https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103641
Roger Sayle <roger at nextmovesoftware dot com> changed:
What |Removed |Added
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CC| |roger at nextmovesoftware dot
com
--- Comment #18 from Roger Sayle <roger at nextmovesoftware dot com> ---
Hm. PR 87256 was much easier to diagnose, as the cost of multiplication on
hppa64 was 20-30 ALU instructions, so a single pathological multiplier would
combinatorially challenge synth_mult. The new costs on AArch64 have a vector
multiplication cost of 4, which is very reasonable. But I did see somewhere in
Andre's patch that had an ALU cost of COSTS_N_INSNS(0), which would fool
synth_mult that it's allowed/beneficial to use an infinite number of ALU
instructions to avoid a single multiplication. Likewise, the very cheap (free)
shifts on ARM. But this is just guess work; a reduced testcase that exhibits
the problem would be helpful.
