[Bug target/53659] New: ARM: Using -mcpu=cortex-a9 option results in bad performance for Cortex-A9 processor in C-Ray phoronix benchmark

[siarhei.siamashka at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53659

             Bug #: 53659
           Summary: ARM: Using -mcpu=cortex-a9 option results in bad
                    performance for Cortex-A9 processor in C-Ray phoronix
                    benchmark
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: target
        AssignedTo: unassig...@gcc.gnu.org
        ReportedBy: siarhei.siamas...@gmail.com


gcc version 4.7.0
--with-arch=armv7-a --with-float=hard --with-fpu=neon --with-mode=thumb

$ cd /tmp
$ wget http://www.phoronix-test-suite.com/benchmark-files/c-ray-1.1.tar.gz
$ tar -xzf c-ray-1.1.tar.gz
$ cd c-ray-1.1

$ make clean && make
gcc -O3 -ffast-math   -c -o c-ray-mt.o c-ray-mt.c
gcc -o c-ray-mt c-ray-mt.o -lm -lpthread
$ ./c-ray-mt -t 32 -s 160x120 -r 8 -i sphfract -o output.ppm
c-ray-mt v1.1
Rendering took: 6 seconds (6683 milliseconds)

$ sed -i "s,-O3,-O3 -mcpu=cortex-a9,g" Makefile

$ make clean && make
gcc -O3 -mcpu=cortex-a9 -ffast-math   -c -o c-ray-mt.o c-ray-mt.c
gcc -o c-ray-mt c-ray-mt.o -lm -lpthread
$ ./c-ray-mt -t 32 -s 160x120 -r 8 -i sphfract -o output.ppm
c-ray-mt v1.1
Rendering took: 7 seconds (7906 milliseconds)

Comparing to the default -march=armv7-a configuration, -mcpu=cortex-a9 caused a
~18% slowdown (7906 milliseconds vs. 6683 milliseconds). The test was run on a
dual-core ARM Cortex-A9 @1.2GHz