llvm-ld missing a dce pass

[llvmbot]

Bugzilla Link	1311
Resolution	FIXED
Resolved on	Feb 22, 2010 12:52
Version	trunk
OS	Linux
Reporter	LLVM Bugzilla Contributor

Extended Description

I ran "llvm-ld -O4" on some bytecode I had to hand, and noticed the
following in the result:

    %tmp3.i = load i8* getelementptr 

(%struct.system__restrictions__rident__restrictions_info*
@​system__restrictions__run_time_restrictions, i32 0, i32 2, i32 1) ;
[#uses=1]
icmp eq i8 %tmp3.i, 0 ; :0 [#uses=0]

The second line is the only use of the first line, and the
second line has no uses! "opt -dce" cleans this up, so presumably
llvm-ld could do with an extra dce pass.

[lattner]

This should do it:
http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20070402/046846.html

There is no testcase, so no way to verify it.

Someone should eventually go through the llvm-ld passes and clean them up.

-Chris

[llvmbot]

The passes were directly extracted from gccld. What needs to be cleaned up?

[lattner]

I'm not claiming gccld didn't need to be cleaned up. Note that at the end of llvm-ld, it runs instcombine
simplifycfg globaldce, (custom stuff), then runs instcombine, simplifycfg, dce, globaldce.

-Chris

[llvmbot]

Okay, you're going to need to be a little more specific with me. Describing what
passes llvm-ld runs doesn't "kick in" with me what it should be doing.

[llvmbot]

Sorry about the lack of a testcase, but the bytecode is huge and I couldn't
work out how to reduce it with bugpoint.

[llvmbot]

That did the trick - thanks Chris!