[clang-cl] Add support for [[msvc::constexpr]] C++11 attribute #71300
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@llvm/pr-subscribers-clang @llvm/pr-subscribers-clang-driver Author: Richard Dzenis (RIscRIpt) ChangesAs per agreement with @AaronBallman and @erichkeane, I am re-opening this patch here. The current version of the patch has undergone numerous revisions before it became the version I am sending to GitHub. Below you can find a summary of the history of changes. Initially I submitted this patch to make At first I tried to kind of reverse-engineer it myself, I made several observations, some of them were incorrect. Later, @cpplearner noted: Additionally I asked MSVC team to comment about Further testing and experiments revealed that, unfortunately not all of his points were correct. After some trials and errors, I came up with the following definition of semantics for This doc-note was added to As per this definition, we need to be able to track whether current invocation of Patch is 23.88 KiB, truncated to 20.00 KiB below, full version: https://github.com/llvm/llvm-project/pull/71300.diff 19 Files Affected:
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index afe7e2e79c2d087..ed0bfaf67aee449 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -211,6 +211,8 @@ C23 Feature Support
Non-comprehensive list of changes in this release
-------------------------------------------------
+- The default value of `_MSC_VER` was raised from 1920 to 1933.
+ MSVC 19.33 added undocumented attribute ``[[msvc::constexpr]]``.
* Clang now has a ``__builtin_vectorelements()`` function that determines the number of elements in a vector.
For fixed-sized vectors, e.g., defined via ``__attribute__((vector_size(N)))`` or ARM NEON's vector types
diff --git a/clang/docs/UsersManual.rst b/clang/docs/UsersManual.rst
index edc2bce6a964dc4..b849464e6dc3ca6 100644
--- a/clang/docs/UsersManual.rst
+++ b/clang/docs/UsersManual.rst
@@ -3333,8 +3333,8 @@ default for Windows targets.
For compatibility with existing code that compiles with MSVC, clang defines the
``_MSC_VER`` and ``_MSC_FULL_VER`` macros. When on Windows, these default to
-either the same value as the currently installed version of cl.exe, or ``1920``
-and ``192000000`` (respectively). The ``-fms-compatibility-version=`` flag
+either the same value as the currently installed version of cl.exe, or ``1933``
+and ``193300000`` (respectively). The ``-fms-compatibility-version=`` flag
overrides these values. It accepts a dotted version tuple, such as 19.00.23506.
Changing the MSVC compatibility version makes clang behave more like that
version of MSVC. For example, ``-fms-compatibility-version=19`` will enable
diff --git a/clang/include/clang/Basic/Attr.td b/clang/include/clang/Basic/Attr.td
index 60b549999c155e5..771ac5575e25d8c 100644
--- a/clang/include/clang/Basic/Attr.td
+++ b/clang/include/clang/Basic/Attr.td
@@ -3602,6 +3602,14 @@ def : MutualExclusions<[Owner, Pointer]>;
// Microsoft-related attributes
+def MSConstexpr : InheritableAttr {
+ let LangOpts = [MicrosoftExt];
+ let Spellings = [CXX11<"msvc", "constexpr">];
+ let Subjects = SubjectList<[Function, Stmt], ErrorDiag,
+ "functions and statements">;
+ let Documentation = [MSConstexprDocs];
+}
+
def MSNoVTable : InheritableAttr, TargetSpecificAttr<TargetMicrosoftCXXABI> {
let Spellings = [Declspec<"novtable">];
let Subjects = SubjectList<[CXXRecord]>;
diff --git a/clang/include/clang/Basic/AttrDocs.td b/clang/include/clang/Basic/AttrDocs.td
index 05703df2129f612..ce44bd7d5b21490 100644
--- a/clang/include/clang/Basic/AttrDocs.td
+++ b/clang/include/clang/Basic/AttrDocs.td
@@ -3612,6 +3612,22 @@ an error:
}];
}
+def MSConstexprDocs : Documentation {
+ let Category = DocCatStmt;
+ let Content = [{
+The ``[[msvc::constexpr]]`` attribute can be applied only to a function
+definition or a ``return`` statement. It does not impact function declarations.
+A ``[[msvc::constexpr]]`` function cannot be ``constexpr`` or ``consteval``.
