[clang-cl] Self instantiation does not work in a constant expression #108962

VladimirShchigolev · 2024-09-17T11:19:01Z

Consider the following example:

template <int I = 0>
struct S {
	static constexpr int A = I;
	static constexpr int B = S<>::A;
};
static_assert(S<1>::B == 0, "S<1>::B should be 0");

Latest MSVC (14.41) is able to compile this:

C:\test>cl.exe /c example.cpp
Microsoft (R) C/C++ Optimizing Compiler Version 19.41.34120 for x64
Copyright (C) Microsoft Corporation.  All rights reserved.

example.cpp

However clang-cl fails to compile:

C:\test>clang-cl.exe example.cpp
C:\test\example.cpp(4,30): error: implicit instantiation of
	  template 'S<>' within its own definition
	4 |     static constexpr int B = S<>::A;
	  |                              ^
C:\test\example.cpp(4,26): error: constexpr variable 'B' must
	  be initialized by a constant expression
	4 |     static constexpr int B = S<>::A;
	  |                          ^
	  |                            = 0
2 errors generated.

Here is a draft patch that I tried to make while working at #47033. It does not work - it removes the errors, but the assert fails. Maybe it will help.

Parent: 520ddf22b2270dc092dbdbd391b1c02c403b475a ([TableGen] Remove duplicate code in applyMnemonicAliases when target uses DefaultAsmParserVariant. (#108494))

------------------------- clang/lib/Sema/SemaDecl.cpp -------------------------
index 3c6a0dff798f..6a12ed82894d 100644
@@ -352,7 +352,26 @@ ParsedType Sema::getTypeName(const IdentifierInfo &II, SourceLocation NameLoc,
       return nullptr;
     }
 
-    if (!LookupCtx->isDependentContext() &&
+    CXXRecordDecl *DeclFromScope = nullptr, *DeclFromScopeSpec = nullptr;
+    if (S->getLookupEntity())
+      DeclFromScope = dyn_cast_or_null<CXXRecordDecl>(S->getLookupEntity());
+
+    if (SS->isValid()) {
+ 	    auto ClassTemplateSpecDecl = 
+ 	        dyn_cast_or_null<ClassTemplateSpecializationDecl>(
+ 		      SS->getScopeRep()->getAsRecordDecl());
+  	  if (ClassTemplateSpecDecl && 
+    		  ClassTemplateSpecDecl->getSpecializedTemplate()) {
+        DeclFromScopeSpec = ClassTemplateSpecDecl->
+ 		    getSpecializedTemplate()->getTemplatedDecl();
+  	  }
+    }
+	
+    if (getLangOpts().MSVCCompat && DeclFromScope && 
+  		  DeclFromScope == DeclFromScopeSpec) {
+      LookupCtx = nullptr;
+  		SS = nullptr;
+    } else if (!LookupCtx->isDependentContext() &&
         RequireCompleteDeclContext(*SS, LookupCtx))
       return nullptr;
   }

------------------------ clang/lib/Sema/SemaLookup.cpp ------------------------
index d3d4bf27ae72..de7b7fbba9b3 100644
@@ -2695,6 +2695,25 @@ bool Sema::LookupParsedName(LookupResult &R, Scope *S, CXXScopeSpec *SS,
             ObjectType->castAs<TagType>()->isBeingDefined()) &&
            "Caller should have completed object type");
   } else if (SS && SS->isNotEmpty()) {
+    CXXRecordDecl *DeclFromScope = nullptr, *DeclFromScopeSpec = nullptr;
+    if (S->getLookupEntity())
+      DeclFromScope = dyn_cast_or_null<CXXRecordDecl>(S->getLookupEntity());
+
+    if (SS->isValid()) {
+ 	    auto ClassTemplateSpecDecl = 
+ 	        dyn_cast_or_null<ClassTemplateSpecializationDecl>(
+ 		      SS->getScopeRep()->getAsRecordDecl());
+  	  if (ClassTemplateSpecDecl && 
+    		  ClassTemplateSpecDecl->getSpecializedTemplate()) {
+        DeclFromScopeSpec = ClassTemplateSpecDecl->
+ 		    getSpecializedTemplate()->getTemplatedDecl();
+  	  }
+    }
+	
+    if (getLangOpts().MSVCCompat && DeclFromScope && 
+  		  DeclFromScope == DeclFromScopeSpec)
+      return LookupName(R, S, AllowBuiltinCreation);
+        
     // This nested-name-specifier occurs after another nested-name-specifier,
     // so long into the context associated with the prior nested-name-specifier.
     if ((DC = computeDeclContext(*SS, EnteringContext))) {

