r338941 - [constexpr] Support for constant evaluation of __builtin_memcpy and

Shoaib Meenai via cfe-commits cfe-commits at lists.llvm.org
Wed Nov 21 15:32:22 PST 2018


If it's not too late, could we have this as part of 7.0.1? (You'll also
need to cherry-pick the initial reversion in r338602.) 7.0 hits assertion
failures for pretty basic memcpy cases on windows-msvc targets, and this
patch fixes that.

% cat /tmp/reduced.c
void *memcpy(void *, const void *, __SIZE_TYPE__);
void f(int i) {
  struct { int i } s;
  memcpy((char *)&s.i, &i, sizeof(i));
}

% clang -cc1 -triple x86_64-windows-msvc -emit-llvm -fms-compatibility -o
/dev/null /tmp/reduced.c
llvm::SmallVectorTemplateCommon::const_reference
llvm::SmallVectorTemplateCommon<clang::APValue::LValuePathEntry,
void>::back() const [T = clang::APValue::LValuePathEntry]: Assertion
`!empty()' failed.

On Fri, Aug 3, 2018 at 5:57 PM Richard Smith via cfe-commits <
cfe-commits at lists.llvm.org> wrote:

> Author: rsmith
> Date: Fri Aug  3 17:57:17 2018
> New Revision: 338941
>
> URL: http://llvm.org/viewvc/llvm-project?rev=338941&view=rev
> Log:
> [constexpr] Support for constant evaluation of __builtin_memcpy and
> __builtin_memmove (in non-type-punning cases).
>
> This is intended to permit libc++ to make std::copy etc constexpr
> without sacrificing the optimization that uses memcpy on
> trivially-copyable types.
>
> __builtin_strcpy and __builtin_wcscpy are not handled by this change.
> They'd be straightforward to add, but we haven't encountered a need for
> them just yet.
>
> This reinstates r338455, reverted in r338602, with a fix to avoid trying
> to constant-evaluate a memcpy call if either pointer operand has an
> invalid designator.
>
> Modified:
>     cfe/trunk/include/clang/Basic/Builtins.def
>     cfe/trunk/include/clang/Basic/DiagnosticASTKinds.td
>     cfe/trunk/lib/AST/ExprConstant.cpp
>     cfe/trunk/test/CodeGen/builtin-memfns.c
>     cfe/trunk/test/SemaCXX/constexpr-string.cpp
>
> Modified: cfe/trunk/include/clang/Basic/Builtins.def
> URL:
> http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/Builtins.def?rev=338941&r1=338940&r2=338941&view=diff
>
> ==============================================================================
> --- cfe/trunk/include/clang/Basic/Builtins.def (original)
> +++ cfe/trunk/include/clang/Basic/Builtins.def Fri Aug  3 17:57:17 2018
> @@ -471,6 +471,8 @@ BUILTIN(__builtin_wcslen, "zwC*", "nF")
>  BUILTIN(__builtin_wcsncmp, "iwC*wC*z", "nF")
>  BUILTIN(__builtin_wmemchr, "w*wC*wz", "nF")
>  BUILTIN(__builtin_wmemcmp, "iwC*wC*z", "nF")
> +BUILTIN(__builtin_wmemcpy, "w*w*wC*z", "nF")
> +BUILTIN(__builtin_wmemmove, "w*w*wC*z", "nF")
>  BUILTIN(__builtin_return_address, "v*IUi", "n")
>  BUILTIN(__builtin_extract_return_addr, "v*v*", "n")
>  BUILTIN(__builtin_frame_address, "v*IUi", "n")
> @@ -908,6 +910,8 @@ LIBBUILTIN(wcslen,  "zwC*",     "f", "wc
>  LIBBUILTIN(wcsncmp, "iwC*wC*z", "f", "wchar.h", ALL_LANGUAGES)
>  LIBBUILTIN(wmemchr, "w*wC*wz",  "f", "wchar.h", ALL_LANGUAGES)
>  LIBBUILTIN(wmemcmp, "iwC*wC*z", "f", "wchar.h", ALL_LANGUAGES)
> +LIBBUILTIN(wmemcpy, "w*w*wC*z", "f", "wchar.h", ALL_LANGUAGES)
> +LIBBUILTIN(wmemmove,"w*w*wC*z", "f", "wchar.h", ALL_LANGUAGES)
>
>  // C99
>  // In some systems setjmp is a macro that expands to _setjmp. We undefine
>
> Modified: cfe/trunk/include/clang/Basic/DiagnosticASTKinds.td
> URL:
> http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/DiagnosticASTKinds.td?rev=338941&r1=338940&r2=338941&view=diff
>
