On 08/06/2013 03:57 AM, Kirill Yukhin wrote:
> On 05 Aug 09:55, Richard Henderson wrote:
>> On 08/05/2013 08:07 AM, Kirill Yukhin wrote:
>>> Hello Richard, Vlad,
>>>
>>> On 31 Jul 06:26, Richard Henderson wrote:
>>>> On 07/31/2013 05:02 AM, Kirill Yukhin wrote:
>>>>>
>>>>> There's ICE (max. number of generated reload insns per insn is achieved
>>>>> (90)),
>>>>> when LRA tried to save mask register before call. This was caused by fact
>>>>> that split_reg function
>>>>> in lra-constraints.c allocates memory for saved reg in
>>>>> SECONDARY_MEMORY_NEEDED_MODE which
>>>>
>>>> I've told you before that it's not SECONDARY_MEMORY that you want, but
>>>> a secondary reload. You should be patching ix86_secondary_reload, right
>>>> below where we handle QImode spills from non-Q registers for x86-32.
>>>
>>> Trying to do that with no success so far.
>>> Could you pls correct me if I am wrong.
>>> What I am trying to do is to introduce 2 new `define_expand' for load and
>>> store.
>>
>> Huh? You shouldn't need this.
>>
>> Give me a test case and I can have a look at it.
>
> Hello,
>
> I've squashed part 1 and 2 + rebased on recent trunk.
> Testcase is attached.
> To reproduce: build-x86_64-linux/gcc/xgcc -Bbuild-x86_64-linux/gcc -Ofast
> -mavx512f -march=core-avx2 repro.c -S -o- -ffixed-rsi -ffixed-rdi
> -ffixed-rbx -ffixed-rbp -m32
>
> Thanks a lot for help!
You've found what I believe to be a bug in LRA.
Specifically, lra-constraints.c split_reg uses SECONDARY_MEMORY_NEEDED_MODE to
choose what mode to spill a caller-save register. Given the existing
definition in i386.h, this tries to spill a MASK_CLASS register in SImode. But
MASK_CLASS does not support SImode, only QI/HImode. Which leads to substantial
confusion in the allocator trying to satisfy the move.
I believe the use of SECONDARY_MEMORY_NEEDED_MODE in split_reg is wrong.
What's the history behind that, Vlad? Surely we can spill the value in
its current mode?
Certainly this patch fixes the crash from Kirill's reproducer...
r~
* lra-constraints.c (split_reg): Always spill in the current mode.
diff --git a/gcc/lra-constraints.c b/gcc/lra-constraints.c
index 728c058..924d588 100644
--- a/gcc/lra-constraints.c
+++ b/gcc/lra-constraints.c
@@ -4388,11 +4388,7 @@ split_reg (bool before_p, int original_regno, rtx insn,
rtx next_usage_insns)
{
enum machine_mode sec_mode;
-#ifdef SECONDARY_MEMORY_NEEDED_MODE
- sec_mode = SECONDARY_MEMORY_NEEDED_MODE (GET_MODE (original_reg));
-#else
sec_mode = GET_MODE (original_reg);
-#endif
new_reg = lra_create_new_reg (sec_mode, NULL_RTX,
NO_REGS, "save");
}
