Fix array compound literal parsing #309

lorettayao · 2025-10-06T13:22:56Z

Summary
Fix a segfault when evaluating array compound literals like (int[]){1,2,3,4,5} in expression context. The literal now yields the temporary array’s address (via decay) instead of collapsing to a single element, so indexing and reads work correctly.

Motivation
Previously, code like the snippet below crashed because the array literal was reduced to a scalar and later treated as a pointer.

Reproduction (manual)

#include <stdio.h>

int main(void) {
    int *a = (int[]){1,2,3,4,5};   // used to crash later
    printf("Testing basic array compound literal:\n");
    for (int i = 0; i < 5; i++)
        printf("  a[%d] = %d\n", i, a[i]);

    int sum = a[0] + a[4];
    printf("Sum = %d (expect 6)\n", sum);
    return 0;
}

Before: segfault
After: prints a[0..4] and Sum = 6 as expected

Approach (high level)

Ensure (type[]){…} produces a real temporary array object and the expression value decays to its address.
Only collapse to a scalar when a scalar is actually required by context.
No changes to struct compound literals or plain scalars.

Scope

This PR addresses the array side of Fix compound literals to capture all field values, not just first #299 sufficient to eliminate the segfault in basic use.
Struct compound literals and broader initializer behaviors are intentionally out of scope here.

Tests

No test files are added in this PR. The manual snippet above demonstrates the fix.

Compatibility

Restores standard pointer semantics for array compound literals.
No behavioral changes for structs or scalars.

Issue

Partially addresses Fix compound literals to capture all field values, not just first #299 (array compound literals).

Summary by cubic

Fix parsing of array compound literals so they allocate a temporary array and decay to its address, preserving pointer semantics and preventing segfaults.

Bug Fixes
- Eliminates crashes when using (int[]){...} in expressions, assignments, and parameter passing.
- Correct behavior across binary ops, ternary results, and function-call arguments.
- Addresses Fix compound literals to capture all field values, not just first #299.
Refactors
- Added parse_array_compound_literal and scalarize_array_literal to centralize handling; scalarize only when a scalar is required.
- Emits element writes and counts initializers; tracks brace consumption to avoid double reads.
- Struct and scalar compound literals remain unchanged.

Implement proper array compound literal handling that emits element writes, counts initializers, and returns the temporary array pointer instead of collapsing to the first element. This restores correct pointer semantics and avoids discarding array literals during parsing. Struct and scalar compound literals are unchanged. The parser now tracks whether the closing brace was already consumed by the array helper to prevent double reads.

Introduce helpers to centralize array-literal scalar decay. Temporary array compound literals are detected and converted to a scalar only when a scalar is actually required; otherwise the expression yields the temporary array’s address, preserving pointer semantics. Update binary ops, direct/compound assignments, function-call arguments, and ternary results to use the unified helper instead of ad-hoc collapsing. This fixes cases where array literals were reduced to their first element in pointer contexts, while keeping struct and plain scalar behavior unchanged. Addresses sysprog21#299 (array compound literals).

cubic-dev-ai

2 issues found across 1 file

Prompt for AI agents (all 2 issues)


Understand the root cause of the following 2 issues and fix them.


<file name="src/parser.c">

<violation number="1" location="src/parser.c:1653">
Passing an array compound literal to a variadic function now yields the first element value instead of the temporary array’s address, so variadic calls like `printf(&quot;%p&quot;, (int[]){1,2});` receive an integer instead of a pointer.</violation>

<violation number="2" location="src/parser.c:2901">
Array compound literals are scalarized before binary pointer arithmetic; e.g. `(int[]){1,2} + 1` now produces the integer `2` instead of a pointer to the second element.</violation>
</file>

Since this is your first cubic review, here's how it works:

cubic automatically reviews your code and comments on bugs and improvements
Teach cubic by replying to its comments. cubic learns from your replies and gets better over time
Ask questions if you need clarification on any suggestion

_{React with 👍 or 👎 to teach cubic. Mention @cubic-dev-ai to give feedback, ask questions, or re-run the review.}

src/parser.c

cubic-dev-ai · 2025-10-06T13:31:45Z

src/parser.c

+                    param = scalarize_array_literal(parent, bb, param,
+                                                    target->type);
+            } else if (func->va_args) {
+                param = scalarize_array_literal(parent, bb, param, TY_int);


Passing an array compound literal to a variadic function now yields the first element value instead of the temporary array’s address, so variadic calls like printf("%p", (int[]){1,2}); receive an integer instead of a pointer.

Prompt for AI agents

Address the following comment on src/parser.c at line 1653: <comment>Passing an array compound literal to a variadic function now yields the first element value instead of the temporary array’s address, so variadic calls like `printf("%p", (int[]){1,2});` receive an integer instead of a pointer.</comment> <file context> @@ -1575,7 +1643,16 @@ void read_func_parameters(func_t *func, block_t *parent, basic_block_t **bb) + param = scalarize_array_literal(parent, bb, param, + target->type); + } else if (func->va_args) { + param = scalarize_array_literal(parent, bb, param, TY_int); + } + } </file context>

✅ Addressed in d6b9fbf

jserv · 2025-10-06T14:02:23Z

src/parser.c

+    }
+    lex_expect(T_close_curly);
+    var->array_size = count;
+}


Add a new blank line.