> ==============================================================================
> --- cfe/trunk/include/clang/Basic/DiagnosticASTKinds.td (original)
> +++ cfe/trunk/include/clang/Basic/DiagnosticASTKinds.td Fri Aug  3
> 17:57:17 2018
> @@ -163,6 +163,20 @@ def note_constexpr_unsupported_unsized_a
>  def note_constexpr_unsized_array_indexed : Note<
>    "indexing of array without known bound is not allowed "
>    "in a constant expression">;
> +def note_constexpr_memcpy_type_pun : Note<
> +  "cannot constant evaluate '%select{memcpy|memmove}0' from object of "
> +  "type %1 to object of type %2">;
> +def note_constexpr_memcpy_nontrivial : Note<
> +  "cannot constant evaluate '%select{memcpy|memmove}0' between objects of
> "
> +  "non-trivially-copyable type %1">;
> +def note_constexpr_memcpy_overlap : Note<
> +  "'%select{memcpy|wmemcpy}0' between overlapping memory regions">;
> +def note_constexpr_memcpy_unsupported : Note<
> +  "'%select{%select{memcpy|wmemcpy}1|%select{memmove|wmemmove}1}0' "
> +  "not supported: %select{"
> +  "size to copy (%4) is not a multiple of size of element type %3 (%5)|"
> +  "source is not a contiguous array of at least %4 elements of type %3|"
> +  "destination is not a contiguous array of at least %4 elements of type
> %3}2">;
>
>  def warn_integer_constant_overflow : Warning<
>    "overflow in expression; result is %0 with type %1">,
>
> Modified: cfe/trunk/lib/AST/ExprConstant.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/AST/ExprConstant.cpp?rev=338941&r1=338940&r2=338941&view=diff
>
> ==============================================================================
> --- cfe/trunk/lib/AST/ExprConstant.cpp (original)
> +++ cfe/trunk/lib/AST/ExprConstant.cpp Fri Aug  3 17:57:17 2018
> @@ -319,6 +319,25 @@ namespace {
>        return false;
>      }
>
> +    /// Get the range of valid index adjustments in the form
> +    ///   {maximum value that can be subtracted from this pointer,
> +    ///    maximum value that can be added to this pointer}
> +    std::pair<uint64_t, uint64_t> validIndexAdjustments() {
> +      if (Invalid || isMostDerivedAnUnsizedArray())
> +        return {0, 0};
> +
> +      // [expr.add]p4: For the purposes of these operators, a pointer to a
> +      // nonarray object behaves the same as a pointer to the first
> element of
> +      // an array of length one with the type of the object as its
> element type.
> +      bool IsArray = MostDerivedPathLength == Entries.size() &&
> +                     MostDerivedIsArrayElement;
> +      uint64_t ArrayIndex =
> +          IsArray ? Entries.back().ArrayIndex : (uint64_t)IsOnePastTheEnd;
> +      uint64_t ArraySize =
> +          IsArray ? getMostDerivedArraySize() : (uint64_t)1;
> +      return {ArrayIndex, ArraySize - ArrayIndex};
> +    }
> +
>      /// Check that this refers to a valid subobject.
>      bool isValidSubobject() const {
>        if (Invalid)
> @@ -329,6 +348,14 @@ namespace {
>      /// relevant diagnostic and set the designator as invalid.
>      bool checkSubobject(EvalInfo &Info, const Expr *E, CheckSubobjectKind
> CSK);
>
> +    /// Get the type of the designated object.
> +    QualType getType(ASTContext &Ctx) const {
> +      assert(!Invalid && "invalid designator has no subobject type");
> +      return MostDerivedPathLength == Entries.size()
> +                 ? MostDerivedType
> +                 : Ctx.getRecordType(getAsBaseClass(Entries.back()));
> +    }
> +
>      /// Update this designator to refer to the first element within this
> array.
