r338455 - [constexpr] Support for constant evaluation of __builtin_memcpy and
Hans Wennborg via cfe-commits
cfe-commits at lists.llvm.org
Wed Aug 1 10:51:50 PDT 2018
We hit this in Chromium too, see crbug.com/869824
I've reverted in r338602
On Wed, Aug 1, 2018 at 5:26 PM, Benjamin Kramer via cfe-commits
<cfe-commits at lists.llvm.org> wrote:
> It's pretty easy to make this crash
>
> $ cat memcpy.c
> void foo() {
> int a[1], b;
> memcpy((char*)a, (const char*)&b, (unsigned long)4);
> }
>
> $ clang memcpy.c
> llvm/include/llvm/ADT/SmallVector.h:178: const_reference
> llvm::SmallVectorTemplateCommon<clang::APValue::LValuePathEntry,
> void>::back() const [T = clang::APValue::LValue
> PathEntry]: Assertion `!empty()' failed.
>
> On Wed, Aug 1, 2018 at 1:35 AM Richard Smith via cfe-commits
> <cfe-commits at lists.llvm.org> wrote:
>>
>> Author: rsmith
>> Date: Tue Jul 31 16:35:09 2018
>> New Revision: 338455
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=338455&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.
>>
>> 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=338455&r1=338454&r2=338455&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/include/clang/Basic/Builtins.def (original)
>> +++ cfe/trunk/include/clang/Basic/Builtins.def Tue Jul 31 16:35:09 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=338455&r1=338454&r2=338455&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/include/clang/Basic/DiagnosticASTKinds.td (original)
>> +++ cfe/trunk/include/clang/Basic/DiagnosticASTKinds.td Tue Jul 31
>> 16:35:09 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=338455&r1=338454&r2=338455&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/lib/AST/ExprConstant.cpp (original)
>> +++ cfe/trunk/lib/AST/ExprConstant.cpp Tue Jul 31 16:35:09 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 +348,13 @@ 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 {
>> + 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 +1732,54 @@ 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 +1991,6 @@ 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 +6164,130 @@ 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)))
>> + return false;
>> + LValue Dest = Result;
>> +
>> + LValue Src;
>> + if (!EvaluatePointer(E->getArg(1), Src, Info))
>> + 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 +8528,6 @@ 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=338455&r1=338454&r2=338455&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/test/CodeGen/builtin-memfns.c (original)
>> +++ cfe/trunk/test/CodeGen/builtin-memfns.c Tue Jul 31 16:35:09 2018
>> @@ -1,5 +1,8 @@
>> // RUN: %clang_cc1 -triple i386-pc-linux-gnu -emit-llvm < %s| FileCheck
>> %s
>>
>> +typedef __WCHAR_TYPE__ wchar_t;
>> +typedef __SIZE_TYPE__ size_t;
>> +
>> // CHECK: @test1
>> // CHECK: call void @llvm.memset.p0i8.i32
>> // CHECK: call void @llvm.memset.p0i8.i32
>> @@ -83,3 +86,17 @@ 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);
>> +}
>> +
>>
>> Modified: cfe/trunk/test/SemaCXX/constexpr-string.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/constexpr-string.cpp?rev=338455&r1=338454&r2=338455&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/test/SemaCXX/constexpr-string.cpp (original)
>> +++ cfe/trunk/test/SemaCXX/constexpr-string.cpp Tue Jul 31 16:35:09 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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