similar to: @llvm.memcpy not honoring volatile?

The primary reason I don’t want to provide any guarantees for what instructions are used to implement volatile memcpy is that it would forbid lowering a volatile memcpy to a library call. clang uses a volatile memcpy for struct assignment in C. For example, “void f(volatile struct S*p) { p[0] = p[1]; }”. It’s not really that useful, but it’s been done that way since before clang was written.

On Wed, 5 Jun 2019 at 13:49, Eli Friedman via llvm-dev <llvm-dev at lists.llvm.org> wrote: > I don’t see any particular reason to guarantee that a volatile memcpy will access each byte exactly once. How is that useful? I agree it's probably not that useful, but I think the non-duplicating property of volatile is ingrained strongly enough that viewing a memcpy as a single load and

I agree, this is a bug. John On 6/7/19 11:48 AM, JF Bastien via llvm-dev wrote: > > >> On Jun 5, 2019, at 2:28 PM, Tim Northover via llvm-dev <llvm-dev at lists.llvm.org> wrote: >> >> On Wed, 5 Jun 2019 at 13:49, Eli Friedman via llvm-dev >> <llvm-dev at lists.llvm.org> wrote: >>> I don’t see any particular reason to guarantee that a volatile

> On Jun 11, 2019, at 6:27 AM, Guillaume Chatelet <gchatelet at google.com> wrote: > > I spent some time reading the C standard <https://web.archive.org/web/20181230041359if_/http://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf>: > > 5.1.2.3 Program execution > 2. Accessing a volatile object, modifying an object, modifying a file, or calling

On 11/11/2015 8:53 AM, Hal Finkel wrote: > > SROA seems to be doing a number of things here. What about if we prevented SROA from generating multiple slices splitting volatile accesses? There might be a significant difference between that and something like this test (test/Transforms/SROA/basictest.ll): > > define i32 @test6() { > ; CHECK-LABEL: @test6( > ; CHECK: alloca i32 >

> could you allocate the memory on the stack instead (alloca instruction)? This is mainly for string or binary blob handling, using the stack isn't a great idea for size reasons. While I'm experimenting with simple code examples now, and I picked a simple one for this email. I'm certain things will get much more complicated once I implement more features of the language. On Tue,

The new @llvm.memcpy API does not have an alignment parameter. Instead the docs say to use the align <n> attribute. How is this supposed to work with different alignments? For example, I have one memcpy with align 4, align 4, and another with align 1, align 1. ; Function Attrs: argmemonly nounwind declare void @llvm.memcpy.p0i8.p0i8.i64(i8* nocapture writeonly align 4, i8* nocapture

The front end I'm building for an existing interpreted language is unfortunately producing output similar to this far too often; define void @foo(i8* nocapture %dest, i8* nocapture %src, i32 %len) nounwind { %1 = tail call noalias i8* @malloc(i32 %len) nounwind tail call void @llvm.memcpy.p0i8.p0i8.i32(i8* %1, i8* %src, i32 %len, i32 1, i1 false) tail call void

On Jan 18, 2018, at 10:48 PM, Chris Lattner <clattner at nondot.org<mailto:clattner at nondot.org>> wrote: On Jan 18, 2018, at 7:45 AM, Daniel Neilson via llvm-dev <llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote: Hi all, This change has been reviewed, and appears to be ready to land (review available here if anyone still wants to chime in:

On 3/22/2018 3:15 PM, Andrew Kelley via llvm-dev wrote: > The new @llvm.memcpy API does not have an alignment parameter. Instead > the docs say to use the align <n> attribute. How is this supposed to > work with different alignments? > > For example, I have one memcpy with align 4, align 4, and another with > align 1, align 1. > > ; Function Attrs: argmemonly

Hi, I'm trying to get AA results for two pointers, but it seems that AA cannot look though a memcpy. For example: define dso_local spir_func void @fun() { entry: ; Store an address of `var' %var = alloca i32, align 4 store i32 42, i32* %var, align 4 %var.addr = alloca i32*, align 8 store i32* %var, i32** %var.addr, align 8 ; Memcpy

> On Jan 18, 2018, at 7:45 AM, Daniel Neilson via llvm-dev <llvm-dev at lists.llvm.org> wrote: > > > Hi all, > This change has been reviewed, and appears to be ready to land (review available here if anyone still wants to chime in: https://reviews.llvm.org/D41675 <https://reviews.llvm.org/D41675> ). The process that we’re going to use for landing this will take a few

SROA optimization pass did some optimizations and transforms for memcpy function,such as ld/st operations.When someone has written down code like size>sizeof(dest) in memcpy(*dest,*src,size), there was much likely a wrong code generation.for example,considered as such testcase: int main() { char ch; short sh = 0x1234; memcpy(&ch,&sh,2); printf("ch=0x%02x\n",ch); } At

Hi, I am hoping that someone can help me figure out how to prevent the insertion of "memcpy" from the assembly source. My target is an instruction set simulator that doesn't support this. Thank you for your valuable time. Wolf *Here are my compile commands:* $ clang -emit-llvm -fno-builtin -o3 --target=mips -S matrix_float.c -o vl_matrix_float.ll $ llc vl_matrix_float.ll *IR

On 12/5/18 9:51 AM, Andrew Savonichev via llvm-dev wrote: >> Hi, >> >> I'm trying to get AA results for two pointers, but it seems that AA >> cannot look though a memcpy. For example: >> >> define dso_local spir_func void @fun() { >> entry: >> ; Store an address of `var' >> %var = alloca i32, align 4 >>

Hi all, This change has been reviewed, and appears to be ready to land (review available here if anyone still wants to chime in: https://reviews.llvm.org/D41675 ). The process that we’re going to use for landing this will take a few steps. To wit: Step 1) Remove align argument, and add align attribute to pointer args. Require that src & dest have the same alignment via verifier rule. Also

On 12/5/18 2:14 PM, Andrew Savonichev wrote: >> On 12/5/18 9:51 AM, Andrew Savonichev via llvm-dev wrote: >>>> Hi, >>>> >>>> I'm trying to get AA results for two pointers, but it seems that AA >>>> cannot look though a memcpy. For example: >>>> >>>> define dso_local spir_func void @fun() { >>>>

Hi all, A quick note just to let people know that as of this past Friday my go at this work has been fully landed. It ended up being a back-burner item, so it took longer than I would have liked to get completed. None the less, the changes made were: 1) The IRBuilders in LLVM, Clang, and Polly were all updated to create only the new form of the memory intrinsics. 2) All LLVM passes to understand

Hi Daniel, a quick question (and kind-of a follow-up to <https://lists.llvm.org/pipermail/llvm-dev/2017-July/115665.html>): Do the pointers have to be aligned even if the size is 0? It would be nice to have this stated explicitly in the LangRef. Kind regards, Ralf On 26.03.2018 22:43, Daniel Neilson via llvm-dev wrote: > Hi all, >  A quick note just to let people know that as of

Hi Thanks ! so for this example void foo(X &src, X &dst) { dst = src; } and the IR: define void @foo(X&, X&)(%struct.X* dereferenceable(8), %struct.X* dereferenceable(8)) #0 { %3 = alloca %struct.X*, align 8 %4 = alloca %struct.X*, align 8 store %struct.X* %0, %struct.X** %3, align 8 store %struct.X* %1, %struct.X** %4, align 8 %5 = load %struct.X*,