On 8/4/2026 8:45 PM, liuhongt wrote:
Recognize NEGATE_EXPR, BIT_NOT_EXPR and BIT_XOR_EXPR recurrences.
Fold constant iteration counts and use a conditional for symbolic counts.
Require may_be_zero to be false, since otherwise niter does not
necessarily give the latch count. Keep trapping signed negations
unchanged. This replaces the old invariant bit-operation helper;
idempotent AND and IOR updates are handled by the preceding patch.
gcc/ChangeLog:
PR middle-end/124460
PR middle-end/114502
PR middle-end/112104
PR middle-end/98909
* tree-scalar-evolution.cc
(analyze_and_compute_bitop_with_inv_effect): Remove.
(compute_toggle_loop_value): New function.
(final_value_replacement_loop): Use it.
gcc/testsuite/ChangeLog:
PR middle-end/124460
PR middle-end/114502
PR middle-end/112104
PR middle-end/98909
* gcc.dg/tree-ssa/pr124460-4.c: New test.
* gcc.dg/tree-ssa/pr124460-5.c: Likewise.
* gcc.target/i386/pr105735-1.c: Adjust scan count.
* gcc.target/i386/pr105735-3.c: Likewise.
* gcc.target/i386/pr92080-12.c: Keep the XOR operand variant.
This will need slight readjustment as I think we're better off with
Rachit's patch for the idempotent cases.
It's been eons, but there was a paper, I think from the team at Rice,
"Beyond Induction Variables" or something like that which described a
bunch of these cases. Did you happen to review that paper to see if
there are any other toggle-like cases we should support?
Jeff
