[clang] 2ae0905 - [C23] Claim we do not conform to N2819

[Aaron Ballman via cfe-commits]

Author: Aaron Ballman
Date: 2024-06-24T15:09:20-04:00
New Revision: 2ae09052477e1a966afbc5482d88585f95694c53

URL: https://github.com/llvm/llvm-project/commit/2ae09052477e1a966afbc5482d88585f95694c53
DIFF: https://github.com/llvm/llvm-project/commit/2ae09052477e1a966afbc5482d88585f95694c53.diff

LOG: [C23] Claim we do not conform to N2819

This paper clarified the lifetime of compound literal objects in odd
scopes, such as use at function prototype scope.

We do not currently implement this paper, as the new test demonstrates.

Added: 
    clang/test/C/C2x/n2819.c

Modified: 
    clang/www/c_status.html

Removed: 
    


################################################################################
diff  --git a/clang/test/C/C2x/n2819.c b/clang/test/C/C2x/n2819.c
new file mode 100644
index 0000000000000..c428fbba80245
--- /dev/null
+++ b/clang/test/C/C2x/n2819.c
@@ -0,0 +1,57 @@
+// NOTE: Assertions have been autogenerated by utils/update_cc_test_checks.py UTC_ARGS: --version 3
+// RUN: %clang_cc1 -triple=x86_64 -emit-llvm -o - -std=c23 %s | FileCheck %s
+
+/* WG14 N2819: No
+ * Disambiguate the storage class of some compound literals
+ */
+
+int *escaped;
+// CHECK-LABEL: define dso_local i32 @f(
+// CHECK-SAME: ptr noundef [[PTR:%.*]]) #[[ATTR0:[0-9]+]] {
+// CHECK-NEXT:  entry:
+// CHECK-NEXT:    [[PTR_ADDR:%.*]] = alloca ptr, align 8
+// CHECK-NEXT:    store ptr [[PTR]], ptr [[PTR_ADDR]], align 8
+// CHECK-NEXT:    [[TMP0:%.*]] = load ptr, ptr [[PTR_ADDR]], align 8
+// CHECK-NEXT:    store ptr [[TMP0]], ptr @escaped, align 8
+// CHECK-NEXT:    ret i32 1
+//
+int f(int *ptr) { escaped = ptr; return 1; }
+
+// CHECK-LABEL: define dso_local i32 @g(
+// CHECK-SAME: ptr noundef [[PARA:%.*]]) #[[ATTR0]] {
+// CHECK-NEXT:  entry:
+// CHECK-NEXT:    [[PARA_ADDR:%.*]] = alloca ptr, align 8
+// CHECK-NEXT:    store ptr [[PARA]], ptr [[PARA_ADDR]], align 8
+// CHECK-NEXT:    [[CALL:%.*]] = call i32 @f(ptr noundef @.compoundliteral)
+// CHECK-NEXT:    [[TMP0:%.*]] = zext i32 [[CALL]] to i64
+// CHECK-NEXT:    ret i32 0
+//
+// FIXME: notice the we are using the global .compoundliteral object, not
+// allocating a new object on each call to g(). That's what was clarified by
+// N2819.
+int g(char *para [f(( int [27]) { 0 })]) {
+  return 0;
+}
+
+// CHECK-LABEL: define dso_local i32 @main(
+// CHECK-SAME: ) #[[ATTR0]] {
+// CHECK-NEXT:  entry:
+// CHECK-NEXT:    [[RETVAL:%.*]] = alloca i32, align 4
+// CHECK-NEXT:    store i32 0, ptr [[RETVAL]], align 4
+// CHECK-NEXT:    [[CALL:%.*]] = call i32 @g(ptr noundef null)
+// CHECK-NEXT:    [[TMP0:%.*]] = load ptr, ptr @escaped, align 8
+// CHECK-NEXT:    store i32 12, ptr [[TMP0]], align 4
+// CHECK-NEXT:    [[TMP1:%.*]] = load ptr, ptr @escaped, align 8
+// CHECK-NEXT:    [[TMP2:%.*]] = load i32, ptr [[TMP1]], align 4
+// CHECK-NEXT:    ret i32 [[TMP2]]
+//
+int main() {
+  // Sets 'escaped' to the address of the array created by the compound literal.
+  g(nullptr);
+
+  // The lifetime of that object should have ended when g() returned, so this
+  // should be a use-after-free.
+  *escaped = 12;
+  return *escaped;
+}
+

diff  --git a/clang/www/c_status.html b/clang/www/c_status.html
index 434c9e20011d4..25656c0304da1 100644
--- a/clang/www/c_status.html
+++ b/clang/www/c_status.html
@@ -1025,7 +1025,7 @@ <h2 id="c2x">C23 implementation status</h2>
     <tr>
       <td>Disambiguate the storage class of some compound literals</td>
       <td><a href="https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2819.pdf">N2819</a></td>
-      <td class="unknown" align="center">Unknown</td>
+      <td class="none" align="center">No</td>
     </tr>
     <tr>
       <td>Add annotations for unreachable control flow v2</td>