[clang] Fix assertion failure when initializing union with FAM #77298
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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 llvm#77085.
llvmbot
added
clang
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@llvm/pr-subscribers-clang Author: Nikita Popov (nikic) ChangesWhen 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. The relevant code is only executed in assertion-enabled builds: https://github.com/llvm/llvm-project/blob/main/clang/lib/CodeGen/CodeGenModule.cpp#L5318-L5324 Fixes #77085. Full diff: https://github.com/llvm/llvm-project/pull/77298.diff 2 Files Affected:
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
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Needs a short release note. |
tbaederr
reviewed
Jan 8, 2024
clang/docs/ReleaseNotes.rst
Outdated
| @@ -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>`) | |||
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I thought the _ was necessary but the documentation builder seems to be happy.
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I've added the underscore to be safe. Wasn't intentional to drop it.
rjmccall
approved these changes
Jan 8, 2024
justinfargnoli
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Jan 28, 2024
…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 llvm#77085.
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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.
The relevant code is only executed in assertion-enabled builds: https://github.com/llvm/llvm-project/blob/main/clang/lib/CodeGen/CodeGenModule.cpp#L5318-L5324
Fixes #77085.