DrXiao

Add some test cases to the test suite for validation.

jserv

Don't use static qualifier since shecc does not support. Check 'COMPLIANCE.md' carefully.

src/parser.c

jserv · 2025-10-06T14:07:42Z

You MUST ensure bootstrapping is fully functional before submitting pull requests.

visitorckw · 2025-10-06T14:34:14Z

IIUC, compound literals are a feature supported only since C99, and the shecc README mentions from the very beginning that this project aims to support ANSI C. Therefore, IMO, this at least does not "fix" anything.

DrXiao · 2025-10-06T14:49:42Z

IIUC, compound literals are a feature supported only since C99, and the shecc README mentions from the very beginning that this project aims to support ANSI C. Therefore, IMO, this at least does not "fix" anything.

As far as I know, shecc is planned to fully support the C99 standard, so I think the term "fix" is acceptable.

visitorckw · 2025-10-06T14:53:37Z

Fine, but since we haven't claimed to fully support C99 and, IIUC, array compound literals were never supported before, this seems more like supporting a new feature to me, rather than fixing an existing problem.

DrXiao · 2025-10-06T15:10:25Z

In fact, shecc has ability to handle array compound literals, but it only captures the first element (#299).

Therefore, this pull request specifically aims to fix it.

visitorckw · 2025-10-06T15:21:20Z

In fact, shecc has ability to handle array compound literals, but it only captures the first element (#299).

Therefore, this pull request specifically aims to fix it.

Thanks, that resolves my doubt.
However, should we also mention the issue in the first commit?

src/parser.c

jserv

Don't add tests/array_ptr.c. Instead, consolidate tests/driver.sh.

visitorckw

Please rebase your branch to keep the git history clean.
Commits that fix problems introduced within the same pull request should be avoided.

jserv · 2025-10-08T13:20:34Z

src/parser.c

+
+    add_insn(parent, *bb, OP_read, scalar, array_var, NULL, elem_size, NULL);
+    return scalar;
+}


Add a line break.

lorettayao added 2 commits October 6, 2025 19:51

cubic-dev-ai bot reviewed Oct 6, 2025

View reviewed changes

jserv reviewed Oct 6, 2025

View reviewed changes

DrXiao suggested changes Oct 6, 2025

View reviewed changes

jserv requested changes Oct 6, 2025

View reviewed changes

jserv reviewed Oct 6, 2025

View reviewed changes

src/parser.c Outdated Show resolved Hide resolved

Fix formatting, add testcase, remove static

b44dc57

lorettayao added 3 commits October 8, 2025 15:18

Fix misleading function naming

1f7bed4

Fix data format according to warnings

d6b9fbf

add: test case for array compound literals

272c912

jserv reviewed Oct 8, 2025

View reviewed changes

src/parser.c Outdated Show resolved Hide resolved

jserv requested changes Oct 8, 2025

View reviewed changes

Change function name and remove test case

accfedf

visitorckw suggested changes Oct 8, 2025

View reviewed changes

jserv reviewed Oct 8, 2025

View reviewed changes

Update driver snapshots after decay tests

fefbeee

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

Fix array compound literal parsing #309

Fix array compound literal parsing #309

lorettayao commented Oct 6, 2025 •

edited by jserv

Loading

Uh oh!

cubic-dev-ai bot left a comment

Uh oh!

Uh oh!

cubic-dev-ai bot Oct 6, 2025 •

edited

Loading

Uh oh!

jserv Oct 6, 2025

Uh oh!

DrXiao left a comment

Uh oh!

jserv left a comment

Uh oh!

Uh oh!

jserv commented Oct 6, 2025

Uh oh!

visitorckw commented Oct 6, 2025

Uh oh!

DrXiao commented Oct 6, 2025

Uh oh!

visitorckw commented Oct 6, 2025

Uh oh!

DrXiao commented Oct 6, 2025

Uh oh!

visitorckw commented Oct 6, 2025

Uh oh!

Uh oh!

jserv left a comment

Uh oh!

visitorckw left a comment

Uh oh!

jserv Oct 8, 2025

Uh oh!

Uh oh!

Fix array compound literal parsing #309

Are you sure you want to change the base?

Fix array compound literal parsing #309

Conversation

lorettayao commented Oct 6, 2025 • edited by jserv Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Summary by cubic

Uh oh!

cubic-dev-ai bot left a comment

Choose a reason for hiding this comment

Uh oh!

Uh oh!

cubic-dev-ai bot Oct 6, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

jserv Oct 6, 2025

Choose a reason for hiding this comment

Uh oh!

DrXiao left a comment

Choose a reason for hiding this comment

Uh oh!

jserv left a comment

Choose a reason for hiding this comment

Uh oh!

Uh oh!

jserv commented Oct 6, 2025

Uh oh!

visitorckw commented Oct 6, 2025

Uh oh!

DrXiao commented Oct 6, 2025

Uh oh!

visitorckw commented Oct 6, 2025

Uh oh!

DrXiao commented Oct 6, 2025

Uh oh!

visitorckw commented Oct 6, 2025

Uh oh!

Uh oh!

jserv left a comment

Choose a reason for hiding this comment

Uh oh!

visitorckw left a comment

Choose a reason for hiding this comment

Uh oh!

jserv Oct 8, 2025

Choose a reason for hiding this comment

Uh oh!

Uh oh!

lorettayao commented Oct 6, 2025 •

edited by jserv

Loading

cubic-dev-ai bot Oct 6, 2025 •

edited

Loading