071af74db6
When combine splits a three-insn combination into two instructions it can reuse i2dest for the temporary result of the first new instruction. However all information it has in reg_stat about that register will be stale. This results in the simplify_gen_binary calls in change_zero_ext using out-of-date information, which makes it think one of the ANDs generated there always results in 0, and it doesn't get better from there. This can also happen if a splitter in the MD uses nonzero_bits (for example). I tried to make the splitting code in combine save and restore the i2dest reg_stat info, but that causes one of the acats tests to fail. This whole reg_stat thing needs an overhaul, and/or we shouldn't reuse i2dest for unrelated purposes when splitting. This patch changes change_zero_ext to do the expected simplifications itself and not call simplify_gen_*. PR rtl-optimization/78232 * combine.c (try_combine): Add a big comment about why reusing i2dest is undesirable. (change_zero_ext): Do not call simplify_gen_binary, do the simplifications manually. From-SVN: r242059 |
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