Hi, We have some DSP architectures (kalimba) which have 24-bits as their "minimum addressable unit". So this means that the sizeof a char (and an int and a short for that matter) is 24-bits. I quickly read the posted link WritingAnLLVMBackend.html but did not see an obvious answer to the following question: Is it possible to write a backend that faithfully represents these architectures or is sizeof_byte==8 bits baked into to llvm? Does anyone have any views on the above? thanks Matthew Gardiner On Tue, 9 Sep 2014 18:21:01 +1200 Bruce Hoult <bruce at hoult.org> wrote:> http://llvm.org/docs/WritingAnLLVMBackend.html > > > On Tue, Sep 9, 2014 at 6:09 PM, Prakash Premkumar > <prakash.prax at gmail.com> wrote: > > > How does LLVM generate machine code for different architectures? > > For example, the machine code for x86 and amd will vary. > > > > How does LLVM convert its IR to machine code for different > > architectures.Can you please explain the approach? Is it just write > > two different programs for two different architectures and pass a > > flag to the compiler based on which machine code you want to > > generate? > > > > Thanks a lot for your explanations. > > > > Thanks > > Prakash > > > > _______________________________________________ > > LLVM Developers mailing list > > LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu > > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev > > > > > > > To report this email as spam click > https://www.mailcontrol.com/sr/MZbqvYs5QwJvpeaetUwhCQ== .Member of the CSR plc group of companies. CSR plc registered in England and Wales, registered number 4187346, registered office Churchill House, Cambridge Business Park, Cowley Road, Cambridge, CB4 0WZ, United Kingdom More information can be found at www.csr.com. Keep up to date with CSR on our technical blog, www.csr.com/blog, CSR people blog, www.csr.com/people, YouTube, www.youtube.com/user/CSRplc, Facebook, www.facebook.com/pages/CSR/191038434253534, or follow us on Twitter at www.twitter.com/CSR_plc. New for 2014, you can now access the wide range of products powered by aptX at www.aptx.com.
Hi Matthew, The byte==8 bits is more of a Clang issue rather than an LLVM issue. I believe your bigger issue will be the fact that you would need to make i24's a legal type in your backend, which as far as I know (unless something has changed recently), is a _big_ job. I briefly looked into it at one point, and decided to leave it for another day. I am also unsure how hard byte=8bits is backed into Clang. You might want to ask cfe-dev. I hope that helps. Johnny On Tue, Sep 9, 2014 at 7:41 AM, Matthew Gardiner <mg11 at csr.com> wrote:> Hi, > > We have some DSP architectures (kalimba) which have 24-bits as their > "minimum addressable unit". So this means that the sizeof a char (and > an int and a short for that matter) is 24-bits. > > I quickly read the posted link WritingAnLLVMBackend.html but did not > see an obvious answer to the following question: > > Is it possible to write a backend that faithfully represents these > architectures or is sizeof_byte==8 bits baked into to llvm? > > Does anyone have any views on the above? > > thanks > Matthew Gardiner > > > On Tue, 9 Sep 2014 18:21:01 +1200 > Bruce Hoult <bruce at hoult.org> wrote: > > > http://llvm.org/docs/WritingAnLLVMBackend.html > > > > > > On Tue, Sep 9, 2014 at 6:09 PM, Prakash Premkumar > > <prakash.prax at gmail.com> wrote: > > > > > How does LLVM generate machine code for different architectures? > > > For example, the machine code for x86 and amd will vary. > > > > > > How does LLVM convert its IR to machine code for different > > > architectures.Can you please explain the approach? Is it just write > > > two different programs for two different architectures and pass a > > > flag to the compiler based on which machine code you want to > > > generate? > > > > > > Thanks a lot for your explanations. > > > > > > Thanks > > > Prakash > > > > > > _______________________________________________ > > > LLVM Developers mailing list > > > LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu > > > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev > > > > > > > > > > > > To report this email as spam click > > https://www.mailcontrol.com/sr/MZbqvYs5QwJvpeaetUwhCQ== . > > > > Member of the CSR plc group of companies. CSR plc registered in England > and Wales, registered number 4187346, registered office Churchill