[clang] [clang] Disallow VLA type compound literals (PR #91891)
Jim M. R. Teichgräber via cfe-commits
cfe-commits at lists.llvm.org
Sun May 12 08:49:06 PDT 2024
https://github.com/J-MR-T created https://github.com/llvm/llvm-project/pull/91891
C99-C23 6.5.2.5 says: The type name shall specify an object type or an array of unknown size, but not a variable length array type.
Closes issue #89835 .
I ran `git clang-format`'ed my changes and ran the clang tests, which passed after minor adjustments to the new behavior.
I mostly implemented everything as discussed in #89835, with the exception of [clang/test/C/C2x/n2900_n3011_2.c](https://github.com/llvm/llvm-project/compare/main...J-MR-T:llvm-project:main#diff-aa2b77ff42fcd2f2c02cc456f5023e923d44e5018dd2af7c046ebdcc8cb00a4a): in that file I deleted the part about VLA compound literals, because the file relies on LLVM-IR being emitted by clang, and that wouldn't have fit with the rest of the file. Adding another RUN line and handling this case independently in that file would be an option, but it felt out of place. Of course, I'm still open to doing it that way, or preserving the test another way, if that is preferred.
As I point out [here](https://github.com/llvm/llvm-project/compare/main...J-MR-T:llvm-project:main#diff-3c28567b5e0c77d68f174541a0b77f5a85d093f58b89cd3675ee04a550a44880R7278-R7283), the new behavior leads to a confusing reality brought about by the C23 standard:
```c
int a[size] = {};
```
is valid code, while
```c
int a[size] = (int[size]){};
```
is not. As this seems to be what the standard requests, I implemented it that way for now.
Tagging @Sirraide and @AaronBallman as requested :).
>From 9aab9284fc094d22e12a2ee1217a3bc99e5837b8 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jim=20M=2E=20R=2E=20Teichgr=C3=A4ber?=
<jimmr.teichgraeber at tum.de>
Date: Sun, 12 May 2024 13:33:37 +0200
Subject: [PATCH] [clang] Disallow VLA type compound literals C99-C23 6.5.2.5
says: The type name shall specify an object type or an array of unknown size,
but not a variable length array type Issue:
https://github.com/llvm/llvm-project/issues/89835
---
.../clang/Basic/DiagnosticSemaKinds.td | 2 ++
clang/lib/Sema/SemaExpr.cpp | 19 +++++++++++++------
clang/test/C/C2x/n2900_n3011.c | 8 +++++++-
clang/test/C/C2x/n2900_n3011_2.c | 16 ----------------
clang/test/Sema/compound-literal.c | 15 +++++++++++++--
5 files changed, 35 insertions(+), 25 deletions(-)
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index d6863f90edb6e..008d7b2a29cd9 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -3371,6 +3371,8 @@ def err_field_with_address_space : Error<
"field may not be qualified with an address space">;
def err_compound_literal_with_address_space : Error<
"compound literal in function scope may not be qualified with an address space">;
+def err_compound_literal_with_vla_type : Error<
+ "compound literal has variable-length array type">;
def err_address_space_mismatch_templ_inst : Error<
"conflicting address space qualifiers are provided between types %0 and %1">;
def err_attr_objc_ownership_redundant : Error<
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index c688cb21f2364..e62e3f3285e5d 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -7274,12 +7274,19 @@ Sema::BuildCompoundLiteralExpr(SourceLocation LParenLoc, TypeSourceInfo *TInfo,
// init a VLA in C++ in all cases (such as with non-trivial constructors).
// FIXME: should we allow this construct in C++ when it makes sense to do
// so?
- std::optional<unsigned> NumInits;
- if (const auto *ILE = dyn_cast<InitListExpr>(LiteralExpr))
- NumInits = ILE->getNumInits();
- if ((LangOpts.CPlusPlus || NumInits.value_or(0)) &&
- !tryToFixVariablyModifiedVarType(TInfo, literalType, LParenLoc,
- diag::err_variable_object_no_init))
+ //
+ // But: C99-C23 6.5.2.5 Compound literals constraint 1: The type name
+ // shall specify an object type or an array of unknown size, but not a
+ // variable length array type. This seems odd, as it allows int a[size] =
+ // {}; but forbids int a[size] = (int[size]){}; As this is what the
+ // standard says, this is what's implemented here for C (except for the
+ // extension that permits constant foldable size arrays)
+
+ auto diagID = LangOpts.CPlusPlus
+ ? diag::err_variable_object_no_init
+ : diag::err_compound_literal_with_vla_type;
+ if (!tryToFixVariablyModifiedVarType(TInfo, literalType, LParenLoc,
+ diagID))
return ExprError();
}
} else if (!literalType->isDependentType() &&
diff --git a/clang/test/C/C2x/n2900_n3011.c b/clang/test/C/C2x/n2900_n3011.c
index 4350aa140691b..f0be8b9e41861 100644
--- a/clang/test/C/C2x/n2900_n3011.c
+++ b/clang/test/C/C2x/n2900_n3011.c
@@ -27,8 +27,14 @@ void test(void) {
compat-warning {{use of an empty initializer is incompatible with C standards before C23}}
int vla[i] = {}; // compat-warning {{use of an empty initializer is incompatible with C standards before C23}} \
pedantic-warning {{use of an empty initializer is a C23 extension}}
+ // C99 6.5.2.5 Compound literals constraint 1: The type name shall specify an
+ // object type or an array of unknown size, but not a variable length array
+ // type.
