Patches and some potential bugs

These should add xIDs for several passes. Please let me know if there're
any problems with the code. I'm a very novice C++ and LLVM programmer,
so please bear with me.

The patches look great, applied:


I ran into something suspicious:
carrot:~/tmp> llvm-dis test5.c -o test5.ll
llvm-dis: Invalid bytecode signature: 636E6923 (Vers=0, Pos=4)

llvm-dis does not disassemble .c files, it disassembles .bc files. "llvm-gcc" is what turns .c files into LLVM code.

carrot:~/tmp> which llvm-dis
carrot:~/tmp> which llvm-gcc
carrot:~/tmp> llvm-dis --version
Low Level Virtual Machine (llvm) 1.7 (see DEBUG BUILD
carrot:~/tmp> llvm-gcc --version
llvm-gcc (GCC) 4.0.1 LLVM (Apple Computer, Inc. build 5400)
Copyright (C) 2005 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is

It seems that debug build of llvm-dis incorrectly complains about the
bytecode signature (regular build disassembles it fine).

I don't think the regular build does. Did you forget a 'b'?

Second, -W[al],-disable-opt don't work with the new frontend for some

carrot:~/tmp/hsat> llvm-gcc -lm -Wl,-disable-opt hsat.c -o
/usr/bin/ld: bad -rpath option
collect2: ld returned 1 exit status

carrot:~/tmp/hsat> llvm-gcc -lm -Wa,-disable-opt hsat.c -o
as: unrecognized option `-disable-opt'

Right. The old front-end uses a hack to run the LLVM optimizers, where it replaces the 'as' and 'ld' tools with the LLVM "gccas" and "gccld" tools. Because of this, there was no clean way to pass -O options down to these tools and we end up with really horrible and ugly options like -Wa,-disable-opt.

The new front-end is a step in a much better direction. :slight_smile: The equivalent to:

$ llvm-gcc3 -Wa,-disable-opt hsat.c -o hsat.bc -c

is now:

$ llvm-gcc4 -O0 hsat.c -o hsat.bc -c -emit-llvm

To turn on (some) optimizations, you can pass -O[123] to llvmgcc4. Beware that I haven't gotten around to installing the full optimization pipeline in llvm-gcc4 though, so to get the equivalent of:

$ llvm-gcc3 hsat.c -o hsat.bc -c

I suggest using:

$ llvm-gcc4 -O3 hsat.c -o - -S -emit-llvm | gccas > hsat.bc

This will run exactly the same set of optimizations as the llvm-gcc3 does (literally, by using the same tool :).

Note that llvmgcc4 does not currently have any wrapper to run the link-time optimizer (gccld) yet. As such, you'll have to run it manually if you are interested.

At some point in the future, when I (or someone else) gets around to plumbing up the optimization options better, it is likely that -emit-llvm will continue to work as it does now (it outputs LLVM code at any optimization level), but that the common way of using llvm-gcc4 in IPO mode will be to pass -O4. Thus, if you compile and link your program with "llvm-gcc -O4 ..." you will get transparent IPO support.

I have many other projects to tackle, before this is a priority, but I'll file a bugzilla bug to track this if someone is interested in helping out.


This is now PR763 for any who are interested: