[clang] [clang][ExprConst] Can't be past an invalid LValue designator (PR #84293)

[Timm Baeder via cfe-commits]

https://github.com/tbaederr updated https://github.com/llvm/llvm-project/pull/84293

>From 8dda4c1d6186c8d0ecd6b233f1bd636133056f02 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Timm=20B=C3=A4der?= <tbaeder at redhat.com>
Date: Thu, 7 Mar 2024 10:14:03 +0100
Subject: [PATCH] [clang][ExprConst] Can't be past an invalid LValue designator

---
 clang/lib/AST/ExprConstant.cpp        |  7 ++++++-
 clang/test/AST/Interp/c.c             |  4 ++--
 clang/test/Sema/const-eval.c          |  3 +--
 clang/test/Sema/constexpr-void-cast.c | 14 ++++++++++++++
 4 files changed, 23 insertions(+), 5 deletions(-)
 create mode 100644 clang/test/Sema/constexpr-void-cast.c

diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index d8ca35740fbc35..bc8de9d08542cd 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -9211,7 +9211,8 @@ bool PointerExprEvaluator::VisitCastExpr(const CastExpr *E) {
            Info.getLangOpts().CPlusPlus26)) {
         // Permitted.
       } else {
-        if (SubExpr->getType()->isVoidPointerType()) {
+        if (SubExpr->getType()->isVoidPointerType() &&
+            Info.getLangOpts().CPlusPlus) {
           if (HasValidResult)
             CCEDiag(E, diag::note_constexpr_invalid_void_star_cast)
                 << SubExpr->getType() << Info.getLangOpts().CPlusPlus26
@@ -12899,6 +12900,10 @@ static bool isOnePastTheEndOfCompleteObject(const ASTContext &Ctx,
   if (Ty->isIncompleteType())
     return true;
 
+  // Can't be past the end of an invalid object.
+  if (LV.getLValueDesignator().Invalid)
+    return false;
+
   // We're a past-the-end pointer if we point to the byte after the object,
   // no matter what our type or path is.
   auto Size = Ctx.getTypeSizeInChars(Ty);
diff --git a/clang/test/AST/Interp/c.c b/clang/test/AST/Interp/c.c
index 8de6139efbea09..bd6a5d458b61ac 100644
--- a/clang/test/AST/Interp/c.c
+++ b/clang/test/AST/Interp/c.c
@@ -66,11 +66,11 @@ _Static_assert((&a - 100) != 0, ""); // pedantic-ref-warning {{is a GNU extensio
                                      // pedantic-ref-note {{-100 of non-array}} \
                                      // pedantic-expected-note {{-100 of non-array}}
 /// extern variable of a composite type.
-/// FIXME: The 'cast from void*' note is missing in the new interpreter.
+/// FIXME: The 'this conversion is not allowed' note is missing in the new interpreter.
 extern struct Test50S Test50;
 _Static_assert(&Test50 != (void*)0, ""); // all-warning {{always true}} \
                                          // pedantic-ref-warning {{is a GNU extension}} \
-                                         // pedantic-ref-note {{cast from 'void *' is not allowed}} \
+                                         // pedantic-ref-note {{this conversion is not allowed in a constant expression}} \
                                          // pedantic-expected-warning {{is a GNU extension}}
 
 struct y {int x,y;};
diff --git a/clang/test/Sema/const-eval.c b/clang/test/Sema/const-eval.c
index 2e38d5e23c208a..e358aceaad5a43 100644
--- a/clang/test/Sema/const-eval.c
+++ b/clang/test/Sema/const-eval.c
@@ -134,8 +134,7 @@ void PR21945(void) { int i = (({}), 0l); }
 
 void PR24622(void);
 struct PR24622 {} pr24622;
-EVAL_EXPR(52, &pr24622 == (void *)&PR24622); // expected-error {{not an integer constant expression}}
-                                             // expected-note at -1 {{past the end}}
+EVAL_EXPR(52, &pr24622 == (void *)&PR24622);
 
 // We evaluate these by providing 2s' complement semantics in constant
 // expressions, like we do for integers.
diff --git a/clang/test/Sema/constexpr-void-cast.c b/clang/test/Sema/constexpr-void-cast.c
new file mode 100644
index 00000000000000..c5caa3b9e58feb
--- /dev/null
+++ b/clang/test/Sema/constexpr-void-cast.c
@@ -0,0 +1,14 @@
+// RUN: %clang_cc1 -x c -fsyntax-only %s -verify=c
+// RUN: %clang_cc1 -x c -fsyntax-only %s -pedantic -verify=c-pedantic
+//
+// RUN: %clang_cc1 -x c++ -fsyntax-only %s -verify=cxx
+// RUN: %clang_cc1 -x c++ -fsyntax-only %s -pedantic -verify=cxx-pedantic
+
+// c-no-diagnostics
+// cxx-no-diagnostics
+
+void f(void);
+struct S {char c;} s;
+_Static_assert(&s != (void *)&f, ""); // c-pedantic-warning {{not an integer constant expression}} \
+                                      // c-pedantic-note {{this conversion is not allowed in a constant expression}} \
+                                      // cxx-pedantic-warning {{'_Static_assert' is a C11 extension}}