llvm dev - Nov 2015 - DFAPacketzer, Hexagon and bundles with 1 instruction

> No. An instruction on its own is equivalent to a bundle with that
> instruction only. Also, a BUNDLE must have at least 2 instructions.
>
> -Krzysztof
>
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I'm a little confused. If a bundle is supposed to have at least 2
instructions, what is the point of
VLIWPacketzierList::isSoloInstruction(...)? Say we have an instruction that
can't be bundled with anything, how would one form a packet from it?

-- 
R
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On 11/17/2015 4:23 PM, Rail Shafigulin wrote:
>
> I'm a little confused. If a bundle is supposed to have at least 2
> instructions, what is the point of
> VLIWPacketzierList::isSoloInstruction(...)? Say we have an instruction
> that can't be bundled with anything, how would one form a packet from
it?
In the machine IR, a bundle is a regular instruction, which happens to 
have other instructions inside of it.  A basic block can have bundles 
mixed with non-bundled instructions.  If you iterate over a basic block 
using MachineBasicBlock::iterator, you will not see the contents of 
bundles, just the BUNDLE opcode.  For stepping into bundles you would 
need MachineBasicBlock::instr_iterator.

When it comes to the encoding of instructions for the hardware, the 
target-specific object-emission code must handle that properly.  That 
happens later, on a yet another program representation, where 
instructions are of type MCInst, not MachineInstr.

-Krzysztof

-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, 
hosted by The Linux Foundation

On Tue, Nov 17, 2015 at 2:35 PM, Krzysztof Parzyszek <
kparzysz at codeaurora.org> wrote:
> On 11/17/2015 4:23 PM, Rail Shafigulin wrote:
>
>>
>> I'm a little confused. If a bundle is supposed to have at least 2
>> instructions, what is the point of
>> VLIWPacketzierList::isSoloInstruction(...)? Say we have an instruction
>> that can't be bundled with anything, how would one form a packet
from it?
>>
>
> In the machine IR, a bundle is a regular instruction, which happens to
> have other instructions inside of it.  A basic block can have bundles mixed
> with non-bundled instructions.  If you iterate over a basic block using
> MachineBasicBlock::iterator, you will not see the contents of bundles, just
> the BUNDLE opcode.  For stepping into bundles you would need
> MachineBasicBlock::instr_iterator.
>
> When it comes to the encoding of instructions for the hardware, the
> target-specific object-emission code must handle that properly.  That
> happens later, on a yet another program representation, where instructions
> are of type MCInst, not MachineInstr.
>
>
> -Krzysztof
>
> --
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted
> by The Linux Foundation
>
I see. Thanks.

-- 
R
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