+A ``[[msvc::constexpr]]`` function is treated in the same way as a ``constexpr``
+function if it is evaluated in a constant context of
+``[[msvc::constexpr]] return`` statement.
+Otherwise, it is treated as a regular function.
+
+Semantics of this attribute is enabled only under MSVC compatibility
+(``-fms-compatibility-version``) 19.33 and later.
+ }];
+}
+
def MSNoVTableDocs : Documentation {
let Category = DocCatDecl;
let Content = [{
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 474afc2fb99c1f0..1cfe22227c731da 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -2861,8 +2861,8 @@ def warn_cxx17_compat_constexpr_local_var_no_init : Warning<
"is incompatible with C++ standards before C++20">,
InGroup<CXXPre20Compat>, DefaultIgnore;
def ext_constexpr_function_never_constant_expr : ExtWarn<
- "%select{constexpr|consteval}1 %select{function|constructor}0 never produces a "
- "constant expression">, InGroup<DiagGroup<"invalid-constexpr">>, DefaultError;
+ "%select{constexpr|consteval|[[msvc::constexpr]]}1 %select{function|constructor}0 "
+ "never produces a constant expression">, InGroup<DiagGroup<"invalid-constexpr">>, DefaultError;
def err_attr_cond_never_constant_expr : Error<
"%0 attribute expression never produces a constant expression">;
def err_diagnose_if_invalid_diagnostic_type : Error<
@@ -2884,6 +2884,12 @@ def warn_cxx11_compat_constexpr_body_multiple_return : Warning<
InGroup<CXXPre14Compat>, DefaultIgnore;
def note_constexpr_body_previous_return : Note<
"previous return statement is here">;
+def err_ms_constexpr_not_distinct : Error<
+ "[[msvc::constexpr]] cannot be applied to a %select{constexpr|consteval}0 function %1">;
+def err_ms_constexpr_virtual : Error<"virtual function cannot be [[msvc::constexpr]]">;
+def warn_ms_constexpr_no_effect : Warning<
+ "[[msvc::constexpr]] has effect only on function definitions and return statements">,
+ InGroup<IgnoredAttributes>;
// C++20 function try blocks in constexpr
def ext_constexpr_function_try_block_cxx20 : ExtWarn<
diff --git a/clang/include/clang/Basic/LangOptions.h b/clang/include/clang/Basic/LangOptions.h
index 20a8ada60e0fe51..f5d2cfcafcd198c 100644
--- a/clang/include/clang/Basic/LangOptions.h
+++ b/clang/include/clang/Basic/LangOptions.h
@@ -152,6 +152,7 @@ class LangOptions : public LangOptionsBase {
MSVC2019 = 1920,
MSVC2019_5 = 1925,
MSVC2019_8 = 1928,
+ MSVC2022_3 = 1933,
};
enum SYCLMajorVersion {
diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index b6b1e6617dffaa9..6aa10ac61f87d6a 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -640,6 +640,10 @@ namespace {
return false;
}
+ /// Whether we're in a context where [[msvc::constexpr]] evaluation is
+ /// permitted. See MSConstexprDocs for description of permitted contexts.
+ bool CanEvalMSConstexpr = false;
+
private:
APValue &createLocal(APValue::LValueBase Base, const void *Key, QualType T,
ScopeKind Scope);
@@ -673,6 +677,19 @@ namespace {
private:
llvm::TimeTraceScope TimeScope;
};
+
+ /// RAII object used to change the current ability of
+ /// [[msvc::constexpr]] evaulation.
+ struct MSConstexprContextRAII {
+ CallStackFrame &Frame;
+ bool OldValue;
+ explicit MSConstexprContextRAII(CallStackFrame &Frame, bool Value)
+ : Frame(Frame), OldValue(Frame.CanEvalMSConstexpr) {
+ Frame.CanEvalMSConstexpr = Value;
+ }
+
+ ~MSConstexprContextRAII() { Frame.CanEvalMSConstexpr = OldValue; }
+ };
}
static bool HandleDestruction(EvalInfo &Info, const Expr *E,
@@ -5535,11 +5552,14 @@ static EvalStmtResult EvaluateStmt(StmtResult &Result, EvalInfo &Info,
case Stmt::LabelStmtClass:
return EvaluateStmt(Result, Info, cast<LabelStmt>(S)->getSubStmt(), Case);
- case Stmt::AttributedStmtClass:
- // As a general principle, C++11 attributes can be ignored without
- // any semantic impact.