The text was updated successfully, but these errors were encountered:

llvmbot · 2024-09-17T12:49:12Z

@llvm/issue-subscribers-c-1

Author: None (VladimirShchigolev)

Consider the following example: ``` template <int I = 0> struct S { static constexpr int A = I; static constexpr int B = S<>::A; }; static_assert(S<1>::B == 0, "S<1>::B should be 0"); ```

Latest MSVC (14.41) is able to compile this:

C:\test&gt;cl.exe /c example.cpp
Microsoft (R) C/C++ Optimizing Compiler Version 19.41.34120 for x64
Copyright (C) Microsoft Corporation.  All rights reserved.

example.cpp

However clang-cl fails to compile:

C:\test&gt;clang-cl.exe example.cpp
C:\test\example.cpp(4,30): error: implicit instantiation of
	  template 'S&lt;&gt;' within its own definition
	4 |     static constexpr int B = S&lt;&gt;::A;
	  |                              ^
C:\test\example.cpp(4,26): error: constexpr variable 'B' must
	  be initialized by a constant expression
	4 |     static constexpr int B = S&lt;&gt;::A;
	  |                          ^
	  |                            = 0
2 errors generated.

Here is a draft patch that I tried to make while working at #47033. It does not work - it removes the errors, but the assert fails. Maybe it will help.

Parent: 520ddf22b2270dc092dbdbd391b1c02c403b475a ([TableGen] Remove duplicate code in applyMnemonicAliases when target uses DefaultAsmParserVariant. (#<!-- -->108494))

------------------------- clang/lib/Sema/SemaDecl.cpp -------------------------
index 3c6a0dff798f..6a12ed82894d 100644
@@ -352,7 +352,26 @@ ParsedType Sema::getTypeName(const IdentifierInfo &amp;II, SourceLocation NameLoc,
       return nullptr;
     }
 
-    if (!LookupCtx-&gt;isDependentContext() &amp;&amp;
+    CXXRecordDecl *DeclFromScope = nullptr, *DeclFromScopeSpec = nullptr;
+    if (S-&gt;getLookupEntity())
+      DeclFromScope = dyn_cast_or_null&lt;CXXRecordDecl&gt;(S-&gt;getLookupEntity());
+
+    if (SS-&gt;isValid()) {
+ 	    auto ClassTemplateSpecDecl = 
+ 	        dyn_cast_or_null&lt;ClassTemplateSpecializationDecl&gt;(
+ 		      SS-&gt;getScopeRep()-&gt;getAsRecordDecl());
+  	  if (ClassTemplateSpecDecl &amp;&amp; 
+    		  ClassTemplateSpecDecl-&gt;getSpecializedTemplate()) {
+        DeclFromScopeSpec = ClassTemplateSpecDecl-&gt;
+ 		    getSpecializedTemplate()-&gt;getTemplatedDecl();
+  	  }
+    }
+	
+    if (getLangOpts().MSVCCompat &amp;&amp; DeclFromScope &amp;&amp; 
+  		  DeclFromScope == DeclFromScopeSpec) {
+      LookupCtx = nullptr;
+  		SS = nullptr;
+    } else if (!LookupCtx-&gt;isDependentContext() &amp;&amp;
         RequireCompleteDeclContext(*SS, LookupCtx))
       return nullptr;
   }

