[LLVMbugs] [Bug 12400] New: libLTO.dylib crashes with "We only handle reachable blocks"

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=12400

             Bug #: 12400
           Summary: libLTO.dylib crashes with "We only handle reachable
                    blocks"
           Product: clang
           Version: unspecified
          Platform: PC
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: LLVM Codegen
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: nicolasweber at gmx.de
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified


The repro for this is "build chromium with LTO", so I'm not sure how useful
having this bug is. If you don't think it's actionable, feel free to close.

1.) enable lto for chromium
a) Add LLVM_LTO to the gyp file, and disable -dead_strip as that makes ld crash
a lot earlier (wendling is working on this):
http://codereview.chromium.org/9789003/diff/6001/build/common.gypi
b) Disable debug symbols, else ld will need over 22 GB of ram
(GYP_DEFINES='fastbuild=1 dcheck_always_on=1' build/gyp_chromium)
c) (If you use ninja or make, teach tools/gyp/pylib/gyp/xcode_emulation.py
about LLVM_LTO, it's just translated to -flto in cflags.)

2.) Build chrome. Linking Chromium Framework will take about 2.5h, then it'll
die with:

Assertion failed: (isReachableFromEntry(DefBB) && isReachableFromEntry(UseBB)
&& "We only handle reachable blocks"), function dominates, file
/Volumes/MacintoshHD2/src/chrome-git/src/third_party/llvm/lib/VMCore/Dominators.cpp,
line 92.
Stack dump:
0.    Running pass 'Function Pass Manager' on module 'ld-temp.o'.
1.    Running pass 'Global Value Numbering' on function
'@_ZN7cricket11StunMessage4ReadEPN9talk_base10ByteBufferE'
clang: error: unable to execute command: Illegal instruction
clang: error: linker command failed due to signal (use -v to see invocation)
ninja: build stopped: subcommand failed.

real    149m49.710s
user    316m36.118s
sys    19m33.936s

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