Hi,
I looked into PR43491 a while and found in this case the gimple
generated before pre
is like:
reg.0_12 = reg
...
c()
reg.0_1 = reg
D.xxx = MEM[reg.0_1 + 8B]
The pre pass transforms it into:
reg.0_12 = reg
...
c()
reg.0_1 = reg.0_12
D.xxx = MEM[reg.0_1 + 8B]
>From now on, following passes(like copy_prop) can not transform it back and
resulting in an additional mov instruction as the bug reported.
The flow is like:
1, when rewriting gimple into ssa, reg is treated as a memory use;
2, seems pre noticed that reg is const and replace reg with reg.0_12,
by this pre thinks it has eliminated an additional memory load operation;
3, following passes do not transform it back either because reg is treated
as mem use or the const attribute is ignored.
I think pre does the right thing given the information it knows, so wondering
at which pass thing starts going wrong and how could this issue be handled?
Thanks very much
--
Best Regards.