- return EvaluateStmt(Result, Info, cast<AttributedStmt>(S)->getSubStmt(),
- Case);
+ case Stmt::AttributedStmtClass: {
+ const auto *AS = cast<AttributedStmt>(S);
+ const auto *SS = AS->getSubStmt();
+ MSConstexprContextRAII msConstexprContext(
+ *Info.CurrentCall, hasSpecificAttr<MSConstexprAttr>(AS->getAttrs()) &&
+ isa<ReturnStmt>(SS));
+ return EvaluateStmt(Result, Info, SS, Case);
+ }
case Stmt::CaseStmtClass:
case Stmt::DefaultStmtClass:
@@ -5610,7 +5630,9 @@ static bool CheckConstexprFunction(EvalInfo &Info, SourceLocation CallLoc,
}
// Can we evaluate this function call?
- if (Definition && Definition->isConstexpr() && Body)
+ if (Definition && Body &&
+ (Definition->isConstexpr() || Info.CurrentCall->CanEvalMSConstexpr &&
+ Definition->hasAttr<MSConstexprAttr>()))
return true;
if (Info.getLangOpts().CPlusPlus11) {
diff --git a/clang/lib/Basic/Targets/OSTargets.cpp b/clang/lib/Basic/Targets/OSTargets.cpp
index 627bc912fa23104..899aefa6173acfe 100644
--- a/clang/lib/Basic/Targets/OSTargets.cpp
+++ b/clang/lib/Basic/Targets/OSTargets.cpp
@@ -224,6 +224,9 @@ static void addVisualCDefines(const LangOptions &Opts, MacroBuilder &Builder) {
else if (Opts.CPlusPlus14)
Builder.defineMacro("_MSVC_LANG", "201402L");
}
+
+ if (Opts.isCompatibleWithMSVC(LangOptions::MSVC2022_3))
+ Builder.defineMacro("_MSVC_CONSTEXPR_ATTRIBUTE");
}
if (Opts.MicrosoftExt) {
diff --git a/clang/lib/Driver/ToolChains/MSVC.cpp b/clang/lib/Driver/ToolChains/MSVC.cpp
index 4966d102c51f1ac..9809ae39da2e4e1 100644
--- a/clang/lib/Driver/ToolChains/MSVC.cpp
+++ b/clang/lib/Driver/ToolChains/MSVC.cpp
@@ -787,11 +787,11 @@ VersionTuple MSVCToolChain::computeMSVCVersion(const Driver *D,
if (MSVT.empty() &&
Args.hasFlag(options::OPT_fms_extensions, options::OPT_fno_ms_extensions,
IsWindowsMSVC)) {
- // -fms-compatibility-version=19.20 is default, aka 2019, 16.x
+ // -fms-compatibility-version=19.33 is default, aka 2022, 17.3
// NOTE: when changing this value, also update
// clang/docs/CommandGuide/clang.rst and clang/docs/UsersManual.rst
// accordingly.
