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//===- CmpInstAnalysis.cpp - Utils to help fold compares ---------------===//
//
// 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 file holds routines to help analyse compare instructions
// and fold them into constants or other compare instructions
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/CmpInstAnalysis.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/PatternMatch.h"
using namespace llvm;
unsigned llvm::getICmpCode(CmpInst::Predicate Pred) {
switch (Pred) {
// False -> 0
case ICmpInst::ICMP_UGT: return 1; // 001
case ICmpInst::ICMP_SGT: return 1; // 001
case ICmpInst::ICMP_EQ: return 2; // 010
case ICmpInst::ICMP_UGE: return 3; // 011
case ICmpInst::ICMP_SGE: return 3; // 011
case ICmpInst::ICMP_ULT: return 4; // 100
case ICmpInst::ICMP_SLT: return 4; // 100
case ICmpInst::ICMP_NE: return 5; // 101
case ICmpInst::ICMP_ULE: return 6; // 110
case ICmpInst::ICMP_SLE: return 6; // 110
// True -> 7
default:
llvm_unreachable("Invalid ICmp predicate!");
}
}
Constant *llvm::getPredForICmpCode(unsigned Code, bool Sign, Type *OpTy,
CmpInst::Predicate &Pred) {
switch (Code) {
default: llvm_unreachable("Illegal ICmp code!");
case 0: // False.
return ConstantInt::get(CmpInst::makeCmpResultType(OpTy), 0);
case 1: Pred = Sign ? ICmpInst::ICMP_SGT : ICmpInst::ICMP_UGT; break;
case 2: Pred = ICmpInst::ICMP_EQ; break;
case 3: Pred = Sign ? ICmpInst::ICMP_SGE : ICmpInst::ICMP_UGE; break;
case 4: Pred = Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT; break;
case 5: Pred = ICmpInst::ICMP_NE; break;
case 6: Pred = Sign ? ICmpInst::ICMP_SLE : ICmpInst::ICMP_ULE; break;
case 7: // True.
return ConstantInt::get(CmpInst::makeCmpResultType(OpTy), 1);
}
return nullptr;
}
bool llvm::predicatesFoldable(ICmpInst::Predicate P1, ICmpInst::Predicate P2) {
return (CmpInst::isSigned(P1) == CmpInst::isSigned(P2)) ||
(CmpInst::isSigned(P1) && ICmpInst::isEquality(P2)) ||
(CmpInst::isSigned(P2) && ICmpInst::isEquality(P1));
}
Constant *llvm::getPredForFCmpCode(unsigned Code, Type *OpTy,
CmpInst::Predicate &Pred) {
Pred = static_cast<FCmpInst::Predicate>(Code);
assert(FCmpInst::FCMP_FALSE <= Pred && Pred <= FCmpInst::FCMP_TRUE &&
"Unexpected FCmp predicate!");
if (Pred == FCmpInst::FCMP_FALSE)
return ConstantInt::get(CmpInst::makeCmpResultType(OpTy), 0);
if (Pred == FCmpInst::FCMP_TRUE)
return ConstantInt::get(CmpInst::makeCmpResultType(OpTy), 1);
return nullptr;
}
std::optional<DecomposedBitTest>
llvm::decomposeBitTestICmp(Value *LHS, Value *RHS, CmpInst::Predicate Pred,
bool LookThruTrunc, bool AllowNonZeroC,
bool DecomposeAnd) {
using namespace PatternMatch;
const APInt *OrigC;
if ((ICmpInst::isEquality(Pred) && !DecomposeAnd) ||
!match(RHS, m_APIntAllowPoison(OrigC)))
return std::nullopt;
bool Inverted = false;
if (ICmpInst::isGT(Pred) || ICmpInst::isGE(Pred)) {
Inverted = true;
Pred = ICmpInst::getInversePredicate(Pred);
}
APInt C = *OrigC;
if (ICmpInst::isLE(Pred)) {
if (ICmpInst::isSigned(Pred) ? C.isMaxSignedValue() : C.isMaxValue())
return std::nullopt;
++C;
Pred = ICmpInst::getStrictPredicate(Pred);
}
DecomposedBitTest Result;
switch (Pred) {
default:
llvm_unreachable("Unexpected predicate");
case ICmpInst::ICMP_SLT: {
// X < 0 is equivalent to (X & SignMask) != 0.
