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97 lines
3.8 KiB
C++
97 lines
3.8 KiB
C++
//===- CmpInstAnalysis.cpp - Utils to help fold compares ---------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file holds routines to help analyse compare instructions
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// and fold them into constants or other compare instructions
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/Utils/CmpInstAnalysis.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/Instructions.h"
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using namespace llvm;
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/// getICmpCode - Encode a icmp predicate into a three bit mask. These bits
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/// are carefully arranged to allow folding of expressions such as:
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///
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/// (A < B) | (A > B) --> (A != B)
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///
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/// Note that this is only valid if the first and second predicates have the
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/// same sign. Is illegal to do: (A u< B) | (A s> B)
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///
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/// Three bits are used to represent the condition, as follows:
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/// 0 A > B
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/// 1 A == B
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/// 2 A < B
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///
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/// <=> Value Definition
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/// 000 0 Always false
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/// 001 1 A > B
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/// 010 2 A == B
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/// 011 3 A >= B
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/// 100 4 A < B
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/// 101 5 A != B
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/// 110 6 A <= B
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/// 111 7 Always true
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///
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unsigned llvm::getICmpCode(const ICmpInst *ICI, bool InvertPred) {
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ICmpInst::Predicate Pred = InvertPred ? ICI->getInversePredicate()
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: ICI->getPredicate();
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switch (Pred) {
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// False -> 0
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case ICmpInst::ICMP_UGT: return 1; // 001
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case ICmpInst::ICMP_SGT: return 1; // 001
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case ICmpInst::ICMP_EQ: return 2; // 010
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case ICmpInst::ICMP_UGE: return 3; // 011
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case ICmpInst::ICMP_SGE: return 3; // 011
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case ICmpInst::ICMP_ULT: return 4; // 100
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case ICmpInst::ICMP_SLT: return 4; // 100
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case ICmpInst::ICMP_NE: return 5; // 101
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case ICmpInst::ICMP_ULE: return 6; // 110
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case ICmpInst::ICMP_SLE: return 6; // 110
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// True -> 7
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default:
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llvm_unreachable("Invalid ICmp predicate!");
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}
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}
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/// getICmpValue - This is the complement of getICmpCode, which turns an
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/// opcode and two operands into either a constant true or false, or the
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/// predicate for a new ICmp instruction. The sign is passed in to determine
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/// which kind of predicate to use in the new icmp instruction.
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/// Non-NULL return value will be a true or false constant.
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/// NULL return means a new ICmp is needed. The predicate for which is
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/// output in NewICmpPred.
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Value *llvm::getICmpValue(bool Sign, unsigned Code, Value *LHS, Value *RHS,
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CmpInst::Predicate &NewICmpPred) {
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switch (Code) {
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default: llvm_unreachable("Illegal ICmp code!");
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case 0: // False.
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return ConstantInt::get(CmpInst::makeCmpResultType(LHS->getType()), 0);
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case 1: NewICmpPred = Sign ? ICmpInst::ICMP_SGT : ICmpInst::ICMP_UGT; break;
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case 2: NewICmpPred = ICmpInst::ICMP_EQ; break;
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case 3: NewICmpPred = Sign ? ICmpInst::ICMP_SGE : ICmpInst::ICMP_UGE; break;
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case 4: NewICmpPred = Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT; break;
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case 5: NewICmpPred = ICmpInst::ICMP_NE; break;
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case 6: NewICmpPred = Sign ? ICmpInst::ICMP_SLE : ICmpInst::ICMP_ULE; break;
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case 7: // True.
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return ConstantInt::get(CmpInst::makeCmpResultType(LHS->getType()), 1);
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}
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return nullptr;
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}
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/// PredicatesFoldable - Return true if both predicates match sign or if at
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/// least one of them is an equality comparison (which is signless).
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bool llvm::PredicatesFoldable(ICmpInst::Predicate p1, ICmpInst::Predicate p2) {
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return (CmpInst::isSigned(p1) == CmpInst::isSigned(p2)) ||
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(CmpInst::isSigned(p1) && ICmpInst::isEquality(p2)) ||
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(CmpInst::isSigned(p2) && ICmpInst::isEquality(p1));
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}
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