similar to: AliasAnalysis does not look though a memcpy

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 >>

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() { >>>>

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

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

[AMD Official Use Only - Internal Distribution Only] Hi, Following issue is observed with Type Based Alias Analysis(TBAA). ####################################################### struct P { float f1; float f2; float f3[3]; float f4; }; void foo(struct P* p1, struct P* p2) { p1->f2 = 1.2; p2->f1 = 3.7; } int callFoo() { struct P p; foo(&p, &(p.f2)); }

It seems the same bug is there if we do pointer swapping with selects. Do you agree? (see example below) define void @f() { entry: %a1 = alloca float, align 4 %a2 = alloca float, align 4 br label %loop end: ret void loop: %phi = phi i32 [ 0, %entry ], [ 1, %loop ] %select_cond = icmp eq i32 %phi, 0 %ptr1 = select i1 %select_cond, float* %a1, float* %a2 %ptr2 = select i1

Hi Johannes, I followed your advice and got the same result: NoAlias and No dependence. Would you say AA is faulty for saying NoAlias or DA is faulty for saying no dependence? Or both? (revised example below) Thanks! define float @f() { entry: %g = alloca float, align 4 %h = alloca float, align 4 br label %for.body for.cond.cleanup: ; preds = %for.body

Hey Matt, That's awesome. Thank you very much for all the information and clarification! Just a few follow up questions. Could you kindly shed some lights on it? Thank you! 1. I tried to tweak the code in the following way: - Clang [-> LLVM-IR]: https://llvm.godbolt.org/z/n9rGrs - [LLVM-IR ->] opt: https://llvm.godbolt.org/z/Uc6h5Y And i note that the outputs are: Alias sets for

Hi! On 7/10/2020 07:17, Shuai Wang wrote: > Hello! > > Thank you very much! Yes, that makes a lot of sense to me. However, just > want to point out two things that are still unclear: > > 1. The output contains a alias set of only one element, for instance: > "must alias, Mod       Pointers: (i32* %y, LocationSize::precise(4))" > > This one really confused

Hi again! Replying in chronological order: > On Thu, Jul 9, 2020 at 6:51 PM Shuai Wang <wangshuai901 at gmail.com > <mailto:wangshuai901 at gmail.com>> wrote: > > Hey Matt, > > That's awesome. Thank you very much for all the information and > clarification! Just a few follow up questions. Could you kindly shed > some lights on it? Thank

Hello llvm-dev, I would appreciate your feedback on the following problem. We're trying to determine whether this is a bug in LLVM or not. In the IR snippet below, we have two pointers (p and q) which initially point to two completely non-overlapping locations. Then, on every iteration of a loop, we swap the pointers and load from the first, followed by a store to the second. 1) AA says the

The frontend code is a pretty simple for loop, that counts from i = 0; i != 10; i += 1 It gets optimized into and endless loop. export fn entry() void { var array: [10]Bar = undefined; var x = for (array) |elem, i| { if (i == 1) break elem; } else bar2(); } Here's the generated IR: ; ModuleID = 'test' source_filename = "test" target datalayout =

Alias analysis is figuring out the relationship between two pointer expressions, at some location in the program. At a given point in the program, do two expressions always refer to the same location? At a given point in the program, do two expressions never refer to the same location? AliasAnalysis::alias() doesn't explicitly take a "point" in the program because we don't

Oh. So it wasn't just the memory location size that was incorrect on those aliasing checks. I took a look at the tests and it appears that the alias call also catches some cases of restrict/noalias attributes, along with the tbaa info. My first idea of constructing an alias call with no Ptr's but valid tbaa info won't catch that at least. I will create a bug report and try and see if

[AMD Public Use] Hi Oliver, I get rid of the warnings by explicitly type-casting it to struct*, and still get similar results. ####################################################### struct P { float f1; float f2; float f3[3]; float f4; }; void foo(struct P* p1, struct P* p2) { p1->f2 = 1.2; p2->f1 = 3.7; } int callFoo() { struct P p; foo(&p,

Hi I am upgrading my clang fork from 5.0 to 6.0 and I am hit by this error: Access type node must be a valid scalar type %4 = load %"struct.Foo::p.test1::"*, %"struct.Foo::p.test1::"** %_param.addr, align 8, !tbaa !16 !16 = !{!15, !15, i64 0} !15 = !{!"p.test1::", !13, i64 0, !13, i64 8} It looks like !16 is referencing !15, which is a struct. !13 is !13 =

Hi all, I am trying to use LLVM's AliasAnalysis pass, but from a standalone tool that uses llvm libraries. The following is the code snippet I am currently using. PassBuilder PB; auto mod_manager = ModuleAnalysisManager { }; PB.registerModuleAnalyses(mod_manager); AAResults& AAR = mod_manager.getResult<AAManager>(*M); But the code fails at .getResult with the following error:

Hello, I am performing alias analysis toward the following simple code: struct MyStruct { int * f1; int * f2; }; void NOALIAS(void* p, void* q){ } int main() { struct MyStruct s[2]; int a,b; s[0].f1 = &a; s[1].f1 = &b; NOALIAS(s[a].f1, s[b].f2); return 0; } When I use the following command to generate .bc code and conduct alias analysis: clang -c -emit-llvm t.c -O2 opt -basicaa

Hi Joan, On Mon, 13 May 2019 at 18:01, Joan Lluch <joan.lluch at icloud.com> wrote: > After looking at it a bit further, I think this is a Clang thing. Clang issues “align 2” if the struct has at least one int (2 bytes), but also if the entire struct size is multiple of 2. For example a struct with 4 char members. In these cases the LLVM backend correctly creates word sized load/stores

> We at Azul have been using invariant.start for marking objects as immutable after a certain point. > Also, upstream changes to teach relevant optimizations about invariant.start and end were added > last year. > > With respect to store to load forwarding, this is handled in GVN. I think the test cases in test/Transforms/GVN/invariant.start.ll > handle what you’re looking for.