On 03/23/2015 09:07 AM, Jakub Jelinek wrote:
Hi!
As expand_set_or_movmem_prologue_epilogue_by_misaligned_moves uses
src = src - (adjusted_dest - dest)
without proper REG_POINTER flags the aliasing code is very easily confused
on what is really a pointer and what is not - as REG_POINTER was used
after forwprop only on dest, but not on anything else, aliasing code thinks
that the memcpy reads dest based memory, when it really reads src based
memory (in the testcase frame pointer based in the end, but CSE did not see
it through).
Fixed by marking pseudos that must hold pointers with REG_POINTER during
the expansion. Bootstrapped/regtested on x86_64-linux and i686-linux, ok
for trunk?
FWIW, you have to be very careful depending on REG_POINTER. I believe
Ada can still set REG_POINTER on things that are not pointers (via
virtual origins) and cross jumping can cause problems too where one arm
has x + y with X as the pointer and the other arm has x + y with Y as
the pointer.
But yes, in general, if we're marking things that must be pointers with
REG_POINTER, that is a good thing.
jeff