------------------------ clang/lib/Sema/SemaLookup.cpp ------------------------
index d3d4bf27ae72..de7b7fbba9b3 100644
@@ -2695,6 +2695,25 @@ bool Sema::LookupParsedName(LookupResult &amp;R, Scope *S, CXXScopeSpec *SS,
             ObjectType-&gt;castAs&lt;TagType&gt;()-&gt;isBeingDefined()) &amp;&amp;
            "Caller should have completed object type");
   } else if (SS &amp;&amp; SS-&gt;isNotEmpty()) {
+    CXXRecordDecl *DeclFromScope = nullptr, *DeclFromScopeSpec = nullptr;
+    if (S-&gt;getLookupEntity())
+      DeclFromScope = dyn_cast_or_null&lt;CXXRecordDecl&gt;(S-&gt;getLookupEntity());
+
+    if (SS-&gt;isValid()) {
+ 	    auto ClassTemplateSpecDecl = 
+ 	        dyn_cast_or_null&lt;ClassTemplateSpecializationDecl&gt;(
+ 		      SS-&gt;getScopeRep()-&gt;getAsRecordDecl());
+  	  if (ClassTemplateSpecDecl &amp;&amp; 
+    		  ClassTemplateSpecDecl-&gt;getSpecializedTemplate()) {
+        DeclFromScopeSpec = ClassTemplateSpecDecl-&gt;
+ 		    getSpecializedTemplate()-&gt;getTemplatedDecl();
+  	  }
+    }
+	
+    if (getLangOpts().MSVCCompat &amp;&amp; DeclFromScope &amp;&amp; 
+  		  DeclFromScope == DeclFromScopeSpec)
+      return LookupName(R, S, AllowBuiltinCreation);
+        
     // This nested-name-specifier occurs after another nested-name-specifier,
     // so long into the context associated with the prior nested-name-specifier.
     if ((DC = computeDeclContext(*SS, EnteringContext))) {

llvmbot · 2024-09-17T12:49:15Z

@llvm/issue-subscribers-clang-frontend

Author: None (VladimirShchigolev)

Consider the following example: ``` template <int I = 0> struct S { static constexpr int A = I; static constexpr int B = S<>::A; }; static_assert(S<1>::B == 0, "S<1>::B should be 0"); ```

Latest MSVC (14.41) is able to compile this:

C:\test&gt;cl.exe /c example.cpp
Microsoft (R) C/C++ Optimizing Compiler Version 19.41.34120 for x64
Copyright (C) Microsoft Corporation.  All rights reserved.

example.cpp

However clang-cl fails to compile:

C:\test&gt;clang-cl.exe example.cpp
C:\test\example.cpp(4,30): error: implicit instantiation of
	  template 'S&lt;&gt;' within its own definition
	4 |     static constexpr int B = S&lt;&gt;::A;
	  |                              ^
C:\test\example.cpp(4,26): error: constexpr variable 'B' must
	  be initialized by a constant expression
	4 |     static constexpr int B = S&lt;&gt;::A;
	  |                          ^
	  |                            = 0
2 errors generated.

Here is a draft patch that I tried to make while working at #47033. It does not work - it removes the errors, but the assert fails. Maybe it will help.

Parent: 520ddf22b2270dc092dbdbd391b1c02c403b475a ([TableGen] Remove duplicate code in applyMnemonicAliases when target uses DefaultAsmParserVariant. (#<!-- -->108494))

------------------------- clang/lib/Sema/SemaDecl.cpp -------------------------
index 3c6a0dff798f..6a12ed82894d 100644
@@ -352,7 +352,26 @@ ParsedType Sema::getTypeName(const IdentifierInfo &amp;II, SourceLocation NameLoc,
       return nullptr;
     }
 
-    if (!LookupCtx-&gt;isDependentContext() &amp;&amp;
+    CXXRecordDecl *DeclFromScope = nullptr, *DeclFromScopeSpec = nullptr;
+    if (S-&gt;getLookupEntity())
+      DeclFromScope = dyn_cast_or_null&lt;CXXRecordDecl&gt;(S-&gt;getLookupEntity());
+
+    if (SS-&gt;isValid()) {
+ 	    auto ClassTemplateSpecDecl = 
+ 	        dyn_cast_or_null&lt;ClassTemplateSpecializationDecl&gt;(
+ 		      SS-&gt;getScopeRep()-&gt;getAsRecordDecl());
+  	  if (ClassTemplateSpecDecl &amp;&amp; 
+    		  ClassTemplateSpecDecl-&gt;getSpecializedTemplate()) {
+        DeclFromScopeSpec = ClassTemplateSpecDecl-&gt;
+ 		    getSpecializedTemplate()-&gt;getTemplatedDecl();
+  	  }
+    }
+	
+    if (getLangOpts().MSVCCompat &amp;&amp; DeclFromScope &amp;&amp; 
+  		  DeclFromScope == DeclFromScopeSpec) {
+      LookupCtx = nullptr;
+  		SS = nullptr;
+    } else if (!LookupCtx-&gt;isDependentContext() &amp;&amp;
         RequireCompleteDeclContext(*SS, LookupCtx))
       return nullptr;
   }