- MSVT = VersionTuple(19, 20);
+ MSVT = VersionTuple(19, 33);
}
return MSVT;
}
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 396566a8f10a9b7..e753b721729e51b 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -16163,7 +16163,9 @@ Decl *Sema::ActOnFinishFunctionBody(Decl *dcl, Stmt *Body,
ActivePolicy = &WP;
}
- if (!IsInstantiation && FD && FD->isConstexpr() && !FD->isInvalidDecl() &&
+ if (!IsInstantiation && FD &&
+ (FD->isConstexpr() || FD->hasAttr<MSConstexprAttr>()) &&
+ !FD->isInvalidDecl() &&
!CheckConstexprFunctionDefinition(FD, CheckConstexprKind::Diagnose))
FD->setInvalidDecl();
diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
index cdb769a883550d0..689d69d4b94ae84 100644
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -7337,6 +7337,27 @@ static void handleDeclspecThreadAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
D->addAttr(::new (S.Context) ThreadAttr(S.Context, AL));
}
+static void handleMSConstexprAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
+ if (!S.getLangOpts().isCompatibleWithMSVC(LangOptions::MSVC2022_3)) {
+ S.Diag(AL.getLoc(), diag::warn_unknown_attribute_ignored)
+ << AL << AL.getRange();
+ return;
+ }
+ auto *FD = cast<FunctionDecl>(D);
+ if (FD->isConstexprSpecified() || FD->isConsteval()) {
+ S.Diag(AL.getLoc(), diag::err_ms_constexpr_not_distinct)
+ << FD->isConsteval() << FD;
+ return;
+ }
+ if (auto *MD = dyn_cast<CXXMethodDecl>(FD)) {
+ if (!S.getLangOpts().CPlusPlus20 && MD->isVirtual()) {
+ S.Diag(AL.getLoc(), diag::err_ms_constexpr_virtual);
+ return;
+ }
+ }
+ D->addAttr(::new (S.Context) MSConstexprAttr(S.Context, AL));
+}
+
static void handleAbiTagAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
SmallVector<StringRef, 4> Tags;
for (unsigned I = 0, E = AL.getNumArgs(); I != E; ++I) {
@@ -9439,6 +9460,9 @@ ProcessDeclAttribute(Sema &S, Scope *scope, Decl *D, const ParsedAttr &AL,
case ParsedAttr::AT_Thread:
handleDeclspecThreadAttr(S, D, AL);
break;
+ case ParsedAttr::AT_MSConstexpr:
+ handleMSConstexprAttr(S, D, AL);
+ break;
// HLSL attributes:
case ParsedAttr::AT_HLSLNumThreads:
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 397b7a00e453126..c294c946a254e96 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -2458,9 +2458,12 @@ static bool CheckConstexprFunctionBody(Sema &SemaRef, const FunctionDecl *Dcl,
SmallVector<PartialDiagnosticAt, 8> Diags;
if (Kind == Sema::CheckConstexprKind::Diagnose &&
!Expr::isPotentialConstantExpr(Dcl, Diags)) {
+ int ConstKind = Dcl->hasAttr<MSConstexprAttr>() ? 2
+ : Dcl->isConsteval() ? 1
+ : 0;
SemaRef.Diag(Dcl->getLocation(),
diag::ext_constexpr_function_never_constant_expr)
- << isa<CXXConstructorDecl>(Dcl) << Dcl->isConsteval()
+ << isa<CXXConstructorDecl>(Dcl) << ConstKind
<< Dcl->getNameInfo().getSourceRange();
for (size_t I = 0, N = Diags.size(); I != N; ++I)
SemaRef.Diag(Diags[I].first, Diags[I].second);
diff --git a/clang/lib/Sema/SemaStmtAttr.cpp b/clang/lib/Sema/SemaStmtAttr.cpp
index ad20bc8871f103a..7b8742b7687e031 100644
--- a/clang/lib/Sema/SemaStmtAttr.cpp
+++ b/clang/lib/Sema/SemaStmtAttr.cpp
@@ -322,6 +322,20 @@ static Attr *handleUnlikely(Sema &S, Stmt *St, const ParsedAttr &A,
return ::new (S.Context) UnlikelyAttr(S.Context, A);
}
+static Attr *handleMSConstexprAttr(Sema &S, Stmt *St, const ParsedAttr &A,
+ SourceRange Range) {
