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[analyzer] Model overflow builtins (#102602)
Add basic support for `builtin_*_overflow` primitives. These helps a lot for checking custom calloc-like functions with inlinable body. Without such support code like ```c #include <stddef.h> #include <stdlib.h> static void *myMalloc(size_t a1, size_t a2) { size_t res; if (__builtin_mul_overflow(a1, a2, &res)) return NULL; return malloc(res); } void test(void) { char *ptr = myMalloc(10, 1); ptr[20] = 10; } ```` does not trigger any warnings.
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‎clang/docs/ReleaseNotes.rst‎

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@@ -628,6 +628,8 @@ Static Analyzer
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New features
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^^^^^^^^^^^^
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- Now CSA models `__builtin_*_overflow` functions. (#GH102602)
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- MallocChecker now checks for ``ownership_returns(class, idx)`` and ``ownership_takes(class, idx)``
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attributes with class names different from "malloc". Clang static analyzer now reports an error
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if class of allocation and deallocation function mismatches.

‎clang/lib/StaticAnalyzer/Checkers/BuiltinFunctionChecker.cpp‎

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@@ -16,21 +16,93 @@
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#include "clang/Basic/Builtins.h"
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#include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
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#include "clang/StaticAnalyzer/Checkers/Taint.h"
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#include "clang/StaticAnalyzer/Core/Checker.h"
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#include "clang/StaticAnalyzer/Core/CheckerManager.h"
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#include "clang/StaticAnalyzer/Core/PathSensitive/CallDescription.h"
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#include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h"
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#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
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#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerHelpers.h"
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#include "clang/StaticAnalyzer/Core/PathSensitive/DynamicExtent.h"
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#include "clang/StaticAnalyzer/Core/PathSensitive/SVals.h"
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using namespace clang;
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using namespace ento;
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using namespace taint;
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namespace {
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QualType getSufficientTypeForOverflowOp(CheckerContext &C, const QualType &T) {
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// Calling a builtin with a non-integer type result produces compiler error.
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assert(T->isIntegerType());
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ASTContext &ACtx = C.getASTContext();
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unsigned BitWidth = ACtx.getIntWidth(T);
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return ACtx.getIntTypeForBitwidth(BitWidth * 2, T->isSignedIntegerType());
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}
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QualType getOverflowBuiltinResultType(const CallEvent &Call) {
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// Calling a builtin with an incorrect argument count produces compiler error.
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assert(Call.getNumArgs() == 3);
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return Call.getArgExpr(2)->getType()->getPointeeType();
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}
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QualType getOverflowBuiltinResultType(const CallEvent &Call, CheckerContext &C,
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unsigned BI) {
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// Calling a builtin with an incorrect argument count produces compiler error.
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assert(Call.getNumArgs() == 3);
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ASTContext &ACtx = C.getASTContext();
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switch (BI) {
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case Builtin::BI__builtin_smul_overflow:
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case Builtin::BI__builtin_ssub_overflow:
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case Builtin::BI__builtin_sadd_overflow:
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return ACtx.IntTy;
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case Builtin::BI__builtin_smull_overflow:
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case Builtin::BI__builtin_ssubl_overflow:
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case Builtin::BI__builtin_saddl_overflow:
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return ACtx.LongTy;
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case Builtin::BI__builtin_smulll_overflow:
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case Builtin::BI__builtin_ssubll_overflow:
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case Builtin::BI__builtin_saddll_overflow:
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return ACtx.LongLongTy;
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case Builtin::BI__builtin_umul_overflow:
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case Builtin::BI__builtin_usub_overflow:
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case Builtin::BI__builtin_uadd_overflow:
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return ACtx.UnsignedIntTy;
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case Builtin::BI__builtin_umull_overflow:
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case Builtin::BI__builtin_usubl_overflow:
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case Builtin::BI__builtin_uaddl_overflow:
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return ACtx.UnsignedLongTy;
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case Builtin::BI__builtin_umulll_overflow:
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case Builtin::BI__builtin_usubll_overflow:
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case Builtin::BI__builtin_uaddll_overflow:
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return ACtx.UnsignedLongLongTy;
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case Builtin::BI__builtin_mul_overflow:
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case Builtin::BI__builtin_sub_overflow:
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case Builtin::BI__builtin_add_overflow:
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return getOverflowBuiltinResultType(Call);
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default:
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assert(false && "Unknown overflow builtin");
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return ACtx.IntTy;
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}
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}
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class BuiltinFunctionChecker : public Checker<eval::Call> {
