[cfe-commits] [PATCH] PR12290: introducing overflow builtins

[Xi Wang]

Hi,

The attached patch addresses the comments from Eli Friedman. 
- whitespace nit
- remove useless check
- reject bool type

http://lists.cs.uiuc.edu/pipermail/cfe-dev/2012-May/021687.html

Also rebased on the latest trunk.

You can review the changes at

https://github.com/xiw/clang/compare/builtin-overflow

Thanks for reviewing.

- xi
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On Apr 17, 2012, at 12:28 PM, Xi Wang wrote:

> The attached patch makes two changes.
> 
> - Enabled 128-bit integer operation in overflow builtins.
> 
> - Rebased on the latest trunk.
> 
> Please review!  Thanks.
> 
> - xi
> <overflow.patch>
> On Apr 4, 2012, at 8:18 PM, Xi Wang wrote:
> 
>> Hi,
>> 
>> Attached is a patch that adds arithmetic with overflow builtins to Clang.  Please review.  Thanks.
>> 
>> Arithmetic with overflow builtins are used to perform arithmetic operations with overflow detection.
>> 
>> Syntax:
>> 
>> bool __builtin_add_with_overflow(type *ptr, type a, type b);
>> bool __builtin_sub_with_overflow(type *ptr, type a, type b);
>> bool __builtin_mul_with_overflow(type *ptr, type a, type b);
>> 
>> Example of Use:
>> 
>> void *malloc_array(size_t n, size_t size) {
>> size_t bytes;
>> if (__builtin_mul_with_overflow(&bytes, n, size))
>>   return NULL;
>> return malloc(bytes);
>> }
>> 
>> Description:
>> 
>> __builtin_op_with_overflow(ptr, a, b) stores the result of a op b in ptr, and returns true if an overflow occurred during the arithmetic operation. Note that type is inferred from *ptr. These builtins help developers write more efficient and correct code by avoiding ad hoc overflow checks.
>> 
>> Query for this feature with __has_builtin(__builtin_op_with_overflow).
>> 
>> - xi
>