>      void addArrayUnchecked(const ConstantArrayType *CAT) {
>        PathEntry Entry;
> @@ -1706,6 +1733,54 @@ static bool IsGlobalLValue(APValue::LVal
>    }
>  }
>
> +static const ValueDecl *GetLValueBaseDecl(const LValue &LVal) {
> +  return LVal.Base.dyn_cast<const ValueDecl*>();
> +}
> +
> +static bool IsLiteralLValue(const LValue &Value) {
> +  if (Value.getLValueCallIndex())
> +    return false;
> +  const Expr *E = Value.Base.dyn_cast<const Expr*>();
> +  return E && !isa<MaterializeTemporaryExpr>(E);
> +}
> +
> +static bool IsWeakLValue(const LValue &Value) {
> +  const ValueDecl *Decl = GetLValueBaseDecl(Value);
> +  return Decl && Decl->isWeak();
> +}
> +
> +static bool isZeroSized(const LValue &Value) {
> +  const ValueDecl *Decl = GetLValueBaseDecl(Value);
> +  if (Decl && isa<VarDecl>(Decl)) {
> +    QualType Ty = Decl->getType();
> +    if (Ty->isArrayType())
> +      return Ty->isIncompleteType() ||
> +             Decl->getASTContext().getTypeSize(Ty) == 0;
> +  }
> +  return false;
> +}
> +
> +static bool HasSameBase(const LValue &A, const LValue &B) {
> +  if (!A.getLValueBase())
> +    return !B.getLValueBase();
> +  if (!B.getLValueBase())
> +    return false;
> +
> +  if (A.getLValueBase().getOpaqueValue() !=
> +      B.getLValueBase().getOpaqueValue()) {
> +    const Decl *ADecl = GetLValueBaseDecl(A);
> +    if (!ADecl)
> +      return false;
> +    const Decl *BDecl = GetLValueBaseDecl(B);
> +    if (!BDecl || ADecl->getCanonicalDecl() != BDecl->getCanonicalDecl())
> +      return false;
> +  }
> +
> +  return IsGlobalLValue(A.getLValueBase()) ||
> +         (A.getLValueCallIndex() == B.getLValueCallIndex() &&
> +          A.getLValueVersion() == B.getLValueVersion());
> +}
> +
>  static void NoteLValueLocation(EvalInfo &Info, APValue::LValueBase Base) {
>    assert(Base && "no location for a null lvalue");
>    const ValueDecl *VD = Base.dyn_cast<const ValueDecl*>();
> @@ -1917,33 +1992,6 @@ CheckConstantExpression(EvalInfo &Info,
>    return true;
>  }
>
> -static const ValueDecl *GetLValueBaseDecl(const LValue &LVal) {
> -  return LVal.Base.dyn_cast<const ValueDecl*>();
> -}
> -
> -static bool IsLiteralLValue(const LValue &Value) {
> -  if (Value.getLValueCallIndex())
> -    return false;
> -  const Expr *E = Value.Base.dyn_cast<const Expr*>();
> -  return E && !isa<MaterializeTemporaryExpr>(E);
> -}
> -
> -static bool IsWeakLValue(const LValue &Value) {
> -  const ValueDecl *Decl = GetLValueBaseDecl(Value);
> -  return Decl && Decl->isWeak();
> -}
> -
> -static bool isZeroSized(const LValue &Value) {
> -  const ValueDecl *Decl = GetLValueBaseDecl(Value);
> -  if (Decl && isa<VarDecl>(Decl)) {
> -    QualType Ty = Decl->getType();
> -    if (Ty->isArrayType())
> -      return Ty->isIncompleteType() ||
> -             Decl->getASTContext().getTypeSize(Ty) == 0;
> -  }
> -  return false;
> -}
> -
>  static bool EvalPointerValueAsBool(const APValue &Value, bool &Result) {
>    // A null base expression indicates a null pointer.  These are always
>    // evaluatable, and they are false unless the offset is zero.
