125 lines
5.1 KiB
C++
125 lines
5.1 KiB
C++
//===-- CmpInstAnalysis.h - Utils to help fold compare insts ----*- C++ -*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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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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#ifndef LLVM_ANALYSIS_CMPINSTANALYSIS_H
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#define LLVM_ANALYSIS_CMPINSTANALYSIS_H
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#include "llvm/ADT/APInt.h"
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#include "llvm/IR/InstrTypes.h"
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namespace llvm {
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class Type;
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class Value;
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/// Encode a icmp predicate into a three bit mask. These bits are carefully
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/// 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. It 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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LLVM_ABI unsigned getICmpCode(CmpInst::Predicate Pred);
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/// This is the complement of getICmpCode. It turns a predicate code into
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/// either a constant true or false or the predicate for a new ICmp.
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/// The sign is passed in to determine which kind of predicate to use in the
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/// 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 is output in Pred.
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LLVM_ABI Constant *getPredForICmpCode(unsigned Code, bool Sign, Type *OpTy,
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CmpInst::Predicate &Pred);
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/// Return true if both predicates match sign or if at least one of them is an
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/// equality comparison (which is signless).
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LLVM_ABI bool predicatesFoldable(CmpInst::Predicate P1,
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CmpInst::Predicate P2);
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/// Similar to getICmpCode but for FCmpInst. This encodes a fcmp predicate
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/// into a four bit mask.
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inline unsigned getFCmpCode(CmpInst::Predicate CC) {
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assert(CmpInst::FCMP_FALSE <= CC && CC <= CmpInst::FCMP_TRUE &&
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"Unexpected FCmp predicate!");
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// Take advantage of the bit pattern of CmpInst::Predicate here.
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// U L G E
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static_assert(CmpInst::FCMP_FALSE == 0); // 0 0 0 0
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static_assert(CmpInst::FCMP_OEQ == 1); // 0 0 0 1
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static_assert(CmpInst::FCMP_OGT == 2); // 0 0 1 0
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static_assert(CmpInst::FCMP_OGE == 3); // 0 0 1 1
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static_assert(CmpInst::FCMP_OLT == 4); // 0 1 0 0
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static_assert(CmpInst::FCMP_OLE == 5); // 0 1 0 1
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static_assert(CmpInst::FCMP_ONE == 6); // 0 1 1 0
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static_assert(CmpInst::FCMP_ORD == 7); // 0 1 1 1
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static_assert(CmpInst::FCMP_UNO == 8); // 1 0 0 0
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static_assert(CmpInst::FCMP_UEQ == 9); // 1 0 0 1
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static_assert(CmpInst::FCMP_UGT == 10); // 1 0 1 0
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static_assert(CmpInst::FCMP_UGE == 11); // 1 0 1 1
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static_assert(CmpInst::FCMP_ULT == 12); // 1 1 0 0
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static_assert(CmpInst::FCMP_ULE == 13); // 1 1 0 1
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static_assert(CmpInst::FCMP_UNE == 14); // 1 1 1 0
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static_assert(CmpInst::FCMP_TRUE == 15); // 1 1 1 1
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return CC;
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}
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/// This is the complement of getFCmpCode. It turns a predicate code into
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/// either a constant true or false or the predicate for a new FCmp.
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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 is output in Pred.
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LLVM_ABI Constant *getPredForFCmpCode(unsigned Code, Type *OpTy,
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CmpInst::Predicate &Pred);
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/// Represents the operation icmp (X & Mask) pred C, where pred can only be
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/// eq or ne.
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struct DecomposedBitTest {
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Value *X;
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CmpInst::Predicate Pred;
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APInt Mask;
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APInt C;
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};
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/// Decompose an icmp into the form ((X & Mask) pred C) if possible.
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/// Unless \p AllowNonZeroC is true, C will always be 0. If \p
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/// DecomposeAnd is specified, then, for equality predicates, this will
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/// decompose bitmasking via `and`.
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LLVM_ABI std::optional<DecomposedBitTest>
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decomposeBitTestICmp(Value *LHS, Value *RHS, CmpInst::Predicate Pred,
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bool LookThroughTrunc = true, bool AllowNonZeroC = false,
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bool DecomposeAnd = false);
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/// Decompose an icmp into the form ((X & Mask) pred C) if
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/// possible. Unless \p AllowNonZeroC is true, C will always be 0.
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/// If \p DecomposeAnd is specified, then, for equality predicates, this
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/// will decompose bitmasking via `and`.
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LLVM_ABI std::optional<DecomposedBitTest>
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decomposeBitTest(Value *Cond, bool LookThroughTrunc = true,
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bool AllowNonZeroC = false, bool DecomposeAnd = false);
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} // end namespace llvm
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#endif
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