On Nov 12, 2007, at 12:19 PM, Andrew Coppin wrote:
Hi guys.
I just removed GHC 6.6.1 and installed 6.8.1, and I noticed something rather unexpected. I recompiled an existing program (with -O2), and instead of taking 30 seconds to compile, it took roughly 2 seconds. That's a really serious speedup! o_O Anybody have any idea what might have caused this? (Not, you understand, that I'm complaining! But the release notes say 10-15% faster, not 15,000% faster...)
One of the main reasons for this is that GHC no longer defaults to compiling via C when -O2 is enabled. In 6.6.1, it would generate C code and then run the C compiler on that, by default. Now, by default, it just generates assembly code directly. Both C and assembly generation are available in both versions (using the -fvia-C and -fasm flags, respectively) but 6.8.1 improved the assembly backend enough that it made sense to make it the default. Aaron