[patch] hotspot miscompilation of OpenJDK6 with gcc from the gcc-4_3-branch

[Matthias Klose]

OpenJDK (using the IcedTea6 build and patches) fails to build with 4.3 from the
4.3 branch, when the jvm built in stage1 is used for the first time in the
stage2 build:

-def-pcompile:
    [javac] Compiling 2 source files to
/scratch/packages/openjdk/x/openjdk-6-6b11/openjdk/control/build/linux-i586/langtools/build/toolclasses
WARNING: Default charset US-ASCII not supported, using ISO-8859-1 instead
    [javac]
/scratch/packages/openjdk/x/openjdk-6-6b11/openjdk/langtools/make/tools/CompileProperties/CompileProperties.java:26:
cannot access unnamed package
    [javac] ANSI_X3.4-1968
    [javac] import java.io.BufferedWriter;
    [javac] ^

BUILD FAILED

the build failure is not seen when reverting r136501; seen as well when just
reverting the two hunks for record_numbers_of_iterations.

seen with -O3 and -O2, not -O1.

not seen on amd64 and sparc (the other two archs using OpenJDK hotspot).

the miscompiled file is ciTypeFlow.cpp, compiled using
g++-4.3 -fpic -fno-rtti -fno-exceptions -D_REENTRANT -fcheck-new -g -m32
-march=i586 -mtune=generic -O2 -fno-strict-aliasing -DVM_LITTLE_ENDIAN
-Wpointer-arith -Wconversion -Wsign-compare -c ciTypeFlow.cpp


Upstream GCC [1] doesn't agree on a bug in the compiler, but in the application
code:

  "I belive this is just INVALID.  The code seems to do lots of things with
  this enum Cell, but the C++ compiler is allowed to just allocate 1 bit of
  storage for it.

  Maybe changing the Cell declaration to

    enum Cell { Cell_0, Cell_max = UINT_MAX }

  fixes the issue.

  See 7.2/6 for the standard wording."

The suggested fix is attached; I don't see any regressions. IcedTea currently
has a patch to work around the problem, compiling this file with -fno-ivopts.

   Matthias

[1] http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36917
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