+ if (!S.getLangOpts().isCompatibleWithMSVC(LangOptions::MSVC2022_3)) {
+ S.Diag(A.getLoc(), diag::warn_unknown_attribute_ignored)
+ << A << A.getRange();
+ return nullptr;
+ }
+ if (!isa<ReturnStmt>(St)) {
+ S.Diag(A.getLoc(), diag::warn_ms_constexpr_no_effect);
+ return nullptr;
+ }
+ return ::new (S.Context) MSConstexprAttr(S.Context, A);
+}
+
#define WANT_STMT_MERGE_LOGIC
#include "clang/Sema/AttrParsedAttrImpl.inc"
#undef WANT_STMT_MERGE_LOGIC
@@ -523,6 +537,8 @@ static Attr *ProcessStmtAttribute(Sema &S, Stmt *St, const ParsedAttr &A,
return handleLikely(S, St, A, Range);
case ParsedAttr::AT_Unlikely:
return handleUnlikely(S, St, A, Range);
+ case ParsedAttr::AT_MSConstexpr:
+ return handleMSConstexprAttr(S, St, A, Range);
default:
// N.B., ClangAttrEmitter.cpp emits a diagnostic helper that ensures a
// declaration attribute is not written on a statement, but this code is
diff --git a/clang/test/AST/ms-constexpr.cpp b/clang/test/AST/ms-constexpr.cpp
new file mode 100644
index 000000000000000..e85af8494f3344a
--- /dev/null
+++ b/clang/test/AST/ms-constexpr.cpp
@@ -0,0 +1,28 @@
+// RUN: %clang_cc1 -fms-compatibility -fms-compatibility-version=19.33 -std=c++20 -ast-dump -verify %s | FileCheck %s
+// expected-no-diagnostics
+
+// CHECK: used f1 'bool ()'
+// CHECK: MSConstexprAttr 0x{{[0-9a-f]+}} <col:3, col:9>
+[[msvc::constexpr]] bool f1() { return true; }
+
+// CHECK: used constexpr f2 'bool ()'
+// CHECK-NEXT: CompoundStmt 0x{{[0-9a-f]+}} <col:21, col:56>
+// CHECK-NEXT: AttributedStmt 0x{{[0-9a-f]+}} <col:23, col:53>
+// CHECK-NEXT: MSConstexprAttr 0x{{[0-9a-f]+}} <col:25, col:31>
+// CHECK-NEXT: ReturnStmt 0x{{[0-9a-f]+}} <col:43, col:53>
+constexpr bool f2() { [[msvc::constexpr]] return f1(); }
+static_assert(f2());
+
+struct S1 {
+ // CHECK: used vm 'bool ()' virtual
+ // CHECK: MSConstexprAttr 0x{{[0-9a-f]+}} <col:7, col:13>
+ [[msvc::constexpr]] virtual bool vm() { return true; }
+
+ // CHECK: used constexpr cm 'bool ()'
+ // CHECK-NEXT: CompoundStmt 0x{{[0-9a-f]+}} <col:25, col:60>
+ // CHECK-NEXT: AttributedStmt 0x{{[0-9a-f]+}} <col:27, col:57>
+ // CHECK-NEXT: MSConstexprAttr 0x{{[0-9a-f]+}} <col:29, col:35>
+ // CHECK-NEXT: ReturnStmt 0x{{[0-9a-f]+}} <col:47, col:57>
+ constexpr bool cm() { [[msvc::constexpr]] return vm(); }
+};
+static_assert(S1{}.cm());
diff --git a/clang/test/Driver/cl-options.c b/clang/test/Driver/cl-options.c
index 6d929b19e7e2ef8..81d1b907eced188 100644
--- a/clang/test/Driver/cl-options.c
+++ b/clang/test/Driver/cl-options.c
@@ -747,7 +747,7 @@
// Validate that the default triple is used when run an empty tools dir is specified
// RUN: %clang_cl -vctoolsdir "" -### -- %s 2>&1 | FileCheck %s --check-prefix VCTOOLSDIR
-// VCTOOLSDIR: "-triple" "{{[a-zA-Z0-9_-]*}}-pc-windows-msvc19.20.0"
+// VCTOOLSDIR: "-triple" "{{[a-zA-Z0-9_-]*}}-pc-windows-msvc19.33.0"
// Validate that built-in include paths are based on the supplied path
// RUN: %clang_cl --target=aarch64-pc-windows-msvc -vctoolsdir "/fake" -winsdkdir "/foo" -winsdkversion 10.0.12345.0 -### -- %s 2>&1 | FileCheck %s --check-prefix FAKEDIR
@@ -787,7 +787,7 @@
// RUN: %clang_cl -vctoolsdir "" /arm64EC /c -### -- %s 2>&1 | FileCheck --check-prefix=ARM64EC %s
// ARM64EC-NOT: /arm64EC has been overridden by specified target
-// ARM64EC: "-triple" "arm64ec-pc-windows-msvc19.20.0"
+// ARM64EC: "-triple" "arm64ec-pc-windows-msvc19.33.0"
