[clang] Compound Literal Statement Constant Expression Assertion Fix

[Mr-Anyone]

Compound literals initializer-list should be a constant expression if it is defined outside the body of a function.

Emit error instead of falling through tripping assertion error.

fixes #139160

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[llvmbot]

@llvm/pr-subscribers-clang

Author: Vincent (Mr-Anyone)

Changes

Compound literals initializer-list should be a constant expression if it is defined outside the body of a function.

Emit error instead of falling through tripping assertion error.

fixes #139160

---

Full diff: https://github.com/llvm/llvm-project/pull/139479.diff

2 Files Affected:

• (modified) clang/lib/Sema/SemaExpr.cpp (+11)
• (modified) clang/test/SemaCXX/cxx2a-consteval.cpp (+22)

diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index deb8d2edfc5c9..e06b6fc233fcc 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -7220,6 +7220,17 @@ Sema::BuildCompoundLiteralExpr(SourceLocation LParenLoc, TypeSourceInfo *TInfo,
     if (auto ILE = dyn_cast<InitListExpr>(LiteralExpr))
       for (unsigned i = 0, j = ILE->getNumInits(); i != j; i++) {
         Expr *Init = ILE->getInit(i);
+        // C99 6.5.2.5
+        //  "If the compound literal occurs outside the body of a function, the
+        //  initializer list shall consist of constant expressions."
+        if (!Init->isTypeDependent() && !Init->isValueDependent() &&
+            !Init->getType()->isDependentType())
+          if (!Init->isConstantInitializer(Context, false)) {
+            Diag(Init->getExprLoc(), diag::err_init_element_not_constant)
+                << Init->getSourceBitField();
+            return ExprError();
+          }
+
         ILE->setInit(i, ConstantExpr::Create(Context, Init));
       }
 
diff --git a/clang/test/SemaCXX/cxx2a-consteval.cpp b/clang/test/SemaCXX/cxx2a-consteval.cpp
index d9d144cafdbcc..d9932e4dd8241 100644
--- a/clang/test/SemaCXX/cxx2a-consteval.cpp
+++ b/clang/test/SemaCXX/cxx2a-consteval.cpp
@@ -1300,3 +1300,25 @@ void foo() {
 }
 
 }
+
+// https://github.com/llvm/llvm-project/issues/139160
+namespace GH139160{
+  // original test case taken from Github
+  struct A {int x[1]; }; 
+  A f(); // expected-note {{declared here}}
+  typedef int *t[];
+  consteval int* f(int* x) { return x; }
+
+  int ** x = (t){f(f().x)}; // expected-error    {{call to consteval function 'GH139160::f' is not a constant expression}}
+                            // expected-note@-1  {{non-constexpr function 'f' cannot be used in a constant expression}}
+                            // expected-error@-2 {{initializer element is not a compile-time constant}} 
+
+  struct B {int value, value_two;};
+  B make_struct() {return {10, 20};} // expected-note {{declared here}}
+  consteval int get_value(B container) {return container.value;}
+  B result = (B){10, get_value(make_struct())}; // expected-error {{initializer element is not a compile-time constant}} 
+                                                // expected-error@-1 {{call to consteval function 'GH139160::get_value' is not a constant expression}}
+                                                // expected-note@-2  {{non-constexpr function 'make_struct' cannot be used in a constant expression}}
+};
+
+

[cor3ntin]

This is not checking for "outside of the function".
Note that GCC errors on these cases too https://compiler-explorer.com/z/TaqzEdnbe
I think you need to update the comment to better describe the check

[Fznamznon]

There is a if (IsFileScope) 4 lines above.

[Mr-Anyone]

I have moved the comment to the if (IsFileScope), is that alright?

[cor3ntin]

This change needs a release note.
Please add an entry to clang/docs/ReleaseNotes.rst in the section the most adapted to the change, and referencing any Github issue this change fixes. Thanks!

[Fznamznon]

A code style nit, we try to add comments explaining the values with parameter name

Suggested change

	if (!Init->isConstantInitializer(Context, false)) {
	if (!Init->isConstantInitializer(Context, /*IsForRef=*/ false)) {

[Mr-Anyone]

done, thanks.

[Fznamznon]

There is a if (IsFileScope) 4 lines above.

[AaronBallman]

I don't think you need the check for !Init->getType()->isDependentType() because computeDependence() on the expression should already account for that, shouldn't it?

[Mr-Anyone]

I don't think you need the check for !Init->getType()->isDependentType() because computeDependence() on the expression should already account for that, shouldn't it?

You're absolutely right—I just removed that check. Thanks!

[AaronBallman]

Just a minor nit from me, otherwise LG!

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