[LLVMdev] AArch64 build error

[Tim Northover]

Hi Paul,

> I'm getting a "random" build failure related to AArch64 when building with cmake.
> The build is running with -j32 so it seems that there is some dependency issue
> that causes the build to fail when things build in a certain order.

> 3008    make[2]: *** No rule to make target `lib/Target/AArch64/AArch64GenDAGISel.inc', needed by

Hmm. That file's generated by TableGen (via some kind of custom make
magic) and included by the "regular" sources, so it's entirely
possible there's a race hiding. I always thought all TableGen commands
were run before the main sources got compiled, but at 32 threads
perhaps that doesn't matter so much.

Has this just started since AArch64 was added, or have you only
recently started building at -j32? As far as I can see AArch64 is
unexceptional in its dependencies, except for being lexicographically
the first target. I'd be interested in your results if AArch64 was
disabled.

There's clearly some issue though. I've only got 4 cores (+ 4 faked)
here so I'm not optimistic about reproducing any races you're seeing,
though I'll keep trying periodic builds. How many cores do you have
and how frequently does this seem to occur? Your host compiler and
configure command-line could be useful for controlling the environment
too.

Tim.