On 04/21/2015 11:33 AM, Kyrill Tkachov wrote:
On 21/04/15 15:09, Jeff Law wrote:
On 04/21/2015 02:30 AM, Kyrill Tkachov wrote:
From reading config/stormy16/stormy-abi it seems to me that we don't
pass arguments partially in stormy16, so this code would never be called
there. That leaves pa as the potential problematic target.
I don't suppose there's an easy way to test on pa? My checkout of
binutils
doesn't seem to include a sim target for it.
No simulator, no machines in the testfarm, the box I had access to via
parisc-linux.org seems dead and my ancient PA overheats well before a
bootstrap could complete. I often regret knowing about the backwards
way many things were done on the PA because it makes me think about
cases that only matter on dead architectures.
So what should be the action plan here? I can't add an assert on
positive result as a negative result is valid.
We want to catch the case where this would cause trouble on
pa, or change the patch until we're confident that it's fine
for pa.
That being said, reading the documentation of STACK_GROWS_UPWARD
and ARGS_GROW_DOWNWARD I'm having a hard time visualising a case
where this would cause trouble on pa.
Is the problem that in the function:
+/* Add SIZE to X and check whether it's greater than Y.
+ If it is, return the constant amount by which it's greater or smaller.
+ If the two are not statically comparable (for example, X and Y contain
+ different registers) return -1. This is used in expand_push_insn to
+ figure out if reading SIZE bytes from location X will end up reading
from
+ location Y. */
+static int
+memory_load_overlap (rtx x, rtx y, HOST_WIDE_INT size)
+{
+ rtx tmp = plus_constant (Pmode, x, size);
+ rtx sub = simplify_gen_binary (MINUS, Pmode, tmp, y);
+
+ if (!CONST_INT_P (sub))
+ return -1;
+
+ return INTVAL (sub);
+}
for ARGS_GROW_DOWNWARD we would be reading 'backwards' from x,
so the function should something like the following?
So I had to go back and compile some simple examples.
References to outgoing arguments will be SP relative. References to the
incoming arguments will be ARGP relative. And that brings me to the
another issue. Isn't X in this context the incoming argument slot and
the destination an outgoing argument slot?
If so, the approach of memory_load_overlap simply won't work on a target
with calling conventions like the PA. And you might really want to
consider punting for these kind of calling conventions
If you hadn't already done the work, I'd suggest punting for any case
where we have args partially in regs and partially in memory :-)
More thoughts when I can get an hour or two to remind myself how all
this stuff works on the PA.
I will note that testing on the PA is unlikely to show anything simply
because it uses 8 parameter passing registers. So it's rare to pass
anything in memory at all. Even rarer to have something partially in
memory and partially in registers.
Jeff