int *compound_literal_vla = (int[i]){}; // compat-warning {{use of an empty initializer is incompatible with C standards before C23}} \
- pedantic-warning {{use of an empty initializer is a C23 extension}}
+ pedantic-warning {{use of an empty initializer is a C23 extension}}\
+ compat-error {{compound literal has variable-length array type}} \
+ pedantic-error {{compound literal has variable-length array type}}\
+
struct T {
int i;
diff --git a/clang/test/C/C2x/n2900_n3011_2.c b/clang/test/C/C2x/n2900_n3011_2.c
index eb15fbf905c86..ab659d636d155 100644
--- a/clang/test/C/C2x/n2900_n3011_2.c
+++ b/clang/test/C/C2x/n2900_n3011_2.c
@@ -76,22 +76,6 @@ void test_zero_size_vla() {
// CHECK-NEXT: call void @llvm.memset.p0.i64(ptr {{.*}} %[[VLA]], i8 0, i64 %[[BYTES_TO_COPY]], i1 false)
}
-void test_compound_literal_vla() {
- int num_elts = 12;
- int *compound_literal_vla = (int[num_elts]){};
- // CHECK: define {{.*}} void @test_compound_literal_vla
- // CHECK-NEXT: entry:
- // CHECK-NEXT: %[[NUM_ELTS_PTR:.+]] = alloca i32
- // CHECK-NEXT: %[[COMP_LIT_VLA:.+]] = alloca ptr
- // CHECK-NEXT: %[[COMP_LIT:.+]] = alloca i32
- // CHECK-NEXT: store i32 12, ptr %[[NUM_ELTS_PTR]]
- // CHECK-NEXT: %[[NUM_ELTS:.+]] = load i32, ptr %[[NUM_ELTS_PTR]]
- // CHECK-NEXT: %[[NUM_ELTS_EXT:.+]] = zext i32 %[[NUM_ELTS]] to i64
- // CHECK-NEXT: %[[BYTES_TO_COPY:.+]] = mul nuw i64 %[[NUM_ELTS_EXT]], 4
- // CHECK-NEXT: call void @llvm.memset.p0.i64(ptr {{.*}} %[[COMP_LIT]], i8 0, i64 %[[BYTES_TO_COPY]], i1 false)
- // CHECK-NEXT: store ptr %[[COMP_LIT]], ptr %[[COMP_LIT_VLA]]
-}
-
void test_nested_structs() {
struct T t1 = { 1, {} };
struct T t2 = { 1, { 2, {} } };
diff --git a/clang/test/Sema/compound-literal.c b/clang/test/Sema/compound-literal.c
index a64b6f9e5dfa4..b845ff317225e 100644
--- a/clang/test/Sema/compound-literal.c
+++ b/clang/test/Sema/compound-literal.c
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -fsyntax-only -verify -fblocks -pedantic %s
+// RUN: %clang_cc1 -fsyntax-only -verify -fblocks -pedantic -Wno-comment %s
// REQUIRES: LP64
struct foo { int a, b; };
@@ -29,7 +29,7 @@ int main(int argc, char **argv) {
struct Incomplete; // expected-note{{forward declaration of 'struct Incomplete'}}
struct Incomplete* I1 = &(struct Incomplete){1, 2, 3}; // expected-error {{variable has incomplete type}}
void IncompleteFunc(unsigned x) {
- struct Incomplete* I2 = (struct foo[x]){1, 2, 3}; // expected-error {{variable-sized object may not be initialized}}
+ struct Incomplete* I2 = (struct foo[x]){1, 2, 3}; // expected-error {{compound literal has variable-length array type}}
(void){1,2,3}; // expected-error {{variable has incomplete type}}
(void(void)) { 0 }; // expected-error{{illegal initializer type 'void (void)'}}
}
@@ -42,3 +42,14 @@ int (^block)(int) = ^(int i) {
int *array = (int[]) {i, i + 2, i + 4};
return array[i];
};
+
+// C99 6.5.2.5 Compound literals constraint 1: The type name shall specify an object type or an array of unknown size, but not a variable length array type.
+// So check that VLA type compound literals are rejected (see https://github.com/llvm/llvm-project/issues/89835).
+void vla(int n) {
+ int size = 5;
+ (void)(int[size]){}; // expected-warning {{use of an empty initializer is a C23 extension}} \
+ expected-error {{compound literal has variable-length array type}}
+ (void)(int[size]){1}; // expected-error {{compound literal has variable-length array type}}
+ (void)(int[size]){1,2,3}; // expected-error {{compound literal has variable-length array type}}
+ (void)(int[size]){1,2,3,4,5}; // expected-error {{compound literal has variable-length array type}}
+}
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