getElementOffset(Field);
}
}
}
@ -740,8 +729,7 @@ SeparateConstOffsetFromGEP::accumulateByteOffset(GetElementPtrInst *GEP,
void SeparateConstOffsetFromGEP::lowerToSingleIndexGEPs(
GetElementPtrInst *Variadic, int64_t AccumulativeByteOffset) {
IRBuilder<> Builder(Variadic);
const DataLayout &DL = Variadic->getModule()->getDataLayout();
Type *IntPtrTy = DL.getIntPtrType(Variadic->getType());
Type *IntPtrTy = DL->getIntPtrType(Variadic->getType());
Type *I8PtrTy =
Builder.getInt8PtrTy(Variadic->getType()->getPointerAddressSpace());
@ -761,7 +749,7 @@ void SeparateConstOffsetFromGEP::lowerToSingleIndexGEPs(
continue;
APInt ElementSize = APInt(IntPtrTy->getIntegerBitWidth(),
DL.getTypeAllocSize(GTI.getIndexedType()));
DL->getTypeAllocSize(GTI.getIndexedType()));
// Scale the index by element size.
if (ElementSize != 1) {
if (ElementSize.isPowerOf2()) {
@ -794,8 +782,7 @@ void
SeparateConstOffsetFromGEP::lowerToArithmetics(GetElementPtrInst *Variadic,
int64_t AccumulativeByteOffset) {
IRBuilder<> Builder(Variadic);
const DataLayout &DL = Variadic->getModule()->getDataLayout();
Type *IntPtrTy = DL.getIntPtrType(Variadic->getType());
Type *IntPtrTy = DL->getIntPtrType(Variadic->getType());
Value *ResultPtr = Builder.CreatePtrToInt(Variadic->getOperand(0), IntPtrTy);
gep_type_iterator GTI = gep_type_begin(*Variadic);
@ -811,7 +798,7 @@ SeparateConstOffsetFromGEP::lowerToArithmetics(GetElementPtrInst *Variadic,
continue;
APInt ElementSize = APInt(IntPtrTy->getIntegerBitWidth(),
DL.getTypeAllocSize(GTI.getIndexedType()));
DL->getTypeAllocSize(GTI.getIndexedType()));
// Scale the index by element size.
if (ElementSize != 1) {
if (ElementSize.isPowerOf2()) {
@ -887,7 +874,7 @@ bool SeparateConstOffsetFromGEP::splitGEP(GetElementPtrInst *GEP) {
Value *OldIdx = GEP->getOperand(I);
User *UserChainTail;
Value *NewIdx =
ConstantOffsetExtractor::Extract(OldIdx, GEP, UserChainTail);
ConstantOffsetExtractor::Extract(OldIdx, GEP, UserChainTail, DT);
if (NewIdx != nullptr) {
// Switches to the index with the constant offset removed.
GEP->setOperand(I, NewIdx);
@ -969,10 +956,9 @@ bool SeparateConstOffsetFromGEP::splitGEP(GetElementPtrInst *GEP) {
// Per ANSI C standard, signed / unsigned = unsigned and signed % unsigned =
// unsigned.. Therefore, we cast ElementTypeSizeOfGEP to signed because it is
// used with unsigned integers later.
const DataLayout &DL = GEP->getModule()->getDataLayout();
int64_t ElementTypeSizeOfGEP = static_cast<int64_t>(
DL.getTypeAllocSize(GEP->getType()->getElementType()));
Type *IntPtrTy = DL.getIntPtrType(GEP->getType());
DL->getTypeAllocSize(GEP->getType()->getElementType()));
Type *IntPtrTy = DL->getIntPtrType(GEP->getType());
if (AccumulativeByteOffset % ElementTypeSizeOfGEP == 0) {
// Very likely. As long as %gep is natually aligned, the byte offset we
// extracted should be a multiple of sizeof(*%gep).
@ -1019,6 +1005,8 @@ bool SeparateConstOffsetFromGEP::runOnFunction(Function &F) {
if (DisableSeparateConstOffsetFromGEP)
return false;
DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
bool Changed = false;
for (Function::iterator B = F.begin(), BE = F.end(); B != BE; ++B) {
for (BasicBlock::iterator I = B->begin(), IE = B->end(); I != IE; ) {

33
llvm/test/Transforms/SeparateConstOffsetFromGEP/NVPTX/value-tracking-domtree.ll Normal file
View File

@ -0,0 +1,33 @@
; RUN: opt < %s -separate-const-offset-from-gep -value-tracking-dom-conditions -reassociate-geps-verify-no-dead-code -S | FileCheck %s
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "nvptx64-unknown-unknown"
; if (i == 4)
; p = &input[i | 3];
;
; =>
;
; if (i == 4) {
; base = &input[i];
; p = &base[3];
; }
;
; We should treat (i | 3) as (i + 3) because i is guaranteed to be 4, which
; does not share any set bits with 3.
define float* @guarded_or(float* %input, i64 %i) {
; CHECK-LABEL: @guarded_or(
entry:
%is4 = icmp eq i64 %i, 4
br i1 %is4, label %then, label %exit
then:
%or = or i64 %i, 3
%p = getelementptr inbounds float, float* %input, i64 %or
; CHECK: [[base:[^ ]+]] = getelementptr float, float* %input, i64 %i
; CHECK: getelementptr float, float* [[base]], i64 3
ret float* %p
exit:
ret float* null
}