https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112611
--- Comment #3 from Jiahao Xu <xujiahao at loongson dot cn> --- (In reply to Xi Ruoyao from comment #2) > (In reply to Jiahao Xu from comment #1) > > Due to some issues with the implementation of the [x]vshuf instruction in > > LA464, there is a problem where, when the index value in the register is > > greater than or equal to 64, it fails to perform modulo operation to obtain > > a new index for selecting the corresponding element. Instead, it directly > > writes a 0 to the destination register. LA664 has fixed this issue. > > > > The expected results in these two files are not the correct results, but > > rather the results obtained directly using the [x]vshuf instruction on > > la464. This is why they fail on LA664. Now, there are two possible > > solutions. One is to delete these two problematic test cases, as you > > suggested. The other solution is to modify the expected results to the > > correct ones and only test these two files on LA664. We are currently > > considering which option to choose. > > Maybe just rewriting the results to match LA664, and invoke CPUCFG to skip > these tests for any other implementations? > > In the future we better assign a CPUCFG bit to indicate this. We now consider it as undefined behavior rather than a bug for [x]vshuf instructions. In vec_perm pattern, we use vector logical AND instructions to perform modulo operations in order to correctly use the [x]vshuf instructions. Therefore, we have decided to rewrite the two tests and ensure that the index values in the selector do not exceed 64.
