[LLVMbugs] [Bug 3311] New: llvm-gcc bootstrap broken on x86-64 linux

[bugzilla-daemon at cs.uiuc.edu]

http://llvm.org/bugs/show_bug.cgi?id=3311

           Summary: llvm-gcc bootstrap broken on x86-64 linux
           Product: new-bugs
           Version: unspecified
          Platform: Other
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: new bugs
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: baldrick at free.fr
                CC: llvmbugs at cs.uiuc.edu


Fails during stage2, when running the compiler built with the compiler
built during stage1:

xgcc ... -g0 -finhibit-size-directive -fno-inline-functions -fno-exceptions
-fno-zero-initialized-in-bss -fno-toplevel-reorder  -fno-omit-frame-pointer
-fno-asynchronous-unwind-tables \
          -c ../../gcc-4.2.llvm/gcc/crtstuff.c -DCRT_BEGIN \
          -o crtbegin.o
In file included from /usr/include/string.h:423,
                 from ../../gcc-4.2.llvm/gcc/tsystem.h:103,
                 from ../../gcc-4.2.llvm/gcc/crtstuff.c:68:
/usr/include/bits/string2.h: In function ‘__strpbrk_c2’:
/usr/include/bits/string2.h:1129: internal compiler error: Segmentation fault


Steps to reproduce: bootstrap llvm-gcc.  A non-bootstrap build is not enough.
I see this on two different x86-64 linux boxes.

Bisection shows it was broken by this commit:

------------------------------------------------------------------------
r61847 | evancheng | 2009-01-07 03:08:57 +0100 (Wed, 07 Jan 2009) | 10 lines

The coalescer does not coalesce a virtual register to a physical register if
any of the physical register's sub-register live intervals overlaps with the
virtual register. This is overly conservative. It prevents a extract_subreg
from being coalesced away:

v1024 = EDI  // not killed
      =
      = EDI

One possible solution is for the coalescer to examine the sub-register live
intervals in the same manner as the physical register. Another possibility is
to examine defs and uses (when needed) of sub-registers. Both solutions are too
expensive. For now, look for "shortvirtual intervals" and scan instructions to
look for conflict instead.

This is a small win on x86-64. e.g. It shaves 403.gcc by ~80 instructions.

------------------------------------------------------------------------


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