if (C.isZero()) {
Result.Mask = APInt::getSignMask(C.getBitWidth());
Result.C = APInt::getZero(C.getBitWidth());
Result.Pred = ICmpInst::ICMP_NE;
break;
}
APInt FlippedSign = C ^ APInt::getSignMask(C.getBitWidth());
if (FlippedSign.isPowerOf2()) {
// X s< 10000100 is equivalent to (X & 11111100 == 10000000)
Result.Mask = -FlippedSign;
Result.C = APInt::getSignMask(C.getBitWidth());
Result.Pred = ICmpInst::ICMP_EQ;
break;
}
if (FlippedSign.isNegatedPowerOf2()) {
// X s< 01111100 is equivalent to (X & 11111100 != 01111100)
Result.Mask = FlippedSign;
Result.C = C;
Result.Pred = ICmpInst::ICMP_NE;
break;
}
return std::nullopt;
}
case ICmpInst::ICMP_ULT: {
// X <u 2^n is equivalent to (X & ~(2^n-1)) == 0.
if (C.isPowerOf2()) {
Result.Mask = -C;
Result.C = APInt::getZero(C.getBitWidth());
Result.Pred = ICmpInst::ICMP_EQ;
break;
}
// X u< 11111100 is equivalent to (X & 11111100 != 11111100)
if (C.isNegatedPowerOf2()) {
Result.Mask = C;
Result.C = C;
Result.Pred = ICmpInst::ICMP_NE;
break;
}
return std::nullopt;
}
case ICmpInst::ICMP_EQ:
case ICmpInst::ICMP_NE: {
assert(DecomposeAnd);
const APInt *AndC;
Value *AndVal;
if (match(LHS, m_And(m_Value(AndVal), m_APIntAllowPoison(AndC)))) {
LHS = AndVal;
Result.Mask = *AndC;
Result.C = C;
Result.Pred = Pred;
break;
}
return std::nullopt;
}
}
if (!AllowNonZeroC && !Result.C.isZero())
return std::nullopt;
if (Inverted)
Result.Pred = ICmpInst::getInversePredicate(Result.Pred);
Value *X;
if (LookThruTrunc && match(LHS, m_Trunc(m_Value(X)))) {
Result.X = X;
Result.Mask = Result.Mask.zext(X->getType()->getScalarSizeInBits());
Result.C = Result.C.zext(X->getType()->getScalarSizeInBits());
} else {
Result.X = LHS;
}
return Result;
}
std::optional<DecomposedBitTest> llvm::decomposeBitTest(Value *Cond,
bool LookThruTrunc,
bool AllowNonZeroC,
bool DecomposeAnd) {
using namespace PatternMatch;
if (auto *ICmp = dyn_cast<ICmpInst>(Cond)) {
// Don't allow pointers. Splat vectors are fine.
if (!ICmp->getOperand(0)->getType()->isIntOrIntVectorTy())
return std::nullopt;
return decomposeBitTestICmp(ICmp->getOperand(0), ICmp->getOperand(1),
ICmp->getPredicate(), LookThruTrunc,
AllowNonZeroC, DecomposeAnd);
}
Value *X;
if (Cond->getType()->isIntOrIntVectorTy(1) &&
(match(Cond, m_Trunc(m_Value(X))) ||
match(Cond, m_Not(m_Trunc(m_Value(X)))))) {
DecomposedBitTest Result;
Result.X = X;
unsigned BitWidth = X->getType()->getScalarSizeInBits();
Result.Mask = APInt(BitWidth, 1);
Result.C = APInt::getZero(BitWidth);
Result.Pred = isa<TruncInst>(Cond) ? ICmpInst::ICMP_NE : ICmpInst::ICMP_EQ;
return Result;
}
return std::nullopt;
}
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