------------------------ clang/lib/Sema/SemaLookup.cpp ------------------------
index d3d4bf27ae72..de7b7fbba9b3 100644
@@ -2695,6 +2695,25 @@ bool Sema::LookupParsedName(LookupResult &amp;R, Scope *S, CXXScopeSpec *SS,
             ObjectType-&gt;castAs&lt;TagType&gt;()-&gt;isBeingDefined()) &amp;&amp;
            "Caller should have completed object type");
   } else if (SS &amp;&amp; SS-&gt;isNotEmpty()) {
+    CXXRecordDecl *DeclFromScope = nullptr, *DeclFromScopeSpec = nullptr;
+    if (S-&gt;getLookupEntity())
+      DeclFromScope = dyn_cast_or_null&lt;CXXRecordDecl&gt;(S-&gt;getLookupEntity());
+
+    if (SS-&gt;isValid()) {
+ 	    auto ClassTemplateSpecDecl = 
+ 	        dyn_cast_or_null&lt;ClassTemplateSpecializationDecl&gt;(
+ 		      SS-&gt;getScopeRep()-&gt;getAsRecordDecl());
+  	  if (ClassTemplateSpecDecl &amp;&amp; 
+    		  ClassTemplateSpecDecl-&gt;getSpecializedTemplate()) {
+        DeclFromScopeSpec = ClassTemplateSpecDecl-&gt;
+ 		    getSpecializedTemplate()-&gt;getTemplatedDecl();
+  	  }
+    }
+	
+    if (getLangOpts().MSVCCompat &amp;&amp; DeclFromScope &amp;&amp; 
+  		  DeclFromScope == DeclFromScopeSpec)
+      return LookupName(R, S, AllowBuiltinCreation);
+        
     // This nested-name-specifier occurs after another nested-name-specifier,
     // so long into the context associated with the prior nested-name-specifier.
     if ((DC = computeDeclContext(*SS, EnteringContext))) {

safocl · 2025-01-12T11:38:13Z

static constexpr int B = S<>::A;

static constexpr int B = S::A;

<source>:6:15: error: static assertion failed due to requirement 'S<1>::B == 0': S<1>::B should be 0
    6 | static_assert(S<1>::B == 0, "S<1>::B should be 0");
      |               ^~~~~~~~~~~~
<source>:6:23: note: expression evaluates to '1 == 0'
    6 | static_assert(S<1>::B == 0, "S<1>::B should be 0");
      |               ~~~~~~~~^~~~
1 error generated.
Compiler returned: 1

github-actions bot added the new issue label Sep 17, 2024

RIscRIpt added c++ clang:frontend Language frontend issues, e.g. anything involving "Sema" clang-cl `clang-cl` driver. Don't use for other compiler parts labels Sep 17, 2024

EugeneZelenko added constexpr Anything related to constant evaluation and removed new issue clang-cl `clang-cl` driver. Don't use for other compiler parts labels Sep 17, 2024

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[clang-cl] Self instantiation does not work in a constant expression #108962

[clang-cl] Self instantiation does not work in a constant expression #108962

VladimirShchigolev commented Sep 17, 2024

llvmbot commented Sep 17, 2024

llvmbot commented Sep 17, 2024

safocl commented Jan 12, 2025

[clang-cl] Self instantiation does not work in a constant expression #108962

[clang-cl] Self instantiation does not work in a constant expression #108962

Comments

VladimirShchigolev commented Sep 17, 2024

llvmbot commented Sep 17, 2024

llvmbot commented Sep 17, 2024

safocl commented Jan 12, 2025