Hey,
Are you on mozilla-central or on an older release branch? I'm asking
because we switched the default register allocator from linear scan to the
backtracking allocator on mozilla-central. On older branches, the
backtracking allocator is only used for asm.js code. You could try with
--ion-regalloc=backtracking and --ion-regalloc=lsra and see if it makes a
difference.
So r3 is your stack pointer, right? One thing that comes to mind is
OffsetToOtherHalfOfNunbox, you probably have to change the TYPE_INDEX and
PAYLOAD_INDEX constants that are used there.
Jan
On Sun, Mar 22, 2015 at 8:52 PM, Cameron Kaiser <ckai...@floodgap.com>
wrote:
> Ion doesn't seem to respect how a Nunbox is laid out on big-endian
> platforms (I imagine this is not very surprising). Consider this simple
> script:
>
> js --ion-eager -e 'var i,j=0; for(i=0;i<50000;i++) { j+=i } print(j)'
>
> On big-endian, this asserts immediately with
>
> Assertion failure: safepoint->hasNunboxPayload(alloc)
>
> The stack value slot is at offset 8, but the stack payload slot is at 4.
>
> If I go into LIR.h and change the code from
>
> bool hasNunboxPayload(LAllocation payload) const {
> if (payload.isArgument())
> return true;
> if (payload.isStackSlot() && hasValueSlot(payload.
> toStackSlot()->slot())
> )
> return true;
>
> to
>
> bool hasNunboxPayload(LAllocation payload) const {
> if (payload.isArgument())
> return true;
> if (payload.isStackSlot() &&
> hasValueSlot(payload.toStackSlot()->slot()
> + NUNBOX32_PAYLOAD_OFFSET)
> )
> return true;
>
> the assertion is satisfied, but the code generated is wrong. Oddly, stores
> are correct, but loads are not. Here is one extract (PowerPC):
>
> 0x00fedd00: lwz r5,2704(r3) ; load actually comes from type
> 0x00fedd04: trap ; debugging, ignore
> 0x00fedd08: addo r6,r5,r4 ; add with overflow
> 0x00fedd0c: mfxer r12
> 0x00fedd10: mtcrf 128,r12
> 0x00fedd14: clrlwi r12,r12,3
> 0x00fedd18: mtxer r12
> 0x00fedd1c: nop
> 0x00fedd20: nop
> 0x00fedd24: nop
> 0x00fedd28: nop
> 0x00fedd2c: bgt- 0xfee9d8
> 0x00fedd30: stw r6,2708(r3) ; store actually stores to payload
>
> Note the two offsets are off by NUNBOX32_PAYLOAD_OFFSET, which on
> big-endian systems is 4.
>
> I can't figure out where to change how stack slots are allocated so that
> the value slot and the payload slot match and generate the right code. Any
> suggestions?
>
> Cameron Kaiser
>
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