// RUN: %clang_cl -vctoolsdir "" /arm64EC /c -target x86_64-pc-windows-msvc -### -- %s 2>&1 | FileCheck --check-prefix=ARM64EC_OVERRIDE %s
// ARM64EC_OVERRIDE: warning: /arm64EC has been overridden by specified target: x86_64-pc-windows-msvc; option ignored
diff --git a/clang/test/Misc/pragma-attribute-supported-attributes-list.test b/clang/test/Misc/pragma-attribute-supported-attributes-list.test
index f48126775c8685c..67a74f7a4d13b6f 100644
--- a/clang/test/Misc/pragma-attribute-supported-attributes-list.test
+++ b/clang/test/Misc/pragma-attribute-supported-attributes-list.test
@@ -85,6 +85,7 @@
// CHECK-NEXT: LoaderUninitialized (SubjectMatchRule_variable_is_global)
// CHECK-NEXT: Lockable (SubjectMatchRule_record)
// CHECK-NEXT: MIGServerRoutine (SubjectMatchRule_function, SubjectMatchRule_objc_method, SubjectMatchRule_block)
+// CHECK-NEXT: MSConstexpr (SubjectMatchRule_function)
// CHECK-NEXT: MSStruct (SubjectMatchRule_record)
// CHECK-NEXT: MaybeUndef (SubjectMatchRule_variable_is_parameter)
// CHECK-NEXT: MicroMips (SubjectMatchRule_function)
diff --git a/clang/test/SemaCXX/ms-constexpr-invalid.cpp b/clang/test/SemaCXX/ms-constexpr-invalid.cpp
new file mode 100644
index 000000000000000..9e88d8097e02a04
--- /dev/null
+++ b/clang/test/SemaCXX/ms-constexpr-invalid.cpp
@@ -0,0 +1,52 @@
+// RUN: %clang_cc1 -fms-compatibility -fms-compatibility-version=19.33 -std=c++20 -verify %s
+// RUN: %clang_cc1 -fms-compatibility -fms-compatibility-version=19.33 -std=c++17 -verify %s
+
+// Check explicitly invalid code
+
+void runtime() {} // expected-note {{declared here}}
+
+[[msvc::constexpr]] void f0() { runtime(); } // expected-error {{[[msvc::constexpr]] function never produces a constant expression}} \
+ // expected-note {{non-constexpr function 'runtime' cannot be used in a constant expression}}
+[[msvc::constexpr]] constexpr void f1() {} // expected-error {{[[msvc::constexpr]] cannot be applied to a constexpr function 'f1'}}
+#if __cplusplus >= 202202L
+[[msvc::constexpr]] consteval void f2() {} // expected-error {{[[msvc::constexpr]] cannot be applied to a consteval function 'f2'}}
+#endif
+
+struct B1 {};
+struct D1 : virtual B1 { // expected-note {{virtual base class declared here}}
+ [[msvc::constexpr]] D1() {} // expected-error {{constexpr constructor not allowed in struct with virtual base class}}
+};
+
+struct [[msvc::constexpr]] S2{}; // expected-error {{'constexpr' attribute only applies to functions and statements}}
+
+// Check invalid code mixed with valid code
+
+[[msvc::constexpr]] int f4(int x) { return x > 1 ? 1 + f4(x / 2) : 0; } // expected-note {{non-constexpr function 'f4' cannot be used in a constant expression}} \
+ // expected-note {{declared here}} \
+ // expected-note {{declared here}} \
+ // expected-note {{declared here}}
+constexpr bool f5() { [[msvc::constexpr]] return f4(32) == 5; } // expected-note {{in call to 'f4(32)'}}
+static_assert(f5()); // expected-error {{static assertion expression is not an integral constant expression}} \
+ // expected-note {{in call to 'f5()'}}
+
+int f6(int x) { [[msvc::constexpr]] return x > 1 ? 1 + f6(x / 2) : 0; } // expected-note {{declared here}} \
+ // expected-note {{declared here}}
+constexpr bool f7() { [[msvc::constexpr]] return f6(32) == 5; } // expected-error {{constexpr function never produces a constant expression}} \
+ ...
