similar to: [LLVMdev] stack usage and scoping

Hello, Scott > I've just started using LLVM for a project I'm working on, and the > docs seem to encourage the use of alloca, with the expectation that > various optimization passes will optimize away unnecessary stack > pressure.  However, I can't seem to figure out how LLVM can properly > re-use stack space, since it doesn't know the extend of a stack >

Ahh, this states the problem precisely. Does anyone know if there is active development in this direction? I'd love to be able to use llvm.lifetime.start() / end(). Scott On Fri, Dec 11, 2009 at 12:12 PM, Anton Korobeynikov <anton at korobeynikov.info> wrote: > Hello, Scott > >> I've just started using LLVM for a project I'm working on, and the >> docs seem

Hi again. I have a complex type system in my custom language that isn't easily representable as LLVM IR types, so I figured I could mostly get along with treating my types as i8* and doing the appropriate bitcasts and inttoptr instructions, and doing pointer arithmetic myself (by casting the pointers to ints, adding the appropriate byte offsets, and then casting back to pointers). However,

On Thu, May 10, 2018 at 10:35 PM, whitequark <whitequark at whitequark.org> wrote: > On 2018-05-11 02:28, Andrew Kelley via llvm-dev wrote: > >> In the Zig frontend, we know at compile-time the entire call graph. >> This means we know stack size for all functions and therefore the >> upper bound stack usage. >> >> [snip] >> 1. Is there a way to

Hi everyone, I'm curious about the constraints that come with the usage of llvm.stacksave/llvm.stackrestore. Specifically I was wondering what the contract of their usage was with respect to SSA variables defined after llvm.stacksave. It seems to me that they could get spilled to a stack slot, which I'm concerned stackrestore might mess up. Is this a valid concern? Thanks, Keno

On 2018-05-11 02:28, Andrew Kelley via llvm-dev wrote: > In the Zig frontend, we know at compile-time the entire call graph. > This means we know stack size for all functions and therefore the > upper bound stack usage. > > [snip] > 1. Is there a way to accomplish this with existing LLVM API? You should use the @llvm.stacksave and @llvm.stackrestore intrinsic. It is only legal

Hi, I've tracked the first problem (mentioned in my previous email, quoted below) down further, ending up in the handling of alloca in LoopRotation.cpp (from trunk): // If the instruction's operands are invariant and it doesn't read or write // memory, then it is safe to hoist. Doing this doesn't change the order of // execution in the preheader, but does

Hi, I have two problems regarding the llvm.stackrestore intrinsic. I'm running on 3.0, but a quick test on trunk also showed the same behavior. First problem: --------------- I have code like: tmp1 = call llvm.stacksave() tmp2 = alloca [do some stuff with tmp2] call llvm.stackrestore(tmp1) [some other stuff] tmp3 = call llvm.stacksave() tmp4 = alloca [do some stuff

I wanted to mention that I'm planning to start writing and sending out patches for this. Naming the attribute 'alloca' was really confusing, so I'd like to change it to 'inalloca', which follows the preposition pattern of inreg and byval. After discussion, we decided it was silly to add stackbase uses to alloca instructions. They should stay simple. Instead, we'll

Hi Reid, On 25/07/13 23:38, Reid Kleckner wrote: > Hi LLVM folks, > > To properly implement pass-by-value in the Microsoft C++ ABI, we need to be able > to take the address of an outgoing call argument slot. This is > http://llvm.org/PR5064 . > > Problem > ------- > > On Windows, C structs are pushed right onto the stack in line with the other > arguments. In

How do you handle this during codegen? One problem is avoid stack changes (like spills). Another is coordinating things that are using allocas and those that are not but end up in the stack. Consider void foo(int arg1, int arg2, int arg3, ....CXXTypeWithCopyConstructor argn, int argp1...) You will need an alloca for argn, but the ABI also requires it to be next to the plain integers that

Hi LLVM folks, To properly implement pass-by-value in the Microsoft C++ ABI, we need to be able to take the address of an outgoing call argument slot. This is http://llvm.org/PR5064 . Problem ------- On Windows, C structs are pushed right onto the stack in line with the other arguments. In LLVM, we use byval to model this, and it works for C structs. However, C++ records are also passed this

2012/2/3 Patrik Hägglund <patrik.h.hagglund at ericsson.com>: > Hi, > > I've tracked the first problem (mentioned in my previous email, quoted > below) down further, ending up in the handling of alloca in > LoopRotation.cpp (from trunk): > >      // If the instruction's operands are invariant and it doesn't read > or write >      // memory, then it is

Hello, So, I have this testcase: void f(int n, int x[]) { if (n < 0) return; int a[n]; for (int i = 0; i < n; i++) a[i] = x[n - i - 1]; for (int i = 0; i < n; i++) x[i] = a[i] + 1; } that, compiled with -O1/-Os for AArch64 and X86, generates machine code, which fails to properly restore the stack pointer upon function return.

Hi, guys! I write a virtual machine which uses LLVM as back-end code generator. The following function code causes strange "UNREACHABLE executed!" error: define void @p1(%1*) { %2 = call i8* @llvm.stacksave() %3 = alloca %0 %4 = getelementptr %0* %3, i64 1 %5 = ptrtoint %0* %3 to i64 %6 = ptrtoint %0* %4 to i64 %7 = sub i64 %6, %5 %8 = bitcast %0* %3 to i8* call void

Hello Momchil, (CC’ing more people that could correct me if I’m wrong) Thanks for looking into this. More answers below: > On 9 Apr 2018, at 17:57, Momchil Velikov via llvm-dev <llvm-dev at lists.llvm.org> wrote: > > Hello, > > So, I have this testcase: > > void f(int n, int x[]) { > if (n < 0) > return; > > int a[n]; >

On Tue, Jul 30, 2013 at 11:07 AM, Rafael Espíndola < rafael.espindola at gmail.com> wrote: > How do you handle this during codegen? One problem is avoid stack > changes (like spills) I'm not sure I understand your question, but my plan is to basically use a frame pointer when there is a call with an argument using the 'alloca' attribute. It'll be slow but

Bringing this back up for discussion on handling exceptions. According to the inalloca design <https://llvm.org/docs/InAlloca.html>, there should be a stackrestore after an invoke in both the non-exceptional and exceptional case (that doesn't seem to be happening in some cases as we've seen, but that's beside the point). Does it make sense to model a preallocated call as

Nyx wrote: > Hello, > > I would just like to ask if it's possible to explicitly free allocas. This > is because I need to call functions that take structs of different sizes as > input, (possibly inside of loops) and I would rather avoid a stack overflow. You can't explicitly free a specific alloca, but you can use the llvm.stacksave and llvm.stackrestore intrinsics to

Jay, do you have a PowerPC64 target? If so, could you please check attached patch on PPC box? This is a draft patch, but it would be nice to make sure that we are moving to right direction here. Thanks, -Maxim On 18/11/15 00:12, Jay Foad wrote: >>> Currently test/asan/TestCases/alloca_vla_interact.cc is XFAILed for >>> powerpc64. I've had a look at why it