[clang] de2fad3 - [Clang] Fix dependent expression handling for assumptions (#115646)

[via cfe-commits]

Author: Younan Zhang
Date: 2024-11-12T09:45:33+08:00
New Revision: de2fad32513f7420988df1cf99aff90e0a067469

URL: https://github.com/llvm/llvm-project/commit/de2fad32513f7420988df1cf99aff90e0a067469
DIFF: https://github.com/llvm/llvm-project/commit/de2fad32513f7420988df1cf99aff90e0a067469.diff

LOG: [Clang] Fix dependent expression handling for assumptions (#115646)

The function definition instantiation assumes any declarations used
inside are already transformed before transforming the body, so we need
to preserve the transformed expression of CXXAssumeAttr even if it is
not a constant expression. Moreover, the full expression of the
assumption should also entail a potential lambda capture transformation,
hence the call to ActOnFinishFullExpr() after TransformExpr().

Fixes #114787

Added: 
    

Modified: 
    clang/docs/ReleaseNotes.rst
    clang/lib/Sema/SemaTemplateInstantiate.cpp
    clang/test/SemaCXX/cxx23-assume.cpp

Removed: 
    


################################################################################
diff  --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index e235a04f78112b..4ef48bed58d95c 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -652,6 +652,8 @@ Bug Fixes to C++ Support
   an implicitly instantiated class template specialization. (#GH51051)
 - Fixed an assertion failure caused by invalid enum forward declarations. (#GH112208)
 - Name independent data members were not correctly initialized from default member initializers. (#GH114069)
+- Fixed expression transformation for ``[[assume(...)]]``, allowing using pack indexing expressions within the
+  assumption if they also occur inside of a dependent lambda. (#GH114787)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^

diff  --git a/clang/lib/Sema/SemaTemplateInstantiate.cpp b/clang/lib/Sema/SemaTemplateInstantiate.cpp
index 9e76b60fd509c7..3a3b5984fe740d 100644
--- a/clang/lib/Sema/SemaTemplateInstantiate.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiate.cpp
@@ -2196,11 +2196,18 @@ TemplateInstantiator::TransformCXXAssumeAttr(const CXXAssumeAttr *AA) {
   if (!Res.isUsable())
     return AA;
 
-  Res = getSema().BuildCXXAssumeExpr(Res.get(), AA->getAttrName(),
-                                     AA->getRange());
+  Res = getSema().ActOnFinishFullExpr(Res.get(),
+                                      /*DiscardedValue=*/false);
   if (!Res.isUsable())
     return AA;
 
+  if (!(Res.get()->getDependence() & ExprDependence::TypeValueInstantiation)) {
+    Res = getSema().BuildCXXAssumeExpr(Res.get(), AA->getAttrName(),
+                                       AA->getRange());
+    if (!Res.isUsable())
+      return AA;
+  }
+
   return CXXAssumeAttr::CreateImplicit(getSema().Context, Res.get(),
                                        AA->getRange());
 }

diff  --git a/clang/test/SemaCXX/cxx23-assume.cpp b/clang/test/SemaCXX/cxx23-assume.cpp
index eeae59daea3f70..7f80cdfe7d4523 100644
--- a/clang/test/SemaCXX/cxx23-assume.cpp
+++ b/clang/test/SemaCXX/cxx23-assume.cpp
@@ -2,6 +2,8 @@
 // RUN: %clang_cc1 -std=c++20 -pedantic -x c++ %s -verify=ext,expected
 // RUN: %clang_cc1 -std=c++23  -x c++ %s -verify -fexperimental-new-constant-interpreter
 // RUN: %clang_cc1 -std=c++20 -pedantic -x c++ %s -verify=ext,expected -fexperimental-new-constant-interpreter
+// RUN: %clang_cc1 -std=c++26  -x c++ %s -verify
+// RUN: %clang_cc1 -std=c++26  -x c++ %s -verify -fexperimental-new-constant-interpreter
 
 struct A{};
 struct B{ explicit operator bool() { return true; } };
@@ -167,3 +169,29 @@ int foo () {
     __attribute__((assume (a < b)));
 }
 }
+
+namespace GH114787 {
+
+// FIXME: Correct the C++26 value
+#if __cplusplus >= 202400L
+
+constexpr int test(auto... xs) {
+  // FIXME: Investigate why addresses of PackIndexingExprs are printed for the next
+  // 'in call to' note.
+  return [&]<int I>() { // expected-note {{in call to}}
+    [[assume(
+      xs...[I] == 2
+    )]];
+    [[assume(
+      xs...[I + 1] == 0 // expected-note {{assumption evaluated to false}}
+    )]];
+    return xs...[I];
+  }.template operator()<1>();
+}
+
+static_assert(test(1, 2, 3, 5, 6) == 2); // expected-error {{not an integral constant expression}} \
+                                         // expected-note {{in call to}}
+
+#endif
+
+} // namespace GH114787