> @@ -6117,6 +6165,130 @@ bool PointerExprEvaluator::VisitBuiltinC
>      return ZeroInitialization(E);
>    }
>
> +  case Builtin::BImemcpy:
> +  case Builtin::BImemmove:
> +  case Builtin::BIwmemcpy:
> +  case Builtin::BIwmemmove:
> +    if (Info.getLangOpts().CPlusPlus11)
> +      Info.CCEDiag(E, diag::note_constexpr_invalid_function)
> +        << /*isConstexpr*/0 << /*isConstructor*/0
> +        << (std::string("'") + Info.Ctx.BuiltinInfo.getName(BuiltinOp) +
> "'");
> +    else
> +      Info.CCEDiag(E, diag::note_invalid_subexpr_in_const_expr);
> +    LLVM_FALLTHROUGH;
> +  case Builtin::BI__builtin_memcpy:
> +  case Builtin::BI__builtin_memmove:
> +  case Builtin::BI__builtin_wmemcpy:
> +  case Builtin::BI__builtin_wmemmove: {
> +    bool WChar = BuiltinOp == Builtin::BIwmemcpy ||
> +                 BuiltinOp == Builtin::BIwmemmove ||
> +                 BuiltinOp == Builtin::BI__builtin_wmemcpy ||
> +                 BuiltinOp == Builtin::BI__builtin_wmemmove;
> +    bool Move = BuiltinOp == Builtin::BImemmove ||
> +                BuiltinOp == Builtin::BIwmemmove ||
> +                BuiltinOp == Builtin::BI__builtin_memmove ||
> +                BuiltinOp == Builtin::BI__builtin_wmemmove;
> +
> +    // The result of mem* is the first argument.
> +    if (!Visit(E->getArg(0)) || Result.Designator.Invalid)
> +      return false;
> +    LValue Dest = Result;
> +
> +    LValue Src;
> +    if (!EvaluatePointer(E->getArg(1), Src, Info) ||
> Src.Designator.Invalid)
> +      return false;
> +
> +    APSInt N;
> +    if (!EvaluateInteger(E->getArg(2), N, Info))
> +      return false;
> +    assert(!N.isSigned() && "memcpy and friends take an unsigned size");
> +
> +    // If the size is zero, we treat this as always being a valid no-op.
> +    // (Even if one of the src and dest pointers is null.)
> +    if (!N)
> +      return true;
> +
> +    // We require that Src and Dest are both pointers to arrays of
> +    // trivially-copyable type. (For the wide version, the designator
> will be
> +    // invalid if the designated object is not a wchar_t.)
> +    QualType T = Dest.Designator.getType(Info.Ctx);
> +    QualType SrcT = Src.Designator.getType(Info.Ctx);
> +    if (!Info.Ctx.hasSameUnqualifiedType(T, SrcT)) {
> +      Info.FFDiag(E, diag::note_constexpr_memcpy_type_pun) << Move <<
> SrcT << T;
> +      return false;
> +    }
> +    if (!T.isTriviallyCopyableType(Info.Ctx)) {
> +      Info.FFDiag(E, diag::note_constexpr_memcpy_nontrivial) << Move << T;
> +      return false;
> +    }
> +
> +    // Figure out how many T's we're copying.
> +    uint64_t TSize = Info.Ctx.getTypeSizeInChars(T).getQuantity();
> +    if (!WChar) {
> +      uint64_t Remainder;
> +      llvm::APInt OrigN = N;
> +      llvm::APInt::udivrem(OrigN, TSize, N, Remainder);
> +      if (Remainder) {
> +        Info.FFDiag(E, diag::note_constexpr_memcpy_unsupported)
> +            << Move << WChar << 0 << T << OrigN.toString(10,
> /*Signed*/false)
> +            << (unsigned)TSize;
> +        return false;
> +      }
> +    }
> +
> +    // Check that the copying will remain within the arrays, just so that
> we
> +    // can give a more meaningful diagnostic. This implicitly also checks
> that
> +    // N fits into 64 bits.
> +    uint64_t RemainingSrcSize =
> Src.Designator.validIndexAdjustments().second;
> +    uint64_t RemainingDestSize =
> Dest.Designator.validIndexAdjustments().second;
> +    if (N.ugt(RemainingSrcSize) || N.ugt(RemainingDestSize)) {
> +      Info.FFDiag(E, diag::note_constexpr_memcpy_unsupported)
> +          << Move << WChar << (N.ugt(RemainingSrcSize) ? 1 : 2) << T
> +          << N.toString(10, /*Signed*/false);
> +      return false;
> +    }
> +    uint64_t NElems = N.getZExtValue();
> +    uint64_t NBytes = NElems * TSize;
> +
> +    // Check for overlap.
