On 7/13/23 09:05, Manolis Tsamis wrote:
In this version I have made f-m-o able to also eliminate constant
moves in addition to the add constant instructions.
This increases the number of simplified/eliminated instructions and is
a good addition for RISC style ISAs where these are more common.
This has led to pr52146.c failing in x86, which I haven't been able to
find a way to fix.
This involves directly writing to a constant address with -mx32
The code
movl $-18874240, %eax
movl $0, (%eax)
is 'optimized' to
movl $0, %eax
movl $0, -18874240(%eax)
Which is actually
movl $0, -18874240
which is wrong per the ticket.
The fix for the ticket involved changes to legitimate_address_p which
f-m-o does call but it doesn't reject due to the existence of (%eax)
which in turn is actually zero.
I believe this is not strictly an f-m-o issue since the pass calls all
the required functions to test whether the newly synthesized memory
instruction is valid.
Any ideas on how to solve this issue is appreciated.
I wonder if costing might be useful here. I would expect the 2nd
sequence is the most costly of the three if address costing models are
reasonably accurate.
Another way would be to look at the length of the memory reference insn.
If it's larger, then it's likely more costly.
That's what I've got off the top of my head.
Jeff
