More C changes

content/c-vla.md

@@ -21,15 +21,6 @@ only at runtime, useful for algorithms where the size depends on function parame
 ```c
 #include <stdio.h>
 
-void print_matrix(int rows, int cols, int matrix[rows][cols]) {
-    for (int i = 0; i < rows; i++) {
-        for (int j = 0; j < cols; j++) {
-            printf("%3d ", matrix[i][j]);
-        }
-        printf("\n");
-    }
-}
-
 int main(void) {
     int n = 3;
     int arr[n];  // VLA with runtime size
@@ -41,8 +32,5 @@ int main(void) {
     for (int i = 0; i < n; i++)
         printf("%d ", arr[i]);
     printf("\n");
-
-    int matrix[2][3] = {{1, 2, 3}, {4, 5, 6}};
-    print_matrix(2, 3, matrix);
 }
 ```

content/c-vm-types.md

@@ -0,0 +1,36 @@
+---
+execute: true
+show_assembly: true
+flags: "-std=c99"
+---
+
+## What It Does
+
+Variably-modified types are types of variable-length arrays or types derived from VLAs,
+e.g. pointers to VLAs or multi-dimensional arrays types where some dimension is variable.
+
+## Why It Matters
+
+Variably-modified types encode the number of elements of arrays in their type.  This
+allows convenient indexing into multi-dimenional arrays, recovery of the number of
+elements from the type, and enables improved static analysis and automatic bounds checking.
+
+## Example
+
+```c
+#include <stdio.h>
+
+void print_matrix(int rows, int cols, int matrix[rows][cols]) {
+    for (int i = 0; i < rows; i++) {
+        for (int j = 0; j < cols; j++) {
+            printf("%3d ", matrix[i][j]);
+        }
+        printf("\n");
+    }
+}
+
+int main(void) {
+    int matrix[2][3] = {{1, 2, 3}, {4, 5, 6}};
+    print_matrix(2, 3, matrix);
+}
+```

features_c23.yaml

@@ -73,9 +73,13 @@ features:
     paper: N2508
     support:
       - GCC 11
-      - Clang 16
+      - Clang 16 (partial)
+      - Clang 18
       - MSVC (partial)
       - Xcode 15
+    hints:
+      - target: Clang 16
+        msg: "Only labels at the end of a block are supported"
   - desc: "[Binary integer constants](https://en.cppreference.com/w/c/language/integer_constant.html)"
     paper: N2549
     content: c-binary-literals.md
@@ -186,6 +190,13 @@ features:
       - GCC 14
       - Clang 15
       - Xcode 16.1
+  - desc: "Require support for variably modified types"
+    paper: N2778
+    support:
+      - GCC
+      - Clang
+      - Xcode
+      - TinyCC 0.9.28
   - desc: "`__has_include` in preprocessor conditionals"
     paper: N2799
     support:
@@ -210,12 +221,12 @@ features:
     paper: N2900
     content: c-empty-init.md
     support:
-      - GCC 13 (partial)
+      - GCC 13
       - Clang (partial)
       - Xcode (partial)
     hints:
       - target: GCC 13
-        msg: "Supported as an extension. Missing support for scalars and variable-length arrays (VLAs)."
+        msg: "Partially supported as an extension before."
       - target: Clang
         msg: "Supported as an extension. Missing support for scalars and variable-length arrays (VLAs)."
       - target: Xcode
@@ -326,3 +337,10 @@ features:
       - GCC 13
       - Clang 16 (partial)
       - Xcode 16.1
+  - desc: "Partial program correctness"
+    paper: N3128
+    support:
+      - GCC (partial)
+    hints:
+      - target: GCC
+        msg: "Not guaranteed for volatile accesses"

features_c2y.yaml

@@ -269,9 +269,6 @@ features:
       - GCC 16
       - Xcode 16.4
 
-  - desc: "`auto` as placeholder type for parameters"
-    paper: N3472
-
   - desc: "Slay Some Earthly Demons XIII"
     paper: N3478
     support:
@@ -313,8 +310,10 @@ features:
   - desc: "Member access of an incomplete object"
     paper: N3532
     support:
+      - GCC
+      - MSVC
       - Clang
-      - Xcode 16.4
+      - Xcode
 
   - desc: "Chasing Ghosts I: constant expressions"
     paper: N3558
@@ -339,6 +338,7 @@ features:
   - desc: "Earthly Demon XV: Definition of Main"
     paper: N3623
     support:
+      - GCC
       - Clang
       - Xcode ?
 

features_c99.yaml

@@ -68,11 +68,14 @@ features:
       - Clang
       - Xcode 14
       - TinyCC
-  - desc: "Variably-modified (VM) types"
-    paper: N2778
+  - desc: "[Variably-modified](https://en.cppreference.com/w/c/language/array.html#Variable-length_arrays) (VM) types"
+    paper: N683
+    content: c-vm-types.md
     support:
+      - GCC
       - Clang
       - Xcode
+      - TinyCC 0.9.28
   - desc: "Designated initializers"
     paper: N494
     content: c-designated-init.md