[LLVMbugs] [Bug 23183] New: clang 3.5.2 and later miscompiles llvm-gcc

[bugzilla-daemon at llvm.org]

https://llvm.org/bugs/show_bug.cgi?id=23183

            Bug ID: 23183
           Summary: clang 3.5.2 and later miscompiles llvm-gcc
           Product: clang
           Version: 3.6
          Hardware: Macintosh
                OS: MacOS X
            Status: NEW
          Severity: normal
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: howarth.mailing.lists at gmail.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

The clang compilers from 3.5.2 and later miscompile the legacy llvm-gcc code
from Apple's open source repo. The llvm-gcc bootstrap (tested with the
llvm-gcc42 fink packaging) can be restore with...

sed -i '1s/^/#pragma clang optimize off\n/'
./llvmCore/lib/CodeGen/MachineSSAUpdater.cpp
sed -i '1s/^/#pragma clang optimize off\n/'
./llvmCore/lib/Transforms/Utils/SSAUpdater.cpp

Compiling the files with -O1 is insufficient to remove the miscompilation and
-O0 is required. Disabling vectorization via the pragma statement likewise is
insufficient to eliminate the miscompilation of the code. 
    Do we have any pragma statements that would disable specific optimizations
enabled in going from -O0 to -O1?

Note that Apple clang 6.0 (based on 3.5svn) works but Apple clang 6.1 (based on
3.6svn) is broken.

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