similar to: Understand alias-analysis results

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 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

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 LLVM developers, We tried to find if there are some passes in LLVM do the opposite of the SROA(Scalar Replacement of Aggregates) pass, but did not find one. Do we have this kind of pass to bring back the structure type? Or this is done separately in any transformation passes? Thanks, Lin-Ya -------------- next part -------------- An HTML attachment was scrubbed... URL:

> > Okay, it's just not immediately undefined behaviour. The C model has more > issues because of the problem with how "trap representation" is defined > (which precludes trap representations for unsigned char, two's complement > signed char, etc.). This interpretation is further stressed because C only explicitly ascribes > undefined behaviour to trap

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 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() { >>>>

Hello all, Thank everyone who participated in the (impromptu) round table discussion on Tuesday. For those who are interested, I share the summary of the discussion. Also, I share a short-term plan regarding this issue and relevant patches. *Fixing Miscompilations using Freeze* ----------------------------------- To reduce the cost of fixing miscompilations using freeze instruction, we need to

I have three modules: ----------------------------------------------------------------- s1.ll: %0 = type <{ i32, i32 }> define void @s1(%0* byval %myStruct) nounwind { return: ret void } ----------------------------------------------------------------- s2.ll: %0 = type <{ i32, i32 }> define void @s2(%0* byval %myStruct) nounwind { return: ret void }

Hi, Scalar evolution seems to be wrapping around the trip count in the following loop. void add (int *restrict a, int *restrict b, int *restrict c) { char i; for (i = 0; i < 255; i++) a[i] = b[i] + c[i]; } When I run scalar evolution on the bit code, I get a backedge-taken count which is obviously wrong. $> cat loop.ll ; Function Attrs: nounwind define void @add(i32* noalias

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

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:

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 Xiaoyi, this looks like a bug to me - please file a bug report. Ciao, Duncan. On 01/11/12 04:35, Guo, Xiaoyi wrote: > I have three modules: > ----------------------------------------------------------------- > s1.ll: > > %0 = type <{ i32, i32 }> > > define void @s1(%0* byval %myStruct) nounwind { > return: > ret void > } >

It is UB when a poison is passed to certain operations that raise UB on poison, such as division by poison/dereferencing poison pointer/branching on poison condition/etc. Otherwise, poison is simply propagated, but it does not raise UB Copying poison bytes is okay: // Members are initialized to poison at object creation. p = alloca {i8, i32} // p[0], p[4~7] are poison q = alloca {i8, i32} // we

Hi, I have the following IR code </snippet> %prev = getelementptr inbounds %struct.myStruct* %node, i32 0, i32 1 %1 = load %struct.myStruct** %prev, align 4, !tbaa !0 %next1 = getelementptr inbounds %struct.myStruct* %1, i32 0, i32 0 store %struct.myStruct* %0, %struct.myStruct** %next1, align 4, !tbaa !0 %2 = load %struct.myStruct** %prev, align 4, !tbaa ! </snippet> myStruct is

Hi Devs, debug info emitted by llvm does not contain DW_AT_Location for Formal parameter if it is an aggregate like below case 1) aggregate contain more than 4 homogeneous and size more than 128 bits i.e. typedef struct{ int a,b,c,d,e; }mystruct; void foo(mystruct ms){ } 2) aggregate contain hetrogeneous type and size more than 128 bits. i.e. typedef struct{ int a,b; float c,d,e; }mystruct; void

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

> > // Members are initialized to poison at object creation. >> p = alloca {i8, i32} // p[0], p[4~7] are poison >> p[0] is an i8, so it shouldn't be poison? > > My interpretation of standard is that reading uninitialized char can also yield trap representation. If uninitialized, char variable has indeterminate value, and C/C++ does not seem to forbid reading trap