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Diffstat (limited to 'lib/Transforms/Utils/CmpInstAnalysis.cpp')
| -rw-r--r-- | lib/Transforms/Utils/CmpInstAnalysis.cpp | 96 |
1 files changed, 96 insertions, 0 deletions
diff --git a/lib/Transforms/Utils/CmpInstAnalysis.cpp b/lib/Transforms/Utils/CmpInstAnalysis.cpp new file mode 100644 index 0000000..9b09915 --- /dev/null +++ b/lib/Transforms/Utils/CmpInstAnalysis.cpp @@ -0,0 +1,96 @@ +//===- CmpInstAnalysis.cpp - Utils to help fold compares ---------------===// +// +// The LLVM Compiler Infrastructure +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +// +// This file holds routines to help analyse compare instructions +// and fold them into constants or other compare instructions +// +//===----------------------------------------------------------------------===// + +#include "llvm/Transforms/Utils/CmpInstAnalysis.h" +#include "llvm/Constants.h" +#include "llvm/Instructions.h" + +using namespace llvm; + +/// getICmpCode - Encode a icmp predicate into a three bit mask. These bits +/// are carefully arranged to allow folding of expressions such as: +/// +/// (A < B) | (A > B) --> (A != B) +/// +/// Note that this is only valid if the first and second predicates have the +/// same sign. Is illegal to do: (A u< B) | (A s> B) +/// +/// Three bits are used to represent the condition, as follows: +/// 0 A > B +/// 1 A == B +/// 2 A < B +/// +/// <=> Value Definition +/// 000 0 Always false +/// 001 1 A > B +/// 010 2 A == B +/// 011 3 A >= B +/// 100 4 A < B +/// 101 5 A != B +/// 110 6 A <= B +/// 111 7 Always true +/// +unsigned llvm::getICmpCode(const ICmpInst *ICI, bool InvertPred) { + ICmpInst::Predicate Pred = InvertPred ? ICI->getInversePredicate() + : ICI->getPredicate(); + 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!"); + } +} + +/// getICmpValue - This is the complement of getICmpCode, which turns an +/// opcode and two operands into either a constant true or false, or the +/// predicate for a new ICmp instruction. The sign is passed in to determine +/// which kind of predicate to use in the new icmp instruction. +/// Non-NULL return value will be a true or false constant. +/// NULL return means a new ICmp is needed. The predicate for which is +/// output in NewICmpPred. +Value *llvm::getICmpValue(bool Sign, unsigned Code, Value *LHS, Value *RHS, + CmpInst::Predicate &NewICmpPred) { + switch (Code) { + default: llvm_unreachable("Illegal ICmp code!"); + case 0: // False. + return ConstantInt::get(CmpInst::makeCmpResultType(LHS->getType()), 0); + case 1: NewICmpPred = Sign ? ICmpInst::ICMP_SGT : ICmpInst::ICMP_UGT; break; + case 2: NewICmpPred = ICmpInst::ICMP_EQ; break; + case 3: NewICmpPred = Sign ? ICmpInst::ICMP_SGE : ICmpInst::ICMP_UGE; break; + case 4: NewICmpPred = Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT; break; + case 5: NewICmpPred = ICmpInst::ICMP_NE; break; + case 6: NewICmpPred = Sign ? ICmpInst::ICMP_SLE : ICmpInst::ICMP_ULE; break; + case 7: // True. + return ConstantInt::get(CmpInst::makeCmpResultType(LHS->getType()), 1); + } + return NULL; +} + +/// PredicatesFoldable - Return true if both predicates match sign or if at +/// least one of them is an equality comparison (which is signless). +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)); +} |
