[PATCH] D131155: [clang] Expand array expressions if the filler expression's filler is element dependent

[Timm Bäder via Phabricator via cfe-commits]

tbaeder created this revision.
tbaeder added reviewers: aaron.ballman, erichkeane.
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This is about the problem described in https://discourse.llvm.org/t/apvalue-lifetime-problem-when-evaluating-constant-expressions/64002/5

The (old) condition in this if statement is meant to handle initializers that depend on (other) array elements. In this case, the array needs to be expanded before the array filler is evaluated:

  if (NumEltsToInit != NumElts && MaybeElementDependentArrayFiller(FillerExpr))
    NumEltsToInit = NumElts;

in the test case described on Discourse (which is attached in the patch), `MaybeElementDependentArrayFiller()` returns `false` for the outer array but true for the inner array. Since every `InitListExpr` can have an array filler, I believe the function should take that into account.

This fixes https://github.com/llvm/llvm-project/issues/56016


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D131155

Files:
  clang/lib/AST/ExprConstant.cpp
  clang/test/SemaCXX/constexpr-array-init.cpp


Index: clang/test/SemaCXX/constexpr-array-init.cpp
===================================================================
--- /dev/null
+++ clang/test/SemaCXX/constexpr-array-init.cpp
@@ -0,0 +1,19 @@
+// RUN: %clang_cc1 -std=c++20 -verify %s
+
+struct Foo {
+  int a;
+  constexpr Foo()
+      : a(get_int()) {
+  }
+
+  constexpr int get_int() const {
+    return 5;
+  }
+};
+
+static constexpr Foo bar[2][1] = {
+    {{}},
+};
+static_assert(bar[0][0].a == 5);
+static_assert(bar[1][0].a == 5);
+
Index: clang/lib/AST/ExprConstant.cpp
===================================================================
--- clang/lib/AST/ExprConstant.cpp
+++ clang/lib/AST/ExprConstant.cpp
@@ -10695,6 +10695,11 @@
       if (MaybeElementDependentArrayFiller(ILE->getInit(I)))
         return true;
     }
+
+    if (ILE->hasArrayFiller() &&
+        MaybeElementDependentArrayFiller(ILE->getArrayFiller()))
+      return true;
+
     return false;
   }
   return true;


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