PR for llvm/llvm-project#80150

[llvmbot]

resolves #80150

[llvmbot]

@cor3ntin What do you think about merging this PR to the release branch?

[llvmbot]

@llvm/pr-subscribers-clang

Author: None (llvmbot)

Changes

resolves llvm/llvm-project#80150

---

Full diff: https://github.com/llvm/llvm-project/pull/80151.diff

2 Files Affected:

• (modified) clang/lib/Sema/SemaTemplate.cpp (+24-20)
• (modified) clang/test/CoverageMapping/templates.cpp (+13)

diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index 9bfa71dc8bcf1..a381d876a54c6 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -7412,9 +7412,9 @@ ExprResult Sema::CheckTemplateArgument(NonTypeTemplateParmDecl *Param,
     if (ArgResult.isInvalid())
       return ExprError();
 
-    // Prior to C++20, enforce restrictions on possible template argument
-    // values.
-    if (!getLangOpts().CPlusPlus20 && Value.isLValue()) {
+    if (Value.isLValue()) {
+      APValue::LValueBase Base = Value.getLValueBase();
+      auto *VD = const_cast<ValueDecl *>(Base.dyn_cast<const ValueDecl *>());
       //   For a non-type template-parameter of pointer or reference type,
       //   the value of the constant expression shall not refer to
       assert(ParamType->isPointerType() || ParamType->isReferenceType() ||
@@ -7423,8 +7423,6 @@ ExprResult Sema::CheckTemplateArgument(NonTypeTemplateParmDecl *Param,
       // -- a string literal
       // -- the result of a typeid expression, or
       // -- a predefined __func__ variable
-      APValue::LValueBase Base = Value.getLValueBase();
-      auto *VD = const_cast<ValueDecl *>(Base.dyn_cast<const ValueDecl *>());
       if (Base &&
           (!VD ||
            isa<LifetimeExtendedTemporaryDecl, UnnamedGlobalConstantDecl>(VD))) {
@@ -7432,24 +7430,30 @@ ExprResult Sema::CheckTemplateArgument(NonTypeTemplateParmDecl *Param,
             << Arg->getSourceRange();
         return ExprError();
       }
-      // -- a subobject [until C++20]
-      if (Value.hasLValuePath() && Value.getLValuePath().size() == 1 &&
-          VD && VD->getType()->isArrayType() &&
+
+      if (Value.hasLValuePath() && Value.getLValuePath().size() == 1 && VD &&
+          VD->getType()->isArrayType() &&
           Value.getLValuePath()[0].getAsArrayIndex() == 0 &&
           !Value.isLValueOnePastTheEnd() && ParamType->isPointerType()) {
-        // Per defect report (no number yet):
-        //   ... other than a pointer to the first element of a complete array
-        //       object.
-      } else if (!Value.hasLValuePath() || Value.getLValuePath().size() ||
-                 Value.isLValueOnePastTheEnd()) {
-        Diag(StartLoc, diag::err_non_type_template_arg_subobject)
-          << Value.getAsString(Context, ParamType);
-        return ExprError();
+        SugaredConverted = TemplateArgument(VD, ParamType);
+        CanonicalConverted = TemplateArgument(
+            cast<ValueDecl>(VD->getCanonicalDecl()), CanonParamType);
+        return ArgResult.get();
+      }
+
+      // -- a subobject [until C++20]
+      if (!getLangOpts().CPlusPlus20) {
+        if (!Value.hasLValuePath() || Value.getLValuePath().size() ||
+            Value.isLValueOnePastTheEnd()) {
+          Diag(StartLoc, diag::err_non_type_template_arg_subobject)
+              << Value.getAsString(Context, ParamType);
+          return ExprError();
+        }
+        assert((VD || !ParamType->isReferenceType()) &&
+               "null reference should not be a constant expression");
+        assert((!VD || !ParamType->isNullPtrType()) &&
+               "non-null value of type nullptr_t?");
       }
-      assert((VD || !ParamType->isReferenceType()) &&
-             "null reference should not be a constant expression");
-      assert((!VD || !ParamType->isNullPtrType()) &&
-             "non-null value of type nullptr_t?");
     }
 
     if (Value.isAddrLabelDiff())
diff --git a/clang/test/CoverageMapping/templates.cpp b/clang/test/CoverageMapping/templates.cpp
index 7010edbc32c34..143e566a33cb8 100644
--- a/clang/test/CoverageMapping/templates.cpp
+++ b/clang/test/CoverageMapping/templates.cpp
@@ -19,3 +19,16 @@ int main() {
   func<bool>(true);
   return 0;
 }
+
+namespace structural_value_crash {
+  template <int* p>
+  void tpl_fn() {
+    (void)p;
+  }
+
+  int arr[] = {1, 2, 3};
+
+  void test() {
+    tpl_fn<arr>();
+  }
+}

[cor3ntin]

This affects downstream projects already, we should backport.
(It's mostly a partial revert of a recent patch)