[LLVMdev] [RFC] Switching make check to use 'set -o pipefail'

[Rafael Espíndola]

We currently don't use pipefail when running test under make check.
This has the undesirable property that it is really easy for tests to
bitrot. For example, something like

llc %s | FileCheck %s

will still pass if llc crashes after printing what FileCheck was
looking for. It is also easy to break the tests when refactoring. I
have fixed tests that were doing

%clang_cc1 -a-driver-options ... | not grep

clearly the test was changed from %clang to %clang_cc1 and we missed
the fact that the option also had to be updated.

Currently to check a command output and that it doesn't crash we have to do

llc %s > %t
FileCheck %s < %t

I would like to switch to using pipefail instead. That would meant that a simple

llc %s | FileCheck %s

would check both llc return value and output. I have already cleared
all the tests, so all that is missing is changing lit itself. Any
objections to doing so?

Cheers,
Rafael