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public:
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bool evalCall(const CallEvent &Call, CheckerContext &C) const;
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void handleOverflowBuiltin(const CallEvent &Call, CheckerContext &C,
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BinaryOperator::Opcode Op,
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QualType ResultType) const;
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const NoteTag *createBuiltinNoOverflowNoteTag(CheckerContext &C,
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bool BothFeasible, SVal Arg1,
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SVal Arg2, SVal Result) const;
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const NoteTag *createBuiltinOverflowNoteTag(CheckerContext &C) const;
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std::pair<bool, bool> checkOverflow(CheckerContext &C, SVal RetVal,
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QualType Res) const;
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private:
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// From: clang/include/clang/Basic/Builtins.def
@@ -50,6 +122,102 @@ class BuiltinFunctionChecker : public Checker<eval::Call> {
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} // namespace
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const NoteTag *BuiltinFunctionChecker::createBuiltinNoOverflowNoteTag(
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CheckerContext &C, bool BothFeasible, SVal Arg1, SVal Arg2,
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SVal Result) const {
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return C.getNoteTag([Result, Arg1, Arg2, BothFeasible](
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PathSensitiveBugReport &BR, llvm::raw_ostream &OS) {
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if (!BR.isInteresting(Result))
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return;
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// Propagate interestingness to input argumets if result is interesting.
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BR.markInteresting(Arg1);
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BR.markInteresting(Arg2);
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if (BothFeasible)
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OS << "Assuming no overflow";
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});
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}
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const NoteTag *
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BuiltinFunctionChecker::createBuiltinOverflowNoteTag(CheckerContext &C) const {
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return C.getNoteTag([](PathSensitiveBugReport &BR,
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llvm::raw_ostream &OS) { OS << "Assuming overflow"; },
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/*isPrunable=*/true);
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}
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std::pair<bool, bool>
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BuiltinFunctionChecker::checkOverflow(CheckerContext &C, SVal RetVal,
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QualType Res) const {
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// Calling a builtin with a non-integer type result produces compiler error.
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assert(Res->isIntegerType());
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unsigned BitWidth = C.getASTContext().getIntWidth(Res);
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bool IsUnsigned = Res->isUnsignedIntegerType();
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auto MinValType = llvm::APSInt::getMinValue(BitWidth, IsUnsigned);
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auto MaxValType = llvm::APSInt::getMaxValue(BitWidth, IsUnsigned);
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nonloc::ConcreteInt MinVal{MinValType};
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nonloc::ConcreteInt MaxVal{MaxValType};
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SValBuilder &SVB = C.getSValBuilder();
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ProgramStateRef State = C.getState();
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SVal IsLeMax = SVB.evalBinOp(State, BO_LE, RetVal, MaxVal, Res);
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SVal IsGeMin = SVB.evalBinOp(State, BO_GE, RetVal, MinVal, Res);
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auto [MayNotOverflow, MayOverflow] =
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State->assume(IsLeMax.castAs<DefinedOrUnknownSVal>());
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auto [MayNotUnderflow, MayUnderflow] =
171+
State->assume(IsGeMin.castAs<DefinedOrUnknownSVal>());
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173+
return {MayOverflow || MayUnderflow, MayNotOverflow && MayNotUnderflow};
174+
}
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void BuiltinFunctionChecker::handleOverflowBuiltin(const CallEvent &Call,
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CheckerContext &C,
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BinaryOperator::Opcode Op,
179+
QualType ResultType) const {
180+
// Calling a builtin with an incorrect argument count produces compiler error.
181+
assert(Call.getNumArgs() == 3);
182+
183+
ProgramStateRef State = C.getState();
184+
SValBuilder &SVB = C.getSValBuilder();
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const Expr *CE = Call.getOriginExpr();
186+
187+
SVal Arg1 = Call.getArgSVal(0);
188+
SVal Arg2 = Call.getArgSVal(1);
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190+
SVal RetValMax = SVB.evalBinOp(State, Op, Arg1, Arg2,
191+
getSufficientTypeForOverflowOp(C, ResultType));
192+
SVal RetVal = SVB.evalBinOp(State, Op, Arg1, Arg2, ResultType);
193+
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auto [Overflow, NotOverflow] = checkOverflow(C, RetValMax, ResultType);
195+
if (NotOverflow) {
196+
ProgramStateRef StateNoOverflow =
197+
State->BindExpr(CE, C.getLocationContext(), SVB.makeTruthVal(false));
198+
199+
if (auto L = Call.getArgSVal(2).getAs<Loc>()) {
200+
StateNoOverflow =
201+
StateNoOverflow->bindLoc(*L, RetVal, C.getLocationContext());
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// Propagate taint if any of the argumets were tainted
204+
if (isTainted(State, Arg1) || isTainted(State, Arg2))
205+
StateNoOverflow = addTaint(StateNoOverflow, *L);
206+
}
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C.addTransition(
209+
StateNoOverflow,
210+
createBuiltinNoOverflowNoteTag(
211+
C, /*BothFeasible=*/NotOverflow && Overflow, Arg1, Arg2, RetVal));
212+
}
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if (Overflow) {
215+
C.addTransition(
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State->BindExpr(CE, C.getLocationContext(), SVB.makeTruthVal(true)),
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createBuiltinOverflowNoteTag(C));
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}
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}
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53221
bool BuiltinFunctionChecker::isBuiltinLikeFunction(
54222
const CallEvent &Call) const {
55223
const auto *FD = llvm::dyn_cast_or_null<FunctionDecl>(Call.getDecl());
@@ -82,10 +250,41 @@ bool BuiltinFunctionChecker::evalCall(const CallEvent &Call,
82250
return true;
83251
}
84252

