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/Instructions.h"
16 #include "llvm/IR/PatternMatch.h"
17 
18 using namespace llvm;
19 using namespace llvm::PatternMatch;
20 
21 bool llvm::isCheckForZeroAndMulWithOverflow(Value *Op0, Value *Op1, bool IsAnd,
22                                             Use *&Y) {
23   ICmpInst::Predicate Pred;
24   Value *X, *NotOp1;
25   int XIdx;
26   IntrinsicInst *II;
27 
28   if (!match(Op0, m_ICmp(Pred, m_Value(X), m_Zero())))
29     return false;
30 
31   ///   %Agg = call { i4, i1 } @llvm.[us]mul.with.overflow.i4(i4 %X, i4 %???)
32   ///   %V = extractvalue { i4, i1 } %Agg, 1
33   auto matchMulOverflowCheck = [X, &II, &XIdx](Value *V) {
34     auto *Extract = dyn_cast<ExtractValueInst>(V);
35     // We should only be extracting the overflow bit.
36     if (!Extract || !Extract->getIndices().equals(1))
37       return false;
38 
39     II = dyn_cast<IntrinsicInst>(Extract->getAggregateOperand());
40     if (!II ||
41         !match(II, m_CombineOr(m_Intrinsic<Intrinsic::umul_with_overflow>(),
42                                m_Intrinsic<Intrinsic::smul_with_overflow>())))
43       return false;
44 
45     if (II->getArgOperand(0) == X)
46       XIdx = 0;
47     else if (II->getArgOperand(1) == X)
48       XIdx = 1;
49     else
50       return false;
51     return true;
52   };
53 
54   bool Matched =
55       (IsAnd && Pred == ICmpInst::Predicate::ICMP_NE &&
56        matchMulOverflowCheck(Op1)) ||
57       (!IsAnd && Pred == ICmpInst::Predicate::ICMP_EQ &&
58        match(Op1, m_Not(m_Value(NotOp1))) && matchMulOverflowCheck(NotOp1));
59 
60   if (!Matched)
61     return false;
62 
63   Y = &II->getArgOperandUse(!XIdx);
64   return true;
65 }
66 
67 bool llvm::isCheckForZeroAndMulWithOverflow(Value *Op0, Value *Op1,
68                                             bool IsAnd) {
69   Use *Y;
70   return isCheckForZeroAndMulWithOverflow(Op0, Op1, IsAnd, Y);
71 }
72