[truncated]
|
|
Initially I replicated semantics of // RUN: %clang_cc1 -fms-compatibility -fms-compatibility-version=19.33 -std=c++20 -ast-dump %s | FileCheck %s
// CHECK: used operator new
// CHECK: MSConstexprAttr 0x{{[0-9a-f]+}} <col:17, col:23>
[[nodiscard]] [[msvc::constexpr]] inline void* __cdecl operator new(decltype(sizeof(void*)), void* p) noexcept { return p; }
// CHECK: used constexpr construct_at
// CHECK: AttributedStmt 0x{{[0-9a-f]+}} <col:46, col:88>
// CHECK-NEXT: MSConstexprAttr 0x{{[0-9a-f]+}} <col:48, col:54>
// CHECK-NEXT: ReturnStmt 0x{{[0-9a-f]+}} <col:66, col:88>
constexpr int* construct_at(int* p, int v) { [[msvc::constexpr]] return ::new (p) int(v); }
constexpr bool check_construct_at() { int x; return *construct_at(&x, 42) == 42; }
static_assert(check_construct_at());However @zygoloid raised a concern over changes in bool IsNothrow = false;
bool IsPlacement = false;
+ bool IsMSConstexpr = Info.CurrentCall->CanEvalMSConstexpr &&
+ OperatorNew->hasAttr<MSConstexprAttr>();
if (OperatorNew->isReservedGlobalPlacementOperator() &&
- Info.CurrentCall->isStdFunction() && !E->isArray()) {
+ (Info.CurrentCall->isStdFunction() || IsMSConstexpr) && !E->isArray()) {
If I could choose, I would opt to fully replicate the behavior of MSVC. However, I also acknowledge the concerns that have been raised. @AaronBallman, @erichkeane, any comments? |
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Discussion initiated by @AaronBallman of one of important design decisions, which was forgotten (?):
Note: in the current implementation I enable |
RIscRIpt
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Oof, sorry, I forgot I should push new changes and rebased changes separately (otherwise "Compare" link does not make sense). If you had checkout |
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Rebased onto main, resolved conflicts, re-run lit locally. |
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@rnk @amykhuang might be interested in reviewing as well. |
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Also, please don't 'force-push', just push an additional commit to your review. It erases history and makes reviewing it about 3x harder since history/context gets lost. |
AaronBallman
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Sorry. I did this, because I am used to such workflow and reviewing range-diff; but to make it work one have to follow strict rule of pushing changes and rebased branch separately (which I failed to do previous time). Edit: I think I see what you mean 😕 |
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Thank you! |
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I don't have write access, but I believe it is ready to be merged. |
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Suggested commit message: Edit: styling/grammar. |
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As per agreement with @AaronBallman and @erichkeane, I am re-opening this patch here. Migrated from differential revision: https://reviews.llvm.org/D134475
The current version of the patch has undergone numerous revisions before it became the version I am sending to GitHub.
Below you can find a summary of the history of changes.
The full history of all comments (excluding code-inline comments) is available in this file:
msvc-constexpr-D134475-comments.md
Initially I submitted this patch to make
[[msvc::constexpr]]visible in the AST, with no semantics, and no tests at all. @AaronBallman has told me that you typically don't accept such patches, so I started figuring out semantics of[[msvc::constexpr]].At first I tried to kind of reverse-engineer it myself, I made several observations, some of them were incorrect.
Later, @cpplearner noted:
Additionally I asked MSVC team to comment about
[[msvc::constexpr]]. Cody Miller from Microsoft has shared semantics of[[msvc::constexpr]]here.Further testing and experiments revealed that, unfortunately not all of his points were correct.
After some trials and errors, I came up with the following definition of semantics for
[[msvc::constexpr]]This doc-note was added to
MSConstexprDocs.As per this definition, we need to be able to track whether current invocation of
[[msvc::constexpr]]function comes from[[msvc::constexpr]] returnstatement, which in turn comes from a constant evaluation context (i.e. aconstexprfunction).Thus I went with the approach, which I saw being used in some other cases: a RAII helper (
MSConstexprContextRAII), and aboolflag inCallStackFrame.