[clang][Sema] Fixed Compound Literal is not Constant Expression

[Mr-Anyone]

Added a check for a compound literal hiding inside a function.

fixes #87867

[llvmbot]

@llvm/pr-subscribers-clang

Author: Vincent (Mr-Anyone)

Changes

Added a check for a compound literal hiding inside a function.

fixes #87867

---

Full diff: https://github.com/llvm/llvm-project/pull/143852.diff

3 Files Affected:

• (modified) clang/docs/ReleaseNotes.rst (+2)
• (modified) clang/lib/Sema/SemaExpr.cpp (+12)
• (added) clang/test/Sema/gh87867.c (+33)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index b42d5f8425af6..df1963f19e35f 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -680,6 +680,8 @@ Bug Fixes in This Version
   ``#include`` directive. (#GH138094)
 - Fixed a crash during constant evaluation involving invalid lambda captures
   (#GH138832)
+- Fixed compound literal is not constant expression inside initializer list 
+  (#GH87867)
 - Fixed a crash when instantiating an invalid dependent friend template specialization.
   (#GH139052)
 - Fixed a crash with an invalid member function parameter list with a default
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index c7abbbd6993de..5468d6573b4bb 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -7219,6 +7219,17 @@ Sema::ActOnCompoundLiteral(SourceLocation LParenLoc, ParsedType Ty,
   return BuildCompoundLiteralExpr(LParenLoc, TInfo, RParenLoc, InitExpr);
 }
 
+static bool IsInsideFunction(Scope *S) {
+  while (S) {
+    if (S->isFunctionScope())
+      return true;
+
+    S = S->getParent();
+  }
+
+  return false;
+}
+
 ExprResult
 Sema::BuildCompoundLiteralExpr(SourceLocation LParenLoc, TypeSourceInfo *TInfo,
                                SourceLocation RParenLoc, Expr *LiteralExpr) {
@@ -7281,6 +7292,7 @@ Sema::BuildCompoundLiteralExpr(SourceLocation LParenLoc, TypeSourceInfo *TInfo,
   //   void func(char *para[(int [1]){ 0 }[0]);
   const Scope *S = getCurScope();
   bool IsFileScope = !CurContext->isFunctionOrMethod() &&
+                     !IsInsideFunction(getCurScope()) &&
                      (!S || !S->isFunctionPrototypeScope());
 
   // In C, compound literals are l-values for some reason.
diff --git a/clang/test/Sema/gh87867.c b/clang/test/Sema/gh87867.c
new file mode 100644
index 0000000000000..0568c734424ca
--- /dev/null
+++ b/clang/test/Sema/gh87867.c
@@ -0,0 +1,33 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -std=c23 %s
+
+// Compound literal doesn't need a constant expression inside a initializer-list if it is already inside a function 
+// see: https://github.com/llvm/llvm-project/issues/87867
+int foo(int *a, int b) {
+    return 0;
+}
+
+int x;
+struct{int t;} a = (struct {
+    typeof(foo(&(struct { int t; }){.t = x}.t, 0)) t; // expected-error {{initializer element is not a compile-time constant}}
+}){0};
+
+void inside_a_func(){
+    int x;
+    (void)(struct {
+        typeof(foo(&(struct { int t; }){.t = x}.t, 0)) t;
+    }){0};
+}
+
+// see: https://github.com/llvm/llvm-project/issues/143613
+#define bitcast(type, value) \
+    (((union{ typeof(value) src; type dst; }){ (value) }).dst)
+
+double placeholder = 10.0;
+double bar = bitcast(double, placeholder);  // expected-error {{initializer element is not a compile-time constant}}
+
+int main(void)
+{
+    int foo = 4;
+    foo = bitcast(int, bitcast(double, foo));
+    return 0;
+}

[AaronBallman]

LGTM aside from a nit, thank you for working on this!

[AaronBallman]

Suggested change

	static bool IsInsideFunction(Scope *S) {
	static bool IsContainedByFunctionScope(const Scope *S) {

makes it more clear that we're checking whether the given scope is itself somewhere within a function scope.

[shafik]

@AaronBallman it feels like it makes sense to sink this into Scope just like isInObjCMethodScope()

[AaronBallman]

I can go either way. This is currently the first time we've needed this, so a static function makes sense. But if we need this a second time, then absolutely agreed it should be hoisted into Scope. WDYT?

[Mr-Anyone]

I do see people using this from time to time. I just moved this logic into Scope.

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[AaronBallman]

LGTM!

[Mr-Anyone]

@AaronBallman I don't have merge access. Could you please merge this for me? Thanks.

[AaronBallman]

@AaronBallman I don't have merge access. Could you please merge this for me? Thanks.

Absolutely, thank you for letting me know. :-)