[Bug tree-optimization/69036] New: g++ hangs compiling tree-ssa-loop-ivopts.c at -O3

[gary at intrepid dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69036

            Bug ID: 69036
           Summary: g++ hangs compiling tree-ssa-loop-ivopts.c at -O3
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gary at intrepid dot com
  Target Milestone: ---

While trying to build and bootstrap GCC at -O3 (using
--with-build-config=bootstrap-O3) on an x86-64, the compiler hangs in the final
stage while trying to build tree-ssa-loop-ivopts.o.  As shown below, the
failure can be triggered by doing a regular bootstrap build and then forcing
the compilation of tree-ssa-loop-ivopts.c at -O3.  Interestingly, it does not
replicate _unless_ the compiler is fully bootstrap, which may indicate there is
an issue with GCC (prev-gcc) compiling itself.  Also, when the compiler hangs,
it appears that its memory requirement steadily climbs over time.

The first failing version appears to be this one:

r231674 | rguenth | 2015-12-16 01:21:04 -0800 (Wed, 16 Dec 2015) | 8 lines

2015-12-16  Richard Biener  <rguenther@suse.de>

        PR tree-optimization/68892
        * tree-vect-slp.c (vect_analyze_slp_cost_1): Properly compute
        cost for permuted loads.

        * gcc.dg/vect/bb-slp-pr68892.c: New testcase.

Steps to reproduce.

1. Standard configure and make.

(cd ./src; svn up -q -r231674)
src=`cd src; pwd`
rm -rf bld
mkdir bld
cd bld
$src/configure
nj=`getconf _NPROCESSORS_ONLN`
make -j$nj >& make.log

2. cd into gcc build directory and attempt to remake tree-ssa-loop-ivopts.o at
-O3.

cd gcc
rm tree-ssa-loop-ivopts.o
make CXXFLAGS='-O3 -g' tree-ssa-loop-ivopts.o
[compiler hangs]