[Bug tree-optimization/80884] New: [8 regression] test case gcc.target/powerpc/20050830-1.c fails starting with r247886

["seurer at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80884

            Bug ID: 80884
           Summary: [8 regression] test case
                    gcc.target/powerpc/20050830-1.c fails starting with
                    r247886
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: seurer at gcc dot gnu.org
  Target Milestone: ---

This test fails on power6 (BE obviously) but still works on power7 and later. 
The test case is looking for a specific assembler instruction

spawn -ignore SIGHUP /home/seurer/gcc/build/gcc-trunk-p6/gcc/xgcc
-B/home/seurer/gcc/build/gcc-trunk-p6/gcc/
/home/seurer/gcc/gcc-trunk-p6/gcc/testsuite/gcc.target/powerpc/20050830-1.c
-fno-diagnostics-show-caret -fdiagnostics-color=never -O2 -ffat-lto-objects -S
-o 20050830-1.s
PASS: gcc.target/powerpc/20050830-1.c (test for excess errors)
FAIL: gcc.target/powerpc/20050830-1.c scan-assembler bdn

and the assembler output changed like this from r247885 to r247886:

seurer@makalu-lp1:~/gcc/build/gcc-test$ diff 20050830-1.s.old 20050830-1.s.new
19,30c19,29
<       addis 10,2,.LC0@toc@ha
<       addi 9,3,-512
<       rldicl 9,9,56,40
<       addi 9,9,1
<       ld 8,.LC0@toc@l(10)
<       addi 10,3,-256
<       sldi 3,3,2
<       cmpwi 7,10,256
<       mtctr 9
<       add 3,3,8
<       li 9,42
<       blt 7,.L7
---
> 	addis 9,2,.LC0@toc@ha
> 	addi 10,3,-512
> 	rlwinm 10,10,0,0,23
> 	subf 10,10,3
> 	ld 8,.LC0@toc@l(9)
> 	sldi 10,10,2
> 	sldi 9,3,2
> 	addi 7,8,-1024
> 	add 9,9,8
> 	add 10,10,7
> 	li 8,42
33,35c32,35
<       stw 9,0(3)
<       addi 3,3,-1024
<       bdnz .L3
---
> 	stw 8,0(9)
> 	addi 9,9,-1024
> 	cmpld 7,9,10
> 	bne 7,.L3
38,41d37
< .L7:
<       li 10,1
<       mtctr 10
<       b .L3
45c41
<       .ident  "GCC: (GNU) 8.0.0 20170511 (experimental) [trunk revision
247885]"
---
> 	.ident	"GCC: (GNU) 8.0.0 20170511 (experimental) [trunk revision 247886]"


When I tried it with a compiler built for power7 there was no difference is the
assembly before/after this revision.