House, > Cambridge Business Park, Cowley Road, Cambridge, CB4 0WZ, United Kingdom > More information can be found at www.csr.com. Keep up to date with CSR on > our technical blog, www.csr.com/blog, CSR people blog, www.csr.com/people, > YouTube, www.youtube.com/user/CSRplc, Facebook, > www.facebook.com/pages/CSR/191038434253534, or follow us on Twitter at > www.twitter.com/CSR_plc. > New for 2014, you can now access the wide range of products powered by > aptX at www.aptx.com. > _______________________________________________ > LLVM Developers mailing list > LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev >-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20140909/a2a2d2cf/attachment.html>
Hi Johnny, Thanks for this - particularly the tip about cfe-dev. I'm currently trying to coerce lldb to debug these type of architectures (our current toolchain already outputs good dwarf info). However, I'm struggling since lldb has just assumes that the size of a byte is universally 8-bits. At some stage, I *think* at some stage we'd like to derive a compiler, from the "same code-base" (i.e. llvm) and I wondered how tricky this would be. Matt On Tue, 9 Sep 2014 11:49:01 +0100 Johnny Val <johnnydval at gmail.com> wrote:> Hi Matthew, > > The byte==8 bits is more of a Clang issue rather than an LLVM issue. I > believe your bigger issue will be the fact that you would need to make > i24's a legal type in your backend, which as far as I know (unless > something has changed recently), is a _big_ job. I briefly looked > into it at one point, and decided to leave it for another day. > > I am also unsure how hard byte=8bits is backed into Clang. You might > want to ask cfe-dev. > > I hope that helps. > > Johnny > > On Tue, Sep 9, 2014 at 7:41 AM, Matthew Gardiner <mg11 at csr.com> wrote: > > > Hi, > > > > We have some DSP architectures (kalimba) which have 24-bits as their > > "minimum addressable unit". So this means that the sizeof a char > > (and an int and a short for that matter) is 24-bits. > > > > I quickly read the posted link WritingAnLLVMBackend.html but did not > > see an obvious answer to the following question: > > > > Is it possible to write a backend that faithfully represents these > > architectures or is sizeof_byte==8 bits baked into to llvm? > > > > Does anyone have any views on the above? > > > > thanks > > Matthew Gardiner > > > > > > On Tue, 9 Sep 2014 18:21:01 +1200 > > Bruce Hoult <bruce at hoult.org> wrote: > > > > > http://llvm.org/docs/WritingAnLLVMBackend.html > > > > > > > > > On Tue, Sep 9, 2014 at 6:09 PM, Prakash Premkumar > > > <prakash.prax at gmail.com> wrote: > > > > > > > How does LLVM generate machine code for different architectures? > > > > For example, the machine code for x86 and amd will vary. > > > > > > > > How does LLVM convert its IR to machine code for different > > > > architectures.Can you please explain the approach? Is it just > > > > write two different programs for two different architectures > > > > and pass a flag to the compiler based on which machine code you > > > > want to generate? > > > > > > > > Thanks a lot for your explanations. > > > > > > > > Thanks > > > > Prakash > > > > > > > > _______________________________________________ > > > > LLVM Developers mailing list > > > > LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu > > > > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev > > > > > > > > > > > > > > > > > To report this email as spam click > > > https://www.mailcontrol.com/sr/MZbqvYs5QwJvpeaetUwhCQ== . > > > > > > > > Member of the CSR plc group of companies. CSR plc registered in > > England and Wales, registered number 4187346, registered office > > Churchill House, Cambridge Business Park, Cowley Road, Cambridge, > > CB4 0WZ, United Kingdom More information can be found at > > www.csr.com. Keep up to date with CSR on our technical blog, > > www.csr.com/blog, CSR people blog, www.csr.com/people, YouTube, > > www.youtube.com/user/CSRplc, Facebook, > > www.facebook.com/pages/CSR/191038434253534, or follow us on Twitter > > at www.twitter.com/CSR_plc. New for 2014, you can now access the > > wide range of products powered by aptX at www.aptx.com. > > _______________________________________________ > > LLVM Developers mailing list > > LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu > > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev > >
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