> +    int Direction = 1;
> +    if (HasSameBase(Src, Dest)) {
> +      uint64_t SrcOffset = Src.getLValueOffset().getQuantity();
> +      uint64_t DestOffset = Dest.getLValueOffset().getQuantity();
> +      if (DestOffset >= SrcOffset && DestOffset - SrcOffset < NBytes) {
> +        // Dest is inside the source region.
> +        if (!Move) {
> +          Info.FFDiag(E, diag::note_constexpr_memcpy_overlap) << WChar;
> +          return false;
> +        }
> +        // For memmove and friends, copy backwards.
> +        if (!HandleLValueArrayAdjustment(Info, E, Src, T, NElems - 1) ||
> +            !HandleLValueArrayAdjustment(Info, E, Dest, T, NElems - 1))
> +          return false;
> +        Direction = -1;
> +      } else if (!Move && SrcOffset >= DestOffset &&
> +                 SrcOffset - DestOffset < NBytes) {
> +        // Src is inside the destination region for memcpy: invalid.
> +        Info.FFDiag(E, diag::note_constexpr_memcpy_overlap) << WChar;
> +        return false;
> +      }
> +    }
> +
> +    while (true) {
> +      APValue Val;
> +      if (!handleLValueToRValueConversion(Info, E, T, Src, Val) ||
> +          !handleAssignment(Info, E, Dest, T, Val))
> +        return false;
> +      // Do not iterate past the last element; if we're copying
> backwards, that
> +      // might take us off the start of the array.
> +      if (--NElems == 0)
> +        return true;
> +      if (!HandleLValueArrayAdjustment(Info, E, Src, T, Direction) ||
> +          !HandleLValueArrayAdjustment(Info, E, Dest, T, Direction))
> +        return false;
> +    }
> +  }
> +
>    default:
>      return visitNonBuiltinCallExpr(E);
>    }
> @@ -8357,27 +8529,6 @@ bool IntExprEvaluator::VisitBuiltinCallE
>    }
>  }
>
> -static bool HasSameBase(const LValue &A, const LValue &B) {
> -  if (!A.getLValueBase())
> -    return !B.getLValueBase();
> -  if (!B.getLValueBase())
> -    return false;
> -
> -  if (A.getLValueBase().getOpaqueValue() !=
> -      B.getLValueBase().getOpaqueValue()) {
> -    const Decl *ADecl = GetLValueBaseDecl(A);
> -    if (!ADecl)
> -      return false;
> -    const Decl *BDecl = GetLValueBaseDecl(B);
> -    if (!BDecl || ADecl->getCanonicalDecl() != BDecl->getCanonicalDecl())
> -      return false;
> -  }
> -
> -  return IsGlobalLValue(A.getLValueBase()) ||
> -         (A.getLValueCallIndex() == B.getLValueCallIndex() &&
> -          A.getLValueVersion() == B.getLValueVersion());
> -}
> -
>  /// Determine whether this is a pointer past the end of the complete
>  /// object referred to by the lvalue.
>  static bool isOnePastTheEndOfCompleteObject(const ASTContext &Ctx,
>
> Modified: cfe/trunk/test/CodeGen/builtin-memfns.c
> URL:
> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGen/builtin-memfns.c?rev=338941&r1=338940&r2=338941&view=diff
>
> ==============================================================================
> --- cfe/trunk/test/CodeGen/builtin-memfns.c (original)
> +++ cfe/trunk/test/CodeGen/builtin-memfns.c Fri Aug  3 17:57:17 2018
> @@ -1,5 +1,10 @@
>  // RUN: %clang_cc1 -triple i386-pc-linux-gnu -emit-llvm < %s| FileCheck %s
>
> +typedef __WCHAR_TYPE__ wchar_t;
> +typedef __SIZE_TYPE__ size_t;
> +
> +void *memcpy(void *, void const *, size_t);
> +
>  // CHECK: @test1
>  // CHECK: call void @llvm.memset.p0i8.i32
>  // CHECK: call void @llvm.memset.p0i8.i32
> @@ -83,3 +88,26 @@ void test9() {
>    // CHECK: call void @llvm.memcpy{{.*}} align 16 {{.*}} align 16 {{.*}}
> 16, i1 false)
>    __builtin_memcpy(x, y, sizeof(y));
>  }
> +
> +wchar_t dest;
> +wchar_t src;
> +
> +// CHECK-LABEL: @test10
> +// FIXME: Consider lowering these to llvm.memcpy / llvm.memmove.
