06ac981ffb
As mentioned in the PR, this hunk is guarded with !wi::neg_p (r1val | r1mask, sgn) which means if sgn is UNSIGNED, it is always true, but r1val | r1mask in widest_int is still sign-extended. That means wi::clz (arg) returns 0, wi::get_precision (arg) returns some very large number (WIDE_INT_MAX_PRECISION, on x86_64 576 bits) and width is 64, so we end up with lzcount of -512 where the code afterwards expects a non-negative lzcount. For arg without the sign bit set the code works right, those numbers are zero extended and so wi::clz must return wi::get_precision (arg) - width plus number of leading zero bits within the width precision. The patch fixes it by handling the sign-extension specially, either it could be done through wi::neg_p (arg) check, but lzcount == 0 works identically. 2021-08-31 Jakub Jelinek <jakub@redhat.com> PR tree-optimization/102134 * tree-ssa-ccp.c (bit_value_binop) <case RSHIFT_EXPR>: If sgn is UNSIGNED and r1val | r1mask has MSB set, ensure lzcount doesn't become negative. * gcc.c-torture/execute/pr102134.c: New test. |
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