llvm/lib/Analysis/OverflowInstAnalysis.cpp

   1 //==-- OverflowInstAnalysis.cpp - Utils to fold overflow insts ----*- C++ -*-=//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This file holds routines to help analyse overflow instructions
  10 // and fold them into constants or other overflow instructions
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "llvm/Analysis/OverflowInstAnalysis.h"
  15 #include "llvm/IR/Constants.h"
  16 #include "llvm/IR/Instructions.h"
  17 #include "llvm/IR/PatternMatch.h"
  18
  19 using namespace llvm;
  20 using namespace llvm::PatternMatch;
  21
  22 bool llvm::isCheckForZeroAndMulWithOverflow(Value *Op0, Value *Op1, bool IsAnd,
  23                                             Use *&Y) {
  24   ICmpInst::Predicate Pred;
  25   Value *X, *NotOp1;
  26   int XIdx;
  27   IntrinsicInst *II;
  28
  29   if (!match(Op0, m_ICmp(Pred, m_Value(X), m_Zero())))
  30     return false;
  31
  32   ///   %Agg = call { i4, i1 } @llvm.[us]mul.with.overflow.i4(i4 %X, i4 %???)
  33   ///   %V = extractvalue { i4, i1 } %Agg, 1
  34   auto matchMulOverflowCheck = [X, &II, &XIdx](Value *V) {
  35     auto *Extract = dyn_cast<ExtractValueInst>(V);
  36     // We should only be extracting the overflow bit.
  37     if (!Extract || !Extract->getIndices().equals(1))
  38       return false;
  39
  40     II = dyn_cast<IntrinsicInst>(Extract->getAggregateOperand());
  41     if (!II ||
  42         !match(II, m_CombineOr(m_Intrinsic<Intrinsic::umul_with_overflow>(),
  43                                m_Intrinsic<Intrinsic::smul_with_overflow>())))
  44       return false;
  45
  46     if (II->getArgOperand(0) == X)
  47       XIdx = 0;
  48     else if (II->getArgOperand(1) == X)
  49       XIdx = 1;
  50     else
  51       return false;
  52     return true;
  53   };
  54
  55   bool Matched =
  56       (IsAnd && Pred == ICmpInst::Predicate::ICMP_NE &&
  57        matchMulOverflowCheck(Op1)) ||
  58       (!IsAnd && Pred == ICmpInst::Predicate::ICMP_EQ &&
  59        match(Op1, m_Not(m_Value(NotOp1))) && matchMulOverflowCheck(NotOp1));
  60
  61   if (!Matched)
  62     return false;
  63
  64   Y = &II->getArgOperandUse(!XIdx);
  65   return true;
  66 }
  67
  68 bool llvm::isCheckForZeroAndMulWithOverflow(Value *Op0, Value *Op1,
  69                                             bool IsAnd) {
  70   Use *Y;
  71   return isCheckForZeroAndMulWithOverflow(Op0, Op1, IsAnd, Y);
  72 }