[clang] c6bb89f - [clang] Fix assertion failure when initializing union with FAM (#77298)

[via cfe-commits]

Author: Nikita Popov
Date: 2024-01-09T09:18:07+01:00
New Revision: c6bb89f308c6715edf3f35fb7c6257713ecfc614

URL: https://github.com/llvm/llvm-project/commit/c6bb89f308c6715edf3f35fb7c6257713ecfc614
DIFF: https://github.com/llvm/llvm-project/commit/c6bb89f308c6715edf3f35fb7c6257713ecfc614.diff

LOG: [clang] Fix assertion failure when initializing union with FAM (#77298)

When initializing a union that constrain a struct with a flexible array
member, and the initializer list is empty, we currently trigger an
assertion failure. This happens because getFlexibleArrayInitChars()
assumes that the initializer list is non-empty.

Fixes https://github.com/llvm/llvm-project/issues/77085.

Added: 
    

Modified: 
    clang/docs/ReleaseNotes.rst
    clang/lib/AST/Decl.cpp
    clang/test/CodeGen/flexible-array-init.c

Removed: 
    


################################################################################
diff  --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 803eb2f7c74cf6..980be4fe0ef741 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -696,6 +696,9 @@ Bug Fixes in This Version
 - Clang now accepts recursive non-dependent calls to functions with deduced
   return type.
   Fixes (`#71015 <https://github.com/llvm/llvm-project/issues/71015>`_)
+- Fix assertion failure when initializing union containing struct with
+  flexible array member using empty initializer list.
+  Fixes (`#77085 <https://github.com/llvm/llvm-project/issues/77085>`_)
 
 
 Bug Fixes to Compiler Builtins

diff  --git a/clang/lib/AST/Decl.cpp b/clang/lib/AST/Decl.cpp
index 12e0a6faa4c33d..e1440e5183a4e6 100644
--- a/clang/lib/AST/Decl.cpp
+++ b/clang/lib/AST/Decl.cpp
@@ -2835,7 +2835,7 @@ CharUnits VarDecl::getFlexibleArrayInitChars(const ASTContext &Ctx) const {
   if (!Ty || !Ty->getDecl()->hasFlexibleArrayMember())
     return CharUnits::Zero();
   auto *List = dyn_cast<InitListExpr>(getInit()->IgnoreParens());
-  if (!List)
+  if (!List || List->getNumInits() == 0)
     return CharUnits::Zero();
   const Expr *FlexibleInit = List->getInit(List->getNumInits() - 1);
   auto InitTy = Ctx.getAsConstantArrayType(FlexibleInit->getType());

diff  --git a/clang/test/CodeGen/flexible-array-init.c b/clang/test/CodeGen/flexible-array-init.c
index b2cf959f7e1220..bae926da5feb07 100644
--- a/clang/test/CodeGen/flexible-array-init.c
+++ b/clang/test/CodeGen/flexible-array-init.c
@@ -20,3 +20,11 @@ struct __attribute((packed, aligned(4))) { char a; int x; char z[]; } e = { 1, 2
 
 struct { int x; char y[]; } f = { 1, { 13, 15 } };
 // CHECK: @f ={{.*}} global <{ i32, [2 x i8] }> <{ i32 1, [2 x i8] c"\0D\0F" }>
+
+union {
+  struct {
+    int a;
+    char b[];
+  } x;
+} in_union = {};
+// CHECK: @in_union ={{.*}} global %union.anon zeroinitializer