> +void test10() {
> +  // CHECK: call i32* @wmemcpy(i32* @dest, i32* @src, i32 4)
> +  __builtin_wmemcpy(&dest, &src, 4);
> +
> +  // CHECK: call i32* @wmemmove(i32* @dest, i32* @src, i32 4)
> +  __builtin_wmemmove(&dest, &src, 4);
> +}
> +
> +// CHECK-LABEL: @test11
> +void test11() {
> +  typedef struct { int a; } b;
> +  int d;
> +  b e;
> +  // CHECK: call void @llvm.memcpy{{.*}}(
> +  memcpy(&d, (char *)&e.a, sizeof(e));
> +}
> +
>
> Modified: cfe/trunk/test/SemaCXX/constexpr-string.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/constexpr-string.cpp?rev=338941&r1=338940&r2=338941&view=diff
>
> ==============================================================================
> --- cfe/trunk/test/SemaCXX/constexpr-string.cpp (original)
> +++ cfe/trunk/test/SemaCXX/constexpr-string.cpp Fri Aug  3 17:57:17 2018
> @@ -1,6 +1,6 @@
> -// RUN: %clang_cc1 %s -std=c++1z -fsyntax-only -verify -pedantic
> -// RUN: %clang_cc1 %s -std=c++1z -fsyntax-only -verify -pedantic
> -fno-signed-char
> -// RUN: %clang_cc1 %s -std=c++1z -fsyntax-only -verify -pedantic
> -fno-wchar -Dwchar_t=__WCHAR_TYPE__
> +// RUN: %clang_cc1 %s -triple x86_64-linux-gnu -std=c++1z -fsyntax-only
> -verify -pedantic
> +// RUN: %clang_cc1 %s -triple x86_64-linux-gnu -std=c++1z -fsyntax-only
> -verify -pedantic -fno-signed-char
> +// RUN: %clang_cc1 %s -triple x86_64-linux-gnu -std=c++1z -fsyntax-only
> -verify -pedantic -fno-wchar -Dwchar_t=__WCHAR_TYPE__
>
>  # 6 "/usr/include/string.h" 1 3 4
>  extern "C" {
> @@ -14,10 +14,13 @@ extern "C" {
>
>    extern char *strchr(const char *s, int c);
>    extern void *memchr(const void *s, int c, size_t n);
> +
> +  extern void *memcpy(void *d, const void *s, size_t n);
> +  extern void *memmove(void *d, const void *s, size_t n);
>  }
> -# 19 "SemaCXX/constexpr-string.cpp" 2
> +# 22 "SemaCXX/constexpr-string.cpp" 2
>
> -# 21 "/usr/include/wchar.h" 1 3 4
> +# 24 "/usr/include/wchar.h" 1 3 4
>  extern "C" {
>    extern size_t wcslen(const wchar_t *p);
>
> @@ -27,9 +30,12 @@ extern "C" {
>
>    extern wchar_t *wcschr(const wchar_t *s, wchar_t c);
>    extern wchar_t *wmemchr(const wchar_t *s, wchar_t c, size_t n);
> +
> +  extern wchar_t *wmemcpy(wchar_t *d, const wchar_t *s, size_t n);
> +  extern wchar_t *wmemmove(wchar_t *d, const wchar_t *s, size_t n);
>  }
>
> -# 33 "SemaCXX/constexpr-string.cpp" 2
> +# 39 "SemaCXX/constexpr-string.cpp" 2
>  namespace Strlen {
>    constexpr int n = __builtin_strlen("hello"); // ok
>    static_assert(n == 5);
> @@ -235,3 +241,133 @@ namespace WcschrEtc {
>    constexpr bool a = !wcschr(L"hello", L'h'); // expected-error
> {{constant expression}} expected-note {{non-constexpr function 'wcschr'
> cannot be used in a constant expression}}
>    constexpr bool b = !wmemchr(L"hello", L'h', 3); // expected-error
> {{constant expression}} expected-note {{non-constexpr function 'wmemchr'
> cannot be used in a constant expression}}
>  }
> +
> +namespace MemcpyEtc {
> +  template<typename T>
> +  constexpr T result(T (&arr)[4]) {
> +    return arr[0] * 1000 + arr[1] * 100 + arr[2] * 10 + arr[3];
> +  }
> +
> +  constexpr int test_memcpy(int a, int b, int n) {
> +    int arr[4] = {1, 2, 3, 4};
> +    __builtin_memcpy(arr + a, arr + b, n);
> +    // expected-note at -1 2{{overlapping memory regions}}
> +    // expected-note at -2 {{size to copy (1) is not a multiple of size of
> element type 'int'}}
> +    // expected-note at -3 {{source is not a contiguous array of at least 2
> elements of type 'int'}}
> +    // expected-note at -4 {{destination is not a contiguous array of at
> least 3 elements of type 'int'}}
> +    return result(arr);
> +  }
> +  constexpr int test_memmove(int a, int b, int n) {
> +    int arr[4] = {1, 2, 3, 4};
> +    __builtin_memmove(arr + a, arr + b, n);
