[Bug target/69252] New: [4.9/5/6 Regression] gcc.dg/vect/vect-iv-9.c FAILs with -Os -fmodulo-sched -fmodulo-sched-allow-regmoves -fsched-pressure

[zsojka at seznam dot cz]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69252

            Bug ID: 69252
           Summary: [4.9/5/6 Regression] gcc.dg/vect/vect-iv-9.c FAILs
                    with -Os -fmodulo-sched -fmodulo-sched-allow-regmoves
                    -fsched-pressure
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: zsojka at seznam dot cz
  Target Milestone: ---
              Host: x86_64-pc-linux-gnu
            Target: powerpc64-unknown-linux-gnu

Created attachment 37319
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=37319&action=edit
reduced testcase

Output (qemu userspace emulation used):
$ powerpc64-unknown-linux-gnu-gcc -v
Using built-in specs.
COLLECT_GCC=/repo/gcc-trunk/binary-trunk-232261-checking-yes-rtl-df-nographite-powerpc64/bin/powerpc64-unknown-linux-gnu-gcc
COLLECT_LTO_WRAPPER=/repo/gcc-trunk/binary-trunk-232261-checking-yes-rtl-df-nographite-powerpc64/bin/../libexec/gcc/powerpc64-unknown-linux-gnu/6.0.0/lto-wrapper
Target: powerpc64-unknown-linux-gnu
Configured with: /repo/gcc-trunk//configure --enable-languages=c,c++
--enable-checking=yes,rtl,df --without-cloog --without-ppl --without-isl
--build=x86_64-pc-linux-gnu --host=x86_64-pc-linux-gnu
--target=powerpc64-unknown-linux-gnu
--with-ld=/usr/bin/powerpc64-unknown-linux-gnu-ld
--with-as=/usr/bin/powerpc64-unknown-linux-gnu-as
--with-sysroot=/usr/powerpc64-unknown-linux-gnu --disable-multilib
--disable-libstdcxx-pch
--prefix=/repo/gcc-trunk//binary-trunk-232261-checking-yes-rtl-df-nographite-powerpc64
Thread model: posix
gcc version 6.0.0 20160112 (experimental) (GCC) 

$ powerpc64-unknown-linux-gnu-gcc -Os -fmodulo-sched
-fmodulo-sched-allow-regmoves -fsched-pressure testcase.c

$ ./a.out 
qemu: uncaught target signal 6 (Aborted) - core dumped
Aborted

Only powerpc64 seems to be affected.

The wrong code seems to be:
.L.main1:
        li 9,0
        addis 5,2,.LC1@toc@ha           # gpr load fusion, type long
        ld 5,.LC1@toc@l(5)
        li 10,24
        mtctr 10
        sldi 6,9,2
        lwzx 10,5,6
        addi 9,9,1
        sldi 6,9,2
        add 7,10,8
        mr 8,9
...

r8 is used uninitialised here (it has value 25 set by the caller).
r8 always stores the value of r9 from the previous iteration, but here, it is
unset.

Something like:
@@ -21,6 +21,7 @@
        li 10,24
        mtctr 10
        sldi 6,9,2
+       mr 8,9
        lwzx 10,5,6
        addi 9,9,1
        sldi 6,9,2

would fix the example.

The code emitted without -fmodulo-sched-allow-regmoves is much smaller (the
partial unrolling is not done).

Tested revisions:
trunk r232261 - FAIL
5-branch r232254 - FAIL
4_9-branch r232213 - FAIL
4_8-branch r224828 - FAIL
4_7-branch r211571 - OK
4_6-branch r197894 - OK
4_5-branch r189152 - OK