On 07/05/2018 05:54 PM, Martin Sebor wrote:
> GCC folds strlen() calls to empty substrings within arrays
> whose elements are explicitly initialized with NULs but
> fails to do the same for elements that are zeroed out
> implicitly. For example:
>
> const char a[7] = "123\000\000\000";
> int f (void)
> {
> return strlen (a + 5); // folded
> }
>
> but
>
> const char b[7] = "123";
> int g (void)
> {
> return strlen (b + 5); // not folded
> }
>
> This is because the c_getstr() function only considers
> the leading TREE_STRING_LENGTH() number of elements of
> an array and not also the remaining elements up the full
> size of the array the string may be stored in.
>
> The attached patch enhances the function to also consider
> those elements. If there are more elements in the array
> than TREE_STRING_LENGTH() evaluates to they must be all
> NULs because the array is constant and initialized.
>
> Tested along with the patch for PR 77357 on x86_64-linux.
>
> Martin
>
> gcc-86415.diff
>
>
> PR tree-optimization/86415 - strlen() not folded for substrings within
> constant arrays
>
> gcc/ChangeLog:
>
> PR tree-optimization/86415
> * fold-const.c (c_getstr): Handle substrings.
>
> gcc/testsuite/ChangeLog:
>
> PR tree-optimization/86415
> * gcc.dg/strlenopt-48.c: New test.
OK.
jeff
