[Bug middle-end/53676] New: [4.7/4.8 regression] constant folding regression, shown as slowdown as measured by Adobe's C++Benchmark

["matt at use dot net" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53676

             Bug #: 53676
           Summary: [4.7/4.8 regression] constant folding regression,
                    shown as slowdown as measured by Adobe's C++Benchmark
    Classification: Unclassified
           Product: gcc
           Version: 4.7.1
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: matt@use.net


The attached ZIP contains two binaries and preprocessor output files, based on
a subset of a test in Adobe's C++Benchmark suite. All GCC versions I tested
prior to 4.7 do the folding correctly. I tried using Ofast and other tricks to
workaround this new regression to no avail.

-rw-r--r-- 1 mhargett users 143573 Jun 14 15:31 int8_folding_test.gcc47.i
mhargett@chert:~/src/C++Benchmarks-gcc47-google-fast$ ./int8_folding_test-gcc46
./int8_folding_test-gcc46 

test     description   absolute   operations   ratio with
number                 time       per second   test0

 0 "int8_t constant"   0.00 sec     inf M     -nan

Total absolute time for int8_t simple constant folding: 0.00 sec
mhargett@chert:~/src/C++Benchmarks-gcc47-google-fast$ ./int8_folding_test-gcc47
./int8_folding_test-gcc47 

test     description   absolute   operations   ratio with
number                 time       per second   test0

 0 "int8_t constant"   0.69 sec   2318.84 M     1.00

Total absolute time for int8_t simple constant folding: 0.69 sec