[zebes:~] astrange% /usr/local/bin/g++fsf -v
Using built-in specs.
Target: powerpc-apple-darwin7.7.0
Configured with: ../fsfgcc/configure --program-suffix=fsf
--enable-languages=c,c++,java,treelang --
enable-cpu=750
Thread model: posix
gcc version 4.1.0 20050321 (experimental)
[zebes:~] astrange% /usr/local/bin/g++fsf -fdump-tree-gimple
-fdump-tree-optimized -Os
-mmultiple -S -mcpu=750 -mtune=750 -dp ccset.cpp
The source is
unsigned int ccblah(unsigned int *q,unsigned int B,unsigned int D,unsigned int
E,unsigned int
F,unsigned int H)
{
bool cfold1, cfold2, cfold3, cfold4, cfold5, cfold6;
cfold1 = D == B;
cfold2 = B == F;
cfold3 = D == H;
cfold4 = F == H;
cfold5 = !cfold1 && !cfold4;
cfold6 = !cfold3 && !cfold2;
q[0] = cfold1 && cfold6 ? D : E;
q[1] = cfold2 && cfold5 ? F : E;
q[2] = cfold3 && cfold5 ? D : E;
q[3] = cfold4 && cfold6 ? F : E;
return ((cfold1) ^ (cfold2))?E:F;
}
Except for the return, it's a simplified testcase of
http://scale2x.sourceforge.net/'s core.
GCC generates this for the first block:
__Z7ccblahPjjjjjj:
LFB3:
xor r12,r5,r4 ; 30 *rs6000.md:11675/1 [length = 12]
subfic r0,r12,0
adde. r12,r0,r12
xor r10,r7,r8 ; 27 *rs6000.md:11645/1 [length = 12]
subfic r0,r10,0
adde r10,r0,r10
xor r4,r4,r7 ; 19 *rs6000.md:11645/1 [length = 12]
subfic r0,r4,0
adde r4,r0,r4
xor r11,r5,r8 ; 23 *rs6000.md:11645/1 [length = 12]
subfic r0,r11,0
adde r11,r0,r11
beq- cr0,L27 ; 31 *rs6000.md:13791 [length = 4]
li r2,0 ; 34 *movsi_internal1/5 [length = 4]
b L29 ; 151 jump [length = 4]
The xor/subfic/adde patterns are unnecessary; instead, it should be using cmpw
into four different CR
subregisters ("cmpw cr1,r5,r4" "cmpw cr2,r7,r8" etc).
For the return statement, GCC generates:
L47:
cmpw cr7,r30,r4 ; 127 *cmpsi_internal1 [length = 4]
stw r0,12(r11) ; 125 *movsi_internal1/4 [length = 4]
bne+ cr7,L48 ; 128 *rs6000.md:13791 [length = 4]
mr r3,r7 ; 131 *movsi_internal1/1 [length = 4]
L48:
lmw r30,-8(r1) ; 169 *lmw [length = 4]
blr ; 170 *return_internal_si [length = 4]
There may be a possible savings by using crxor instead of another cmpw.
--
Summary: PowerPC - inefficient use of condition register
Product: gcc
Version: 4.1.0
Status: UNCONFIRMED
Severity: enhancement
Priority: P2
Component: rtl-optimization
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: astrange at ithinksw dot com
CC: gcc-bugs at gcc dot gnu dot org
GCC target triplet: powerpc-apple-darwin7.7.0
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20614
