[PATCH] D137826: [clang] Allow comparing pointers to string literals

[Timm Bäder via Phabricator via cfe-commits]

tbaeder created this revision.
tbaeder added reviewers: aaron.ballman, jwakely.
Herald added a project: All.
tbaeder requested review of this revision.
Herald added a project: clang.
Herald added a subscriber: cfe-commits.

This fixes https://github.com/llvm/llvm-project/issues/58754


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D137826

Files:
  clang/lib/AST/ExprConstant.cpp
  clang/test/SemaCXX/builtins.cpp
  clang/test/SemaCXX/constant-expression-cxx11.cpp
  clang/test/SemaCXX/constant-expression-cxx14.cpp


Index: clang/test/SemaCXX/constant-expression-cxx14.cpp
===================================================================
--- clang/test/SemaCXX/constant-expression-cxx14.cpp
+++ clang/test/SemaCXX/constant-expression-cxx14.cpp
@@ -1274,3 +1274,12 @@
     (dbt2.wp = nullptr, 0)
   };
 }
+
+
+constexpr auto name1() { return "name1"; }
+constexpr auto name2() { return "name2"; }
+
+constexpr auto b3 = name1() == name1();
+static_assert(b3, "");
+constexpr auto b4 = name1() == name2();
+static_assert(!b4, "");
Index: clang/test/SemaCXX/constant-expression-cxx11.cpp
===================================================================
--- clang/test/SemaCXX/constant-expression-cxx11.cpp
+++ clang/test/SemaCXX/constant-expression-cxx11.cpp
@@ -358,12 +358,29 @@
 
 extern char externalvar[];
 constexpr bool constaddress = (void *)externalvar == (void *)0x4000UL; // expected-error {{must be initialized by a constant expression}} expected-note {{reinterpret_cast}}
-constexpr bool litaddress = "foo" == "foo"; // expected-error {{must be initialized by a constant expression}}
-// cxx20_2b-warning at -1 {{comparison between two arrays is deprecated}}
+constexpr bool litaddress = "foo" == "foo"; // cxx20_2b-warning {{comparison between two arrays is deprecated}}
 static_assert(0 != "foo", "");
 
 }
 
+constexpr const char *foo(const char *p) { return p; }
+constexpr const char *p1 = "test1";
+constexpr const char *p2 = "test2";
+
+constexpr bool b1 = foo(p1) == foo(p1);
+static_assert(b1, "");
+
+constexpr bool b2 = foo(p1) == foo(p2);
+static_assert(!b2, "");
+
+constexpr const char *name1() { return "name1"; }
+constexpr const char *name2() { return "name2"; }
+
+constexpr auto b3 = name1() == name1();
+static_assert(b3, "");
+constexpr auto b4 = name1() == name2();
+static_assert(!b4, "");
+
 namespace MaterializeTemporary {
 
 constexpr int f(const int &r) { return r; }
Index: clang/test/SemaCXX/builtins.cpp
===================================================================
--- clang/test/SemaCXX/builtins.cpp
+++ clang/test/SemaCXX/builtins.cpp
@@ -47,7 +47,7 @@
 void a(void) {}
 int n;
 void *p = __builtin_function_start(n);               // expected-error {{argument must be a function}}
-static_assert(__builtin_function_start(a) == a, ""); // expected-error {{static assertion expression is not an integral constant expression}}
+static_assert(__builtin_function_start(a) == a, ""); // expected-error {{static assertion failed}}
 } // namespace function_start
 
 void no_ms_builtins() {
Index: clang/lib/AST/ExprConstant.cpp
===================================================================
--- clang/lib/AST/ExprConstant.cpp
+++ clang/lib/AST/ExprConstant.cpp
@@ -12947,13 +12947,12 @@
       if ((!LHSValue.Base && !LHSValue.Offset.isZero()) ||
           (!RHSValue.Base && !RHSValue.Offset.isZero()))
         return Error(E);
-      // It's implementation-defined whether distinct literals will have
-      // distinct addresses. In clang, the result of such a comparison is
-      // unspecified, so it is not a constant expression. However, we do know
-      // that the address of a literal will be non-null.
-      if ((IsLiteralLValue(LHSValue) || IsLiteralLValue(RHSValue)) &&
-          LHSValue.Base && RHSValue.Base)
+
+      // ObjC's @encode()
+      if (isa<ObjCEncodeExpr>(E->getLHS()->IgnoreParenImpCasts()) ||
+          isa<ObjCEncodeExpr>(E->getRHS()->IgnoreParenImpCasts()))
         return Error(E);
+
       // We can't tell whether weak symbols will end up pointing to the same
       // object.
       if (IsWeakLValue(LHSValue) || IsWeakLValue(RHSValue))


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