[llvm-dev] Opt can't find 'hello' pass

[Arthur Eubanks via llvm-dev]

Adding the -debug-pass-manager flag to the opt commands shows what's
going on:

Starting llvm::Module pass manager run.
Running pass: VerifierPass on C:/src/tmp/a.ll
Running analysis: VerifierAnalysis on C:/src/tmp/a.ll
Running analysis: InnerAnalysisManagerProxy<llvm::FunctionAnalysisManager,
llvm::Module> on C:/src/tmp/a.ll
Starting llvm::Function pass manager run.
Skipping pass HelloWorldPass on foo due to optnone attribute
Skipping pass: HelloWorldPass on foo
Finished llvm::Function pass manager run.
Running pass: VerifierPass on C:/src/tmp/a.ll
Finished llvm::Module pass manager run.

The optnone attribute on a function makes most function passes skip running
on the function. You got the IR from the output of clang -O0 which adds
that attribute. This is actually briefly mentioned at the end of
https://llvm.org/docs/WritingAnLLVMNewPMPass.html.
Perhaps we can make HelloWorldPass required for demonstration purposes and
to avoid this specific problem in the future.

On Wed, Feb 10, 2021 at 4:48 PM Joshua R Hilke <jrhilke at mit.edu> wrote:

> cat hello.ll
>
> ; ModuleID = 'hello.c'
> source_filename = "hello.c"
> target datalayout =
> "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
> target triple = "x86_64-unknown-linux-gnu"
>
> ; Function Attrs: noinline nounwind optnone uwtable
> define dso_local i32 @foo() #0 {
> entry:
>   %a = alloca i32, align 4
>   store i32 1, i32* %a, align 4
>   %0 = load i32, i32* %a, align 4
>   ret i32 %0
> }
>
> attributes #0 = { noinline nounwind optnone uwtable
> "disable-tail-calls"="false" "frame-pointer"="all"
> "less-precise-fpmad"="false" "min-legal-vector-width"="0"
> "no-infs-fp-math"="false" "no-jump-tables"="false"
> "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false"
> "no-trapping-math"="true" "stack-protector-buffer-size"="8"
> "target-cpu"="x86-64" "target-features"="+cx8,+fxsr,+mmx,+sse,+sse2,+x87"
> "tune-cpu"="generic" "unsafe-fp-math"="false" "use-soft-float"="false" }
>
> !llvm.module.flags = !{!0}
> !llvm.ident = !{!1}
>
> !0 = !{i32 1, !"wchar_size", i32 4}
> !1 = !{!"clang version 13.0.0 (https://github.com/llvm/llvm-project.git
> 16e7973c5d8fb543ea9e91735be8610a8b1c262a)”}
>
>
> $BUILD_DIR/bin/opt -disable-output hello.ll -passes=helloworld
>
> *nothing gets printed*
>
> On Feb 10, 2021, at 3:23 PM, Arthur Eubanks <aeubanks at google.com> wrote:
>
> Can you post the .ll file that doesn't work and the command you ran?
>
> On Wed, Feb 10, 2021 at 3:21 PM Joshua R Hilke <jrhilke at mit.edu> wrote:
>
>> Got it. Thank you. I tried using the new pass manager from the new
>> tutorial as well but was having an issue where the ‘helloworld’ pass would
>> only work if I manually removed all the metadata from my hello.ll file to
>> where the only thing in it was the function. Otherwise, it would run
>> silently and not print out any function names. Any solution to that?
>>
>>
>> On Feb 10, 2021, at 2:11 PM, Arthur Eubanks <aeubanks at google.com> wrote:
>>
>> That's due to the recent transition to the new pass manager. Adding
>> -enable-new-pm=0 to the opt command should work.
>>
>> I'll update the documentation to explicitly say that the legacy pass
>> manager is no longer the default in big red letters.
>>
>> On Wed, Feb 10, 2021 at 1:49 PM Joshua R Hilke via llvm-dev <
>> llvm-dev at lists.llvm.org> wrote:
>>
>>> I’m just trying to run the hello world example from the LLVM Writing a
>>> Pass Tutorial (https://llvm.org/docs/WritingAnLLVMPass.html), but
>>> whenever I run:
>>>
>>> $BUILD_DIR/bin/clang -c -emit-llvm hello.c
>>>
>>> $BUILD_DIR/bin/opt -load $BUILD_DIR/lib/LLVMHello.so -hello < hello.bc >
>>> /dev/null
>>>
>>>
>>>
>>> I get the following error:
>>>
>>> bin/opt: unknown pass name ‘hello’
>>>
>>>
>>>
>>> Which seems odd because if I run:
>>>
>>> $BUILD_DIR/bin/opt -load $BUILD_DIR/lib/LLVMHello.so --help | grep hello
>>>
>>>
>>> I get:
>>>
>>> --hello  - Hello World Pass
>>>
>>>
>>> To build LLVM I’m running the following commands from my build directory:
>>>
>>> cmake -G Ninja -DLLVM_ENABLE_PROJECTS=‘clang’ ../llvm
>>>
>>> cmake --build .
>>>
>>>
>>> Just to clarify, I’m not writing my own pass. Just trying to run the
>>> ‘hello’ pass that comes default when building LLVM
>>>
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> llvm-dev at lists.llvm.org
>>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>
>>
>>
>
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