On 04/28/2015 03:54 AM, Kyrill Tkachov wrote:
On 27/04/15 21:13, Jeff Law wrote:
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
Ok, thanks for the guidance.
How about this? This patch disables sibcall optimisation when
encountering a partial argument when ARGS_GROW_DOWNWARD &&
!STACK_GROWS_DOWNWARD.
Hopefully this shouldn't harm codegen on parisc if, as you say, it's
rare to have
partial arguments anyway on PA due to the large number of argument regs.
I tested this on arm and bootstrapped on x86_64.
I am now going through the process of getting access to a Debian PA
machine to
give it a test there (thanks Dave!)
Ok if testing comes clean?
Thanks,
Kyrill
2015-04-28 Kyrylo Tkachov <kyrylo.tkac...@arm.com>
PR target/65358
* calls.c (expand_call): Cancel sibcall optimisation when encountering
partial argument on targets with ARGS_GROW_DOWNWARD and
!STACK_GROWS_DOWNWARD.
* expr.c (memory_load_overlap): New function.
(emit_push_insn): When pushing partial args to the stack would
clobber the register part load the overlapping part into a pseudo
and put it into the hard reg after pushing.
2015-04-28 Honggyu Kim <hong.gyu....@lge.com>
PR target/65358
* gcc.dg/pr65358.c: New test.
The more I think about this, the more I think it's an ugly can of worms
and maybe we should just disable sibcalls for partial arguments. I
doubt it's a big performance issue in general.
In addition to the argument/stack direction stuff, I've been pondering
the stack/frame/arg pointer issues. Your approach assumes that the
incoming and outgoing areas are always referenced off the same base
register. If they aren't, then the routine returns no overlap.
But we'd need to consider the case where we have a reference to the arg
or frame pointer which later gets rewritten into a stack pointer
relative address.
Is it too late at the point were you do the checks to reject the sibling
call? If not, then maybe the overlap routine should return a tri-state.
No overlap, overlap, don't know. The last would be used when the two
addresses use a different register.
Jeff
