similar to: Difference between clang -O1 -Xclang -disable-O0-optnone and clang -O0 -Xclang -disable-O0-optnone in LLVM 9

You can also add the -Xclang -disable-O0-optnone flag to your command line. This will disable the implicit optnone when compiling with O0. Cheers, Michael On Mon, Sep 18, 2017 at 7:27 AM +0200, "Craig Topper via llvm-dev" <llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote: To prevent optnone from being added you can replace -O0 with "-O1 -Xclang

Hi, We have a research LLVM-based domain-specific code generator that we want to upgrade form LLVM 4.0 to 5.0. The code generator is written as an out-of-tree loadable module for opt. Till Clang 4.0 we were compiling the front-end code (annotated C++) using -O0. The generated bitcode was further processed using opt with our module loaded. In Clang 5.0 we see that using -O0 adds the optnone

Have -O0 on your clang command line causes all functions to get marked with an 'optnone' attribute that prevents opt from being able to optimize them later. You should also add "-Xclang -disable-O0-optnone" to your command line. ~Craig On Thu, Sep 21, 2017 at 10:04 PM, Yi Lin via llvm-dev < llvm-dev at lists.llvm.org> wrote: > Hi all, > > I am trying to

@Craig and @Michael After installing clang-5.0 (download from http://releases.llvm.org, does not have Flang build's slowdown mention above), 1. clang++ -O0 -Xclang -disable-O0-optnone -Xclang -disable-llvm-passes -c -emit-llvm -o a.bc LULESH.cc; opt -O3 a.bc -o b.bc; llc -O3 -filetype=obj b.bc -o b.o ; clang++ b.o -o b.out; ./b.out 20 runtime: 2.354069e+01 2. clang++ -O1 -Xclang

Thanks a lot, it is clear to me now. BTW, for Clang's slowdown, I submit an issue here: https://github.com/flang-compiler/flang/issues/356 I have no idea about the root cause. Maybe due to debug symbols. But, I already use -DCMAKE_BUILD_TYPE=Release. Anyway, I believe there is a bug somewhere. On Sat, Jan 6, 2018 at 3:43 PM, Craig Topper <craig.topper at gmail.com> wrote: >

-disable-O0-optnone has no effect with anything other than -O0. -O0 being passed to clang also causes all functions to be marked noinline. I don't know if there is a command line option to turn that off. I recommend passing "-O1 -Xclang -disable-llvm-passes" to clang. Passing -O0 very specifically means disable optimizations. ~Craig On Sat, Jan 6, 2018 at 12:25 PM, toddy wang

Why are you using build directions from "flang" which is a fortran compiler and maintained by different people than the LLVM/clang community? But then compiling C/C++ code? Their bug database should be used for filing bugs against the fortran compiler not a C/C++ compiler issue. ~Craig On Sat, Jan 6, 2018 at 1:04 PM, toddy wang <wenwangtoddy at gmail.com> wrote: > Thanks a

What I am trying is to compile a program with different sets of optimization flags. If there is no fine-grained control over clang optimization flags, it would be impossible to achieve what I intend. Although there is fine-grained control via opt, for a large-scale projects, clang-opt-llc pipeline may not be a drop-in solution. On Fri, Jan 5, 2018 at 10:00 PM, Craig Topper <craig.topper at

I don't think "clang -help" prints options about optimizations. Clang itself doesn't have direct support for fine grained optimization control. Just the flag for levels -O0/-O1/-O2/-O3. This is intended to be simple and sufficient interface for most users who just want to compile their code. So I don't think there's a way to pass just -dse to clang. opt on the other hand

On Jan 7, 2018 8:46 PM, "toddy wang" <wenwangtoddy at gmail.com> wrote: @Sean, here is my summary of several tools. Format: (ID,tool, input->output, timing, customization, questions) 1. llc, 1 bc -> 1 obj, back-end compile-time (code generation and machine-dependent optimizations), Difficult to customize pipeline, N/A 2. LLD: all bc files and obj files -> 1 binary

On Jan 5, 2018 11:30 PM, "toddy wang via llvm-dev" <llvm-dev at lists.llvm.org> wrote: What I am trying is to compile a program with different sets of optimization flags. If there is no fine-grained control over clang optimization flags, it would be impossible to achieve what I intend. LLD has -lto-newpm-passes (and the corresponding -lto-newpm-aa-pipeline) which allows you to

Craig, thanks a lot! I'm actually confused by clang optimization flags. If I run clang -help, it will show many optimizations (denoted as set A) and non-optimization options (denoted as set B). If I run llvm-as < /dev/null | opt -O0/1/2/3 -disable-output -debug-pass=Arguments, it also shows many optimization flags (denote as set C). There are many options in set C while not in set A,

O0 didn't start applying optnone until r304127 in May 2017 which is after the 4.0 family was branched. So only 5.0, 6.0, and trunk have that behavior. Commit message copied below Author: Mehdi Amini <joker.eph at gmail.com> Date: Mon May 29 05:38:20 2017 +0000 IRGen: Add optnone attribute on function during O0 Amongst other, this will help LTO to correctly handle/honor

@Sean, do you mean llc ? For llc 4.0 and llc 5.0, I cannot find -lto-newpm-passes option, is it a hidden one? On Sat, Jan 6, 2018 at 7:37 PM, Sean Silva <chisophugis at gmail.com> wrote: > > > On Jan 5, 2018 11:30 PM, "toddy wang via llvm-dev" < > llvm-dev at lists.llvm.org> wrote: > > What I am trying is to compile a program with different sets of >

No, I meant LLD, the LLVM linker. This option for LLD is relevant for exploring different pass pipelines for link time optimization. It is essentially equivalent to the -passes flag for 'opt'. Such a flag doesn't make much sense for 'llc' because llc mostly runs backend passes, which are much more difficult to construct custom pipelines for (backend passes are often required

Hi all, I am trying to understand the effectiveness of various llvm optimisations when a language targets llvm (or C) as its backend. The following is my approach (please correct me if I did anything wrong): I am trying to explicitly control the optimisations passes in llvm. I disable optimisation in clang, but instead emit unoptimized llvm IR, and use opt to optimise that. These are what I

Hi Toddy, You can achieve what you're looking for with a pipeline based on `clang -Ox` + `opt -Ox` + `llc -Ox` (or lld instead of llc), but this won't be guarantee'd to be well supported across releases of the compiler. Otherwise, if there are some performance-releated (or not...) command line options you think clang is missing / would benefit, I invite you to propose adding them to

After build LLVM5.0, I found that clang-5.0 is extremely slow. Even it is built with -DCMAKE_BUILD_TYPE=Release For building LULESH.cc, it gets stucked at linkage stage. I build it as instructed from here https://github.com/flang-compiler/flang Maybe I should submit a bug. On Fri, Jan 5, 2018 at 8:41 PM, toddy wang <wenwangtoddy at gmail.com> wrote: > Craig, thanks a lot! > >

Hi, "SetC" options are LLVM cl::opt options, they are intended for LLVM developer and experimentations. If a settings is intended to be used as a public API, there is usually a programmatic way of setting it in LLVM. "SetA" is what clang as a C++ compiler exposes to the end-user. Internally clang will (most of the time) use one or multiple LLVM APIs to propagate a settings.

For the types of things that you are looking for, you may just want to try a bunch of -mllvm options. You can tune inlining and unrolling threshold like that, for example. On Jan 7, 2018 10:33 PM, "toddy wang via llvm-dev" <llvm-dev at lists.llvm.org> wrote: > Hi Mehdi, > > Now we have 5 pipelines. (In addition to the first 3, which I have > described in detail above,