85-
switch (FD->getBuiltinID()) {
253+
unsigned BI = FD->getBuiltinID();
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switch (BI) {
86256
default:
87257
return false;
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case Builtin::BI__builtin_mul_overflow:
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case Builtin::BI__builtin_smul_overflow:
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case Builtin::BI__builtin_smull_overflow:
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case Builtin::BI__builtin_smulll_overflow:
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case Builtin::BI__builtin_umul_overflow:
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case Builtin::BI__builtin_umull_overflow:
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case Builtin::BI__builtin_umulll_overflow:
265+
handleOverflowBuiltin(Call, C, BO_Mul,
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getOverflowBuiltinResultType(Call, C, BI));
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return true;
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case Builtin::BI__builtin_sub_overflow:
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case Builtin::BI__builtin_ssub_overflow:
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case Builtin::BI__builtin_ssubl_overflow:
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case Builtin::BI__builtin_ssubll_overflow:
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case Builtin::BI__builtin_usub_overflow:
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case Builtin::BI__builtin_usubl_overflow:
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case Builtin::BI__builtin_usubll_overflow:
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handleOverflowBuiltin(Call, C, BO_Sub,
276+
getOverflowBuiltinResultType(Call, C, BI));
277+
return true;
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case Builtin::BI__builtin_add_overflow:
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case Builtin::BI__builtin_sadd_overflow:
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case Builtin::BI__builtin_saddl_overflow:
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case Builtin::BI__builtin_saddll_overflow:
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case Builtin::BI__builtin_uadd_overflow:
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case Builtin::BI__builtin_uaddl_overflow:
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case Builtin::BI__builtin_uaddll_overflow:
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handleOverflowBuiltin(Call, C, BO_Add,
286+
getOverflowBuiltinResultType(Call, C, BI));
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return true;
89288
case Builtin::BI__builtin_assume:
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case Builtin::BI__assume: {
91290
assert (Call.getNumArgs() > 0);

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