[LLVMbugs] [Bug 23192] New: gcc 4.9.2 suffers bootstrap comparison failures with clang 3.5.1 and later.

[bugzilla-daemon at llvm.org]

https://llvm.org/bugs/show_bug.cgi?id=23192

            Bug ID: 23192
           Summary: gcc 4.9.2 suffers bootstrap comparison failures with
                    clang 3.5.1 and later.
           Product: clang
           Version: 3.6
          Hardware: PC
                OS: All
            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 Xcode 6.3 release (with Apple Clang 6.1 compilers based on 3.6.0svn)
produces bootstrap comparison failures in the gcc 4.9.2 build on
x86_64-apple-darwin14. The same bootstrap comparison failure is also seen on
x86_64-apple-darwin13 with Xcode 6.2 but using the llvm.org clang 3.5.1, 3.5.2
or 3.6.0 compilers instead of the Apple Clang 6.0 compilers.

Comparing stages 2 and 3
warning: gcc/cc1-checksum.o differs
warning: gcc/cc1obj-checksum.o differs
warning: gcc/cc1objplus-checksum.o differs
warning: gcc/cc1plus-checksum.o differs
Bootstrap comparison failure!
gcc/asan.o differs
gcc/attribs.o differs
gcc/bitmap.o differs
gcc/c/c-decl.o differs
gcc/cfg.o differs
gcc/coverage.o differs
gcc/cp/class.o differs
gcc/cp/semantics.o differs
gcc/cp/tree.o differs
gcc/dse.o differs
gcc/dwarf2out.o differs
gcc/except.o differs
gcc/fortran/trans-common.o differs
gcc/ggc-common.o differs
gcc/graphite-clast-to-gimple.o differs
gcc/graphite.o differs
gcc/ipa-profile.o differs
gcc/ira-color.o differs
gcc/ira-costs.o differs
gcc/java/jcf-io.o differs
gcc/loop-unroll.o differs
gcc/lto-streamer-in.o differs
gcc/lto-streamer-out.o differs
gcc/objc/objc-act.o differs
gcc/objcp/objcp-act.o differs
gcc/passes.o differs
gcc/plugin.o differs
gcc/postreload-gcse.o differs
gcc/statistics.o differs
gcc/trans-mem.o differs
gcc/tree-cfg.o differs
gcc/tree-eh.o differs
gcc/tree-ssa-ccp.o differs
gcc/tree-ssa-coalesce.o differs
gcc/tree-ssa-dom.o differs
gcc/tree-ssa-live.o differs
gcc/tree-ssa-loop-ivopts.o differs
gcc/tree-ssa-phiopt.o differs
gcc/tree-ssa-pre.o differs
gcc/tree-ssa-reassoc.o differs
gcc/tree-ssa-threadupdate.o differs
gcc/tree-ssa-uncprop.o differs
gcc/tree-vectorizer.o differs
gcc/valtrack.o differs
gcc/vtable-verify.o differs
Makefile:20180: recipe for target 'compare' failed

The observation, that the llvm.org clang 3.5.1 or later compilers along side
Xcode 6.2 produces the same bootstrap comparison failure, eliminates the
cctools changes in Xcode 6.3 as the culprit and points to miscompilation of the
stage1 compiler instead.

Reducing the optimization of the stage1 bootstrap with STAGE1_CFLAGS="-O0 -g"
and STAGE1_CXXFLAGS="-O0 -g" doesn't eliminate the bootstrap comparison
failure.

Interestingly, current gcc trunk 5.0svn doesn't exhibit the bootstrap
comparison failure (with the stock build or using --enable-checking=release).

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