[Bug target/52055] load of 64-bit pointer reads 64 bits even when only 32 are used

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52055

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 CC|                            |jakub at gcc dot gnu.org

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> 2012-01-31 18:29:33 UTC ---
Combine can already do this kind of change, as can be seen e.g. on
void foo (unsigned long long *p) { asm volatile ("" : : "rm" ((unsigned) *p));
}
where combine shortens the load into SImode load, but on this testcase we don't
attempt to combine it, because cant_combine_insn_p on the insn with subreg says
we shouldn't combine it (the src is a subreg:SI of the reg:DI initialized by
the DImode memory load, but dest is hard register %eax, which has likely
spilled
register class).
So, shell we do this kind of shortening in fwprop instead?  If a MEM load has
all uses subregged to a narrower mode, try to subreg it and adjust the callers?