> +    // expected-note at -1 {{size to copy (1) is not a multiple of size of
> element type 'int'}}
> +    // expected-note at -2 {{source is not a contiguous array of at least 2
> elements of type 'int'}}
> +    // expected-note at -3 {{destination is not a contiguous array of at
> least 3 elements of type 'int'}}
> +    return result(arr);
> +  }
> +  constexpr int test_wmemcpy(int a, int b, int n) {
> +    wchar_t arr[4] = {1, 2, 3, 4};
> +    __builtin_wmemcpy(arr + a, arr + b, n);
> +    // expected-note at -1 2{{overlapping memory regions}}
> +    // expected-note-re at -2 {{source is not a contiguous array of at
> least 2 elements of type '{{wchar_t|int}}'}}
> +    // expected-note-re at -3 {{destination is not a contiguous array of at
> least 3 elements of type '{{wchar_t|int}}'}}
> +    return result(arr);
> +  }
> +  constexpr int test_wmemmove(int a, int b, int n) {
> +    wchar_t arr[4] = {1, 2, 3, 4};
> +    __builtin_wmemmove(arr + a, arr + b, n);
> +    // expected-note-re at -1 {{source is not a contiguous array of at
> least 2 elements of type '{{wchar_t|int}}'}}
> +    // expected-note-re at -2 {{destination is not a contiguous array of at
> least 3 elements of type '{{wchar_t|int}}'}}
> +    return result(arr);
> +  }
> +
> +  static_assert(test_memcpy(1, 2, 4) == 1334);
> +  static_assert(test_memcpy(2, 1, 4) == 1224);
> +  static_assert(test_memcpy(0, 1, 8) == 2334); // expected-error
> {{constant}} expected-note {{in call}}
> +  static_assert(test_memcpy(1, 0, 8) == 1124); // expected-error
> {{constant}} expected-note {{in call}}
> +  static_assert(test_memcpy(1, 2, 1) == 1334); // expected-error
> {{constant}} expected-note {{in call}}
> +  static_assert(test_memcpy(0, 3, 4) == 4234);
> +  static_assert(test_memcpy(0, 3, 8) == 4234); // expected-error
> {{constant}} expected-note {{in call}}
> +  static_assert(test_memcpy(2, 0, 12) == 4234); // expected-error
> {{constant}} expected-note {{in call}}
> +
> +  static_assert(test_memmove(1, 2, 4) == 1334);
> +  static_assert(test_memmove(2, 1, 4) == 1224);
> +  static_assert(test_memmove(0, 1, 8) == 2334);
> +  static_assert(test_memmove(1, 0, 8) == 1124);
> +  static_assert(test_memmove(1, 2, 1) == 1334); // expected-error
> {{constant}} expected-note {{in call}}
> +  static_assert(test_memmove(0, 3, 4) == 4234);
> +  static_assert(test_memmove(0, 3, 8) == 4234); // expected-error
> {{constant}} expected-note {{in call}}
> +  static_assert(test_memmove(2, 0, 12) == 4234); // expected-error
> {{constant}} expected-note {{in call}}
> +
> +  static_assert(test_wmemcpy(1, 2, 1) == 1334);
> +  static_assert(test_wmemcpy(2, 1, 1) == 1224);
> +  static_assert(test_wmemcpy(0, 1, 2) == 2334); // expected-error
> {{constant}} expected-note {{in call}}
> +  static_assert(test_wmemcpy(1, 0, 2) == 1124); // expected-error
> {{constant}} expected-note {{in call}}
> +  static_assert(test_wmemcpy(1, 2, 1) == 1334);
> +  static_assert(test_wmemcpy(0, 3, 1) == 4234);
> +  static_assert(test_wmemcpy(0, 3, 2) == 4234); // expected-error
> {{constant}} expected-note {{in call}}
> +  static_assert(test_wmemcpy(2, 0, 3) == 4234); // expected-error
> {{constant}} expected-note {{in call}}
> +
> +  static_assert(test_wmemmove(1, 2, 1) == 1334);
> +  static_assert(test_wmemmove(2, 1, 1) == 1224);
> +  static_assert(test_wmemmove(0, 1, 2) == 2334);
> +  static_assert(test_wmemmove(1, 0, 2) == 1124);
> +  static_assert(test_wmemmove(1, 2, 1) == 1334);
> +  static_assert(test_wmemmove(0, 3, 1) == 4234);
> +  static_assert(test_wmemmove(0, 3, 2) == 4234); // expected-error
> {{constant}} expected-note {{in call}}
> +  static_assert(test_wmemmove(2, 0, 3) == 4234); // expected-error
> {{constant}} expected-note {{in call}}
> +
> +  // Copying is permitted for any trivially-copyable type.
