similar to: [LLVMdev] Meaning of byval?

errata: I am on 3.6 full stop. I *thought* there was a 3.7 available, based on the title of http://llvm.org/docs/ ("LLVM 3.7 documentation"). I suppose the docs are ahead of the release schedule? On Sun, Mar 8, 2015 at 9:44 AM Mircea Trofin <mtrofin at google.com> wrote: > Sorry, that phase is part of the PNaCl toolchain. This would be LLVM 3.6, > would your comments still

Hi Duncan, On 11/10/12 15:47, Duncan Sands wrote: > Hi Roel, > >> When going through the internals of the old C back-end, I see that the CBE >> encapsulates arrays into a struct. The source code has the following comment to >> explain this behaviour. >> >> // Arrays are wrapped in structs to allow them to have normal >> // value semantics

Hi Tim, Thank you for the input. I think I follow you. I believe the LowerCall is doing what it needs to do - passing pointer either on the stack or in register as per ABI. The LowerFormalArguments() is where I am stuck. LowerFormalArguments () calls CCInfo.AnalyzeFormalArguments(Ins, CC_XCore), which calls the CC_XCore(). This is where I placed the CCIfByVal<CCPassByVal<0,4>> which

Hi, > I believe the LowerCall is doing what it needs to do - passing pointer either on the stack or in register as per ABI. >From very quick test-cases with no understanding of XCore, that looks plausible. > LowerFormalArguments () calls CCInfo.AnalyzeFormalArguments(Ins, CC_XCore), which calls the CC_XCore(). > This is where I placed the CCIfByVal<CCPassByVal<0,4>>

LLVM developers, I was wondering if the program would still be safe if I strip the byval attributes from the parameters in the entire bitcode. LLVM language reference manual states that "The attribute implies that a hidden copy of the pointee is made between the caller and the callee, so the callee is unable to modify the value in the callee. This attribute is only valid on LLVM pointer

Duncan wrote: > Hi Alon, > > > The docs say "[byval] indicates that the pointer parameter should > > really be passed by value to the function. The attribute implies > > that a hidden copy of the pointee is made between the caller and > > the callee, so the callee is unable to modify the value in the > > callee." > > > > I am not sure what

Hello guys, For single scalar pointer parameter, we have 'byval' to specify the pointee is not changed. But for base+range parameters like: declare void @_gfortran_transfer_integer_write(%struct.__st_parameter_dt*, i8*, i32) (This is the fortran runtime api to 'printf' one integer) The 2nd & 3rd args are used to specify the memory of that integer. I didn't find a

Hi, after working with llvm for a while, I'm still a little confused with the meaning of the 'byval' attribute. From the langref: "This indicates that the pointer parameter should really be passed by value to the function. The attribute implies that a hidden copy of the pointee is made between the caller and the callee, so the callee is unable to modify the value in the callee.

Hi Tim, I may be missing something but using CCPassByVal is moving the pointer onto the stack - not what I'm after. I need to add an operation to the function prolog that actually makes a copy of the pointed to data. It is the responsibility of the callee to make the copy, not the caller - hence my trouble. (currently the callee can corrupt the original data viz pass-by-reference!) This

Hi - help! I have read through previous threads on the subject of 'byval' e.g. https://groups.google.com/forum/#!topicsearchin/llvm-dev/Exact$20meaning$20of$20byval/llvm-dev/cyRZyXcMCNI https://groups.google.com/forum/#!topicsearchin/llvm-dev/$20byval/llvm-dev/uk4uiK93jeM https://groups.google.com/forum/#!topicsearchin/llvm-dev/byval/llvm-dev/46Tv0lSRwBg and read through code

Hi Tim, Correction to my last email. What I should have said is that the new pointer is used by the callee rather than the original byVal pointer arg. (the byVal pointer arg remains but is not used by the callee). viz: define void @f1(%struct.tag* byval) { entry: %st = alloca %struct.tag, align 4 %1 = bitcast %struct.tag* %st to i8* %2 = bitcast %struct.tag* %0 to i8* call void

Hi, In the past months, several options have been presented for making byval (and similar attributes, such as inalloca or sret) work with opaque pointers. The main two I've seen were byval(T) and byval(N) where N is the size of T. They both have their upsides and downsides, for example: byval(T) would be a type-parametric attribute, which, AFAIK, does not already exist and may complicate

Hi Robert, > I tried adding to the XCoreCallingConv.td: > CCIfByVal<CCPassByVal<0,4>> // pushes pointer to the stack This looks sensible to me. After that it comes down to cooperation between XCoreISelLowering's LowerFormalArguments and LowerCall functions. LowerFormalArguments is at the beginning of a function and is responsible for taking arguments out of

Matthijs Kooijman wrote: > Hi, > > after working with llvm for a while, I'm still a little confused with the > meaning of the 'byval' attribute. From the langref: > > "This indicates that the pointer parameter should really be passed by value to > the function. The attribute implies that a hidden copy of the pointee is made > between the caller and the

Hello, I am seeking a clarification of the semantics of 'byval' parameter attribute in llvm IR. Let's assume the ABI says the caller should create the 'hidden copy' of the pointee. My question is which part of the compiler chain should generate the alloca and copy code. My understanding is that it is the target code generator, not the provider of the llvm IR. But given the

Hi Tim, Thought about it last night and was coming to the same conclusion. 1. it cant be done at the end during lowering (target backend). 2. it should be part of llvm as the byVal needs to be handled. As a twist, I have been told that llvm-gcc can lower byVal into memcpy in the callee. I may take a look at this. I wonder if it ever emits 'byVal'... I still feel I don't understand

Unfortunately this is what I'm already doing, and it's not working. I drew inspiration from a disassembly of a program that showed that struct foo { int a; float b; char buf[80]; } struct foo get_foo(void) { foo f = { 5, 2.5 }; return f; } would turn into define void @get_foo(%struct.foo* sret %agg.result) nounwind ssp { ... call void @llvm.memcpy.p0i8.p0i8.i64(i8* %2, i8*

> Do all tests need it? Align is just for non-default alignment (> align(1)) so it may be OK for the tests to omit it & it's probably not right to /require/ an align attribute on a byval parameter. I've had to fix some of the tests which checked that the right alignment was applied, by looking at the generated asm, but had no "align A" attributes and relied on the

I have a question about a problem I came across while I was adding support for aggregate va_arg expression in clang. The following is the example program I will use in this email. I compile the program with clang targeting mips. Note that I have not pushed all the changes I have made yet, so you will not be able to see the same results. $ clang -ccc-host-triple mipsel-unknown-linux

Hi, Thanks for the help. I tried this out, but on x86_64 and with llvm 2.6 and llvm-gcc 4.2.1, I dont seem to get an aligned variable. This is the function definition that I have define internal fastcc void @walksub(%struct.hgstruct* noalias nocapture sret %agg.result, %struct.node* %p, double %dsq, %struct.hgstruct* byval align 64 %hg, i32 %level) nounwind { And these are the call sites,