https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109778
--- Comment #12 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-11 branch has been updated by Jakub Jelinek <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:817d1496e17806bdefab1e0fb06abdf56df58cbd commit r11-10753-g817d1496e17806bdefab1e0fb06abdf56df58cbd Author: Jakub Jelinek <ja...@redhat.com> Date: Tue May 9 12:10:07 2023 +0200 tree-ssa-ccp, wide-int: Fix up handling of [LR]ROTATE_EXPR in bitwise ccp [PR109778] The following testcase is miscompiled, because bitwise ccp2 handles a rotate with a signed type incorrectly. Seems tree-ssa-ccp.cc has the only callers of wi::[lr]rotate with 3 arguments, all other callers just rotate in the right precision and I think work correctly. ccp works with widest_ints and so rotations by the excessive precision certainly don't match what it wants when it sees a rotate in some specific bitsize. Still, if it is unsigned rotate and the widest_int is zero extended from width, the functions perform left shift and logical right shift on the value and then at the end zero extend the result of left shift and uselessly also the result of logical right shift and return | of that. On the testcase we the signed char rrotate by 4 argument is CONSTANT -75 i.e. 0xffffffff....fffffb5 with mask 2. The mask is correctly rotated to 0x20, but because the 8-bit constant is sign extended to 192-bit one, the logical right shift by 4 doesn't yield expected 0xb, but gives 0xfffffffffff....ffffb, and then return wi::zext (left, width) | wi::zext (right, width); where left is 0xfffffff....fb50, so we return 0xfb instead of the expected 0x5b. The following patch fixes that by doing the zero extension in case of the right variable before doing wi::lrshift rather than after it. Also, wi::[lr]rotate widht width < precision always zero extends the result. I'm afraid it can't do better because it doesn't know if it is done for an unsigned or signed type, but the caller in this case knows that very well, so I've done the extension based on sgn in the caller. E.g. 0x5b rotated right (or left) by 4 with width 8 previously gave 0xb5, but sgn == SIGNED in widest_int it should be 0xffffffff....fffb5 instead. 2023-05-09 Jakub Jelinek <ja...@redhat.com> PR tree-optimization/109778 * wide-int.h (wi::lrotate, wi::rrotate): Call wi::lrshift on wi::zext (x, width) rather than x if width != precision, rather than using wi::zext (right, width) after the shift. * tree-ssa-ccp.c (bit_value_binop): Call wi::ext on the results of wi::lrotate or wi::rrotate. * gcc.c-torture/execute/pr109778.c: New test. (cherry picked from commit a8302d2a4669984c7c287d12ef5b37cde6699c80)