> +  struct Trivial { char k; short s; constexpr bool ok() { return k == 3
> && s == 4; } };
> +  constexpr bool test_trivial() {
> +    Trivial arr[3] = {{1, 2}, {3, 4}, {5, 6}};
> +    __builtin_memcpy(arr, arr+1, sizeof(Trivial));
> +    __builtin_memmove(arr+1, arr, 2 * sizeof(Trivial));
> +    return arr[0].ok() && arr[1].ok() && arr[2].ok();
> +  }
> +  static_assert(test_trivial());
> +
> +  // But not for a non-trivially-copyable type.
> +  struct NonTrivial {
> +    constexpr NonTrivial() : n(0) {}
> +    constexpr NonTrivial(const NonTrivial &) : n(1) {}
> +    int n;
> +  };
> +  constexpr bool test_nontrivial_memcpy() { // expected-error {{never
> produces a constant}}
> +    NonTrivial arr[3] = {};
> +    __builtin_memcpy(arr, arr + 1, sizeof(NonTrivial)); // expected-note
> 2{{non-trivially-copyable}}
> +    return true;
> +  }
> +  static_assert(test_nontrivial_memcpy()); // expected-error {{constant}}
> expected-note {{in call}}
> +  constexpr bool test_nontrivial_memmove() { // expected-error {{never
> produces a constant}}
> +    NonTrivial arr[3] = {};
> +    __builtin_memcpy(arr, arr + 1, sizeof(NonTrivial)); // expected-note
> 2{{non-trivially-copyable}}
> +    return true;
> +  }
> +  static_assert(test_nontrivial_memmove()); // expected-error
> {{constant}} expected-note {{in call}}
> +
> +  // Type puns via constant evaluated memcpy are not supported yet.
> +  constexpr float type_pun(const unsigned &n) {
> +    float f = 0.0f;
> +    __builtin_memcpy(&f, &n, 4); // expected-note {{cannot constant
> evaluate 'memcpy' from object of type 'const unsigned int' to object of
> type 'float'}}
> +    return f;
> +  }
> +  static_assert(type_pun(0x3f800000) == 1.0f); // expected-error
> {{constant}} expected-note {{in call}}
> +
> +  // Make sure we're not confused by derived-to-base conversions.
> +  struct Base { int a; };
> +  struct Derived : Base { int b; };
> +  constexpr int test_derived_to_base(int n) {
> +    Derived arr[2] = {1, 2, 3, 4};
> +    Base *p = &arr[0];
> +    Base *q = &arr[1];
> +    __builtin_memcpy(p, q, sizeof(Base) * n); // expected-note {{source
> is not a contiguous array of at least 2 elements of type 'MemcpyEtc::Base'}}
> +    return arr[0].a * 1000 + arr[0].b * 100 + arr[1].a * 10 + arr[1].b;
> +  }
> +  static_assert(test_derived_to_base(0) == 1234);
> +  static_assert(test_derived_to_base(1) == 3234);
> +  // FIXME: We could consider making this work by stripping elements off
> both
> +  // designators until we have a long enough matching size, if both
> designators
> +  // point to the start of their respective final elements.
> +  static_assert(test_derived_to_base(2) == 3434); // expected-error
> {{constant}} expected-note {{in call}}
> +}
>
>
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