Testing LLVM 3.0 on Ubuntu 11.10 ARM

LLVM 3.0 was released some time ago and I’ve thought it’ll be good to give it a try on stock Ubuntu 11.10 ARM. That means I’ve tested LLVM 3.0 with Ubuntu provided GNU C++ 4.6.1 and Clang 2.9. GNU C++ configuration looks:

$ gcc -v
Using built-in specs.
Target: arm-linux-gnueabi
Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro 4.6.1-9ubuntu3' --with-bugurl=file:///usr/share/doc/gcc-4.6/README.Bugs --enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-4.6 --enable-shared --enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.6 --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-plugin --enable-objc-gc --enable-multilib --disable-sjlj-exceptions --with-arch=armv7-a --with-float=softfp --with-fpu=vfpv3-d16 --with-mode=thumb --disable-werror --enable-checking=release --build=arm-linux-gnueabi --host=arm-linux-gnueabi --target=arm-linux-gnueabi
Thread model: posix
gcc version 4.6.1 (Ubuntu/Linaro 4.6.1-9ubuntu3) 

I’ve compiled LLVM 3.0 by those two compilers with default configuration and then with optimization flags set to -O0, -O1, -O2 and -O3. The table below lists sum of unexpected failures and unexpected passes with appropriate links to the tests output files. What’s surprising to me is that Clang on ARM even in version 2.9 performs so well. I know, Clang depends on LLVM and LLVM by default checks for Clang as a preferred compiler and both projects are mainly developed by Apple’s engineers, but still this is on native ARM/Linux system, so nothing like cross-compilation from MacOSX/x64 to iOS/ARM!

-O0 -O1 -O2 -O3 default
GCC 4.6.1 6 6 51 51 51
Clang 2.9 1147 8 12 12 12

So as you can see GCC still wins on the lowest number of failures while using -O0/-O1, but Clang performs very well on -O2/-O3/default optimization levels. Please note that the excess number of failures on -O0 with Clang is probably caused by the fact that LLVM code requires some optimization to be performed on it to behaves correctly and it looks like Clang does not perform such optimization while GCC does when compiling with -O0.
Also what’s kind of surprise to me is to see Clang compilation performance. I’ve not marked hard numbers since this was not the task for this testing, but I’ve been surprised to see what GCC took around 700 minutes, Clang did in about 400 minutes. I’m talking about default compilation on i.MX53 Quick Start Board here.

Now the questions are: how Clang compiled LLVM affects GHC tests and GHC compilation speed? (i.e. I may use -O3 compiled LLVM for this). Also how would the numbers look like while testing latest greatest Linaro GCC and Clang 3.0? Perhaps material for another post or two…


LLVM patch is merged for inclusion in LLVM 3.0 release

Good news for those shy to patch LLVM source code and build from scratch. 🙂 The patch which adds GHC calling convention for ARM platform is merged for inclusion in LLVM 3.0 release. This is mainly due to David Terei persistence and constant push on Apple engineering to get it in since I’ve submitted the patch for inclusion just last day and was not able to answer all the questions arising from it. David not only replied with all needed information, but also kept emailing LLVM 3.0 release engineer and asking for inclusion. Thanks David!