[llvm-dev] LLVM Backend for a platform with no (normal) stack

[Anton Korobeynikov via llvm-dev]

Well, since you're having memory, then things are more or less doable
– all you need is to create and maintain stack by yourself. This could
be done on per-function basis or whole program (the technique is
called "compiled stack" or "software stack").
On Fri, Dec 14, 2018 at 11:09 PM JD Jones via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
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> Thanks, no malloc or free equivalents either (no heap).
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> So, there are no others (to your knowledge) who have built an LLVM backend for a platform with no “normal” stack?  I found a presentation about some FPGA work (using LLVM) but it doesn’t seem to apply to my platform. Perhaps someone else on the mailing list will have come across this rarity?
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> Thank you again for your time and responses. If I have inadvertently been rude, please forgive someone new to LLVM? And if your forgiveness stretches that far, perhaps you could clue me on just how I was rude so that I can avoid it in the future?
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> More thanks,
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> JD Jones
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> From: Bruce Hoult [mailto:brucehoult at sifive.com]
> Sent: Friday, December 14, 2018 1:29 PM
> To: jjones at prc-hsv.com
> Cc: LLVM Developers Mailing List <llvm-dev at lists.llvm.org>
> Subject: Re: [llvm-dev] LLVM Backend for a platform with no (normal) stack
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> Having your function prologue call malloc() and epilogue call free() (or similar functions) instead of bumping a stack pointer is not a problem. That stuff is generated explicitly by ISA-specific code anyway.
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> On Fri, Dec 14, 2018 at 9:05 AM JD Jones <jjones at prc-hsv.com> wrote:
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> Thanks for your response.  Please see below.
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> From: Bruce Hoult [mailto:brucehoult at sifive.com]
> Sent: Thursday, December 13, 2018 5:58 PM
> To: jjones at prc-hsv.com
> Cc: LLVM Developers Mailing List <llvm-dev at lists.llvm.org>
> Subject: Re: [llvm-dev] LLVM Backend for a platform with no (normal) stack
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> Do you have a register that you can store a memory address
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> >> yes
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> in and an addressing mode that allows you to add (or subtract) a constant to that register
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> >> Sometimes
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> and use the address calculated to load//store from memory? Do you have enough registers that you can keep one of them permanently pointed to a particular memory region?
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> >> No
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> The platform intentionally does not allow use of some large chunk of memory for shared use by function calls.  I can allocate memory (so long as I know the necessary size before-hand). I can work around this issue, but if someone has already addressed it, I’d like to learn from their experiences before rolling my own.
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> If yes, then you have a stack to exactly the same extent as RISC-V or MIPS do.
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> On Thu, Dec 13, 2018 at 12:53 PM JD Jones via llvm-dev <llvm-dev at lists.llvm.org> wrote:
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> Dear Sir or Ma’am;
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> I have found a wealth of help and information on writing an LLVM backend. And, my platform has no stack.
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> Can you point me to any information that would specifically address creating a backend for this kind of platform?
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> In previous wanderings, I thought I ran across a phrase “platforms with no stack such as FPGAs”, but I can’t find that mention, now.
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> More thanks than I can type,
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> JD Jones
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> Software Engineer
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>
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-- 
With best regards, Anton Korobeynikov
Department of Statistical Modelling, Saint Petersburg State University