llvm dev - Sep 2009 - [LLVMdev] ld with gold-plugin can do this?

Hi,all

I have installed the gold-plugin and it can run correctly,but I still
have another two questions:

1.Can gold-plugin generate a bitcode file:
>From the document and also my experience on using it,"ld
-plugin...."
will only generate an executable by link several LLVM bitcode file
together,but how to make it generate a whole-program bitcode file?(even
archieve it manually is OK)

2.llvm-gcc -c will stop the linker to run:

I have been trying to generate a whole-program bitcode file,but when I
use CFLAGS="-emit-llvm -c" to compile source files into LLVM bitcode
file,llvm-gcc will not call "ld" to link modules together,so that I
cannot link these modules together automatically.

How to overcome this trouble?

Thank you !Best regards!

Nan

zhunan wrote:
> Hi,all
> 
> I have installed the gold-plugin and it can run correctly,but I still
> have another two questions:
> 
> 1.Can gold-plugin generate a bitcode file:
No. The task of linking many .bc files into a single .bc file falls on 
llvm-ld and llvm-link.

A common followup question is "but how do I link native libraries into 
my .bc file". You don't. A .bc file is llvm ir, you can't put a
native
binary library into a .bc (barring sticking it in as a string, etc).

The build then looks like:

a) 'llvm-gcc -c -flo -O2' to generate the .bc files.
b) 'llvm-ld' to combine them into a single .bc. No, not a .so nor a .a.
c) 'llc' to turn your combined .bc into a .s
d) 'as' to turn your .s into a .o
e) 'ld' to turn your .o into a .so or final executable. This is the step
where you get to specify all the native libraries to link with.

You can use 'gcc' to merge steps d and e (it just runs as and ld for 
you). Or you can use the gold plugin to merge steps b through e, but 
with the added benefit that it will optimize slightly better. See the 
llvm LTO documentation on why.
>>From the document and also my experience on using it,"ld
-plugin...."
> will only generate an executable by link several LLVM bitcode file
> together,but how to make it generate a whole-program bitcode file?(even
> archieve it manually is OK)
> 
> 2.llvm-gcc -c will stop the linker to run:
> 
> I have been trying to generate a whole-program bitcode file,but when I
> use CFLAGS="-emit-llvm -c" to compile source files into LLVM
bitcode
> file,llvm-gcc will not call "ld" to link modules together,so that
I
> cannot link these modules together automatically.
> 
> How to overcome this trouble?
You get to modify your program's build system. Things like
'configure'
work by trying to compile and run small programs. You can't run a .bc file.

Nick

A common followup question is "but how do I link native libraries into 
my .bc file". You don't. A .bc file is llvm ir, you can't put a
native
binary library into a .bc (barring sticking it in as a string, etc).

The build then looks like:

a) 'llvm-gcc -c -flo -O2' to generate the .bc files.
b) 'llvm-ld' to combine them into a single .bc. No, not a .so nor a .a.
c) 'llc' to turn your combined .bc into a .s
d) 'as' to turn your .s into a .o
e) 'ld' to turn your .o into a .so or final executable. This is the step
where you get to specify all the native libraries to link with.

You can use 'gcc' to merge steps d and e (it just runs as and ld for 
you). Or you can use the gold plugin to merge steps b through e, but 
with the added benefit that it will optimize slightly better. See the 
llvm LTO documentation on why.

[Sanjiv] - This is what PIC16 does. llvm-ld has an option called '-b'
that you can
use to specify the output bitcode file name. Unfortunately, llvm-ld always tries
to
generate a native executable (or a shell script) as well and currently there is
no way to disable that.
Maybe an option like '-no-native' will be come handy.


- Sanjiv

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