bugpoint should fork/exec opt instead of fork/exec'ing itself to run opt passes

[lattner]

Bugzilla Link	753
Resolution	FIXED
Resolved on	Aug 05, 2010 10:26
Version	1.0
OS	All

Extended Description

Currently, BugDriver::runPasses exec's bugpoint with a magic argument to run passes, instead of running
opt.

It would be nice if bugpoint was changed to run opt. Because the eventual instructions it prints will use
opt, it knows how to do it already. In most cases there should be no difference. In cases where the
optimizer is nondeterministic or thrashing memory though, it is possible that bugpoint can find a
problem, reduce it, then it may not be reproducible with the opt command line that is printed.

By always using what it will eventually print, bugpoint is more likely to do a useful reduction.

-Chris

[lattner]

assigned to @nlewycky

[nlewycky]

proposed patch
Nothing fancy; I just hard-coded "opt" instead of looking up ToolName (which is used for 'bugpoint' in error messages).

I haven't really tested this since I don't have anything handy, but I'll leave it in my tree until I'm confident with it, or I get a positive review.

[nlewycky]

I've been testing with this for a while now, and I've only found one bug. It seems that it will find my installed version of 'opt' instead of the just compiled version.

It should try looking for the tool based on the path of bugpoint itself, first.

[llvmbot]

patch
Tested by running

./Debug+Asserts/bin/bugpoint -debug -inline -run-llc ~/test.ll

and checking that the debug line has commands like:

Running selected passes on program to test for crash:
About to run: ./Debug+Asserts/bin/opt -o bugpoint-output.bc -inline bugpoint-input.bc-tLS4sj

*** Attempting to perform final cleanups:
About to run: ./Debug+Asserts/bin/opt -o bugpoint-output.bc -globaldce -deadarghaX0r -deadtypeelim bugpoint-input.bc-I7UmY2

[llvmbot]

Fixed in 110333.