The following test case illustrates an example where dcbtst instructions are
being inserted too aggressively during FDO.
Test Case:
typedef struct {
union {
short arr[64];
short arr2[8][8];
}un;
} str, *strPtr;
str blah;
int main (int argc, char *argv[])
{
int i, x, y;
strPtr ptr;
ptr = &blah;
for( y=0; y<5; y++){
for(x=0; x<=5; x++){
for (i = 0; i < (sizeof(ptr->un.arr)/8); i++) {
*(((double *) ptr->un.arr)+i) = +0.0;
}
ptr++;
}
}
return 0;
}
Commands (using gcc 4.0)
gcc -O2 -fprofile-generate -funroll-loops -o bug bug.c
./bug
gcc -O2 -fprofile-use -o bug bug.c
Generated Code - notice that a touch is done every eight bytes.
main:
stwu 1,-64(1)
li 0,5
lis 9,[EMAIL PROTECTED]
li 11,0
li 12,0
mtctr 0
la 8,[EMAIL PROTECTED](9)
stw 21,20(1)
stw 22,24(1)
stw 23,28(1)
stw 24,32(1)
stw 25,36(1)
stw 26,40(1)
stw 27,44(1)
stw 28,48(1)
stw 29,52(1)
stw 30,56(1)
stw 31,60(1)
.p2align 4,,15
.L2:
addi 22,8,128
addi 23,8,136
addi 7,8,144
addi 6,8,152
addi 5,8,160
addi 4,8,168
stw 11,0(8)
stw 12,4(8)
stw 11,8(8)
stw 12,12(8)
dcbtst 0,23
dcbtst 0,7
dcbtst 0,6
dcbtst 0,22
addi 3,8,176
addi 31,8,184
dcbtst 0,5
dcbtst 0,4
addi 30,8,192
addi 29,8,200
addi 28,8,208
addi 27,8,216
dcbtst 0,3
dcbtst 0,31
addi 26,8,224
addi 25,8,232
dcbtst 0,30
dcbtst 0,29
addi 24,8,240
addi 21,8,248
dcbtst 0,28
dcbtst 0,27
mr 9,22
addi 23,8,264
dcbtst 0,26
dcbtst 0,25
addi 22,22,128
addi 7,8,272
dcbtst 0,24
dcbtst 0,21
addi 6,8,280
addi 5,8,288
dcbtst 0,23
addi 4,8,296
addi 3,8,304
dcbtst 0,22
dcbtst 0,7
addi 31,8,312
addi 30,8,320
dcbtst 0,6
dcbtst 0,5
addi 29,8,328
addi 28,8,336
dcbtst 0,4
dcbtst 0,3
addi 27,8,344
addi 26,8,352
dcbtst 0,31
dcbtst 0,30
addi 25,8,360
addi 24,8,368
dcbtst 0,29
dcbtst 0,28
addi 21,8,376
mr 10,22
dcbtst 0,27
dcbtst 0,26
addi 23,9,264
addi 7,9,272
dcbtst 0,25
dcbtst 0,24
addi 6,9,280
addi 5,9,288
dcbtst 0,21
addi 4,9,296
addi 21,9,376
stw 11,16(8)
stw 12,20(8)
dcbtst 0,23
addi 3,9,304
stw 11,24(8)
stw 12,28(8)
dcbtst 0,7
dcbtst 0,6
addi 31,9,312
dcbtst 0,5
dcbtst 0,4
addi 30,9,320
addi 29,9,328
dcbtst 0,3
dcbtst 0,21
addi 28,9,336
addi 27,9,344
dcbtst 0,31
addi 26,9,352
addi 25,9,360
stw 11,32(8)
stw 12,36(8)
dcbtst 0,30
addi 24,9,368
stw 11,40(8)
stw 12,44(8)
dcbtst 0,29
dcbtst 0,28
addi 22,22,128
dcbtst 0,27
dcbtst 0,26
addi 23,8,520
addi 7,8,528
dcbtst 0,25
dcbtst 0,24
addi 6,8,536
addi 5,8,544
dcbtst 0,22
stw 11,48(8)
stw 12,52(8)
addi 22,8,512
addi 4,8,552
dcbtst 0,23
stw 11,56(8)
stw 12,60(8)
addi 3,8,560
dcbtst 0,7
stw 11,64(8)
stw 12,68(8)
addi 31,8,568
dcbtst 0,22
stw 11,72(8)
stw 12,76(8)
addi 30,8,576
dcbtst 0,6
stw 11,80(8)
stw 12,84(8)
addi 29,8,584
dcbtst 0,5
stw 11,88(8)
stw 12,92(8)
addi 28,8,592
dcbtst 0,4
stw 11,96(8)
stw 12,100(8)
addi 27,8,600
dcbtst 0,3
stw 11,104(8)
stw 12,108(8)
addi 26,8,608
dcbtst 0,31
stw 11,112(8)
stw 12,116(8)
addi 25,8,616
dcbtst 0,30
stw 11,120(8)
stw 12,124(8)
addi 24,8,624
dcbtst 0,29
stw 11,128(8)
stw 12,132(8)
addi 21,8,632
dcbtst 0,28
stw 11,8(9)
stw 12,12(9)
addi 22,8,640
dcbtst 0,27
stw 11,16(9)
stw 12,20(9)
addi 23,8,648
dcbtst 0,26
stw 11,24(9)
stw 12,28(9)
addi 7,8,656
dcbtst 0,25
stw 11,32(9)
stw 12,36(9)
addi 6,8,664
dcbtst 0,24
stw 11,40(9)
stw 12,44(9)
addi 5,8,672
dcbtst 0,21
stw 11,48(9)
stw 12,52(9)
addi 4,8,680
dcbtst 0,22
stw 11,56(9)
stw 12,60(9)
addi 3,8,688
dcbtst 0,23
stw 11,64(9)
stw 12,68(9)
addi 31,8,696
dcbtst 0,7
stw 11,72(9)
stw 12,76(9)
addi 30,8,704
dcbtst 0,6
stw 11,80(9)
stw 12,84(9)
addi 29,8,712
dcbtst 0,5
stw 11,88(9)
stw 12,92(9)
addi 28,8,720
dcbtst 0,4
stw 11,96(9)
stw 12,100(9)
addi 27,8,728
dcbtst 0,3
stw 11,104(9)
stw 12,108(9)
addi 26,8,736
dcbtst 0,31
stw 11,112(9)
stw 12,116(9)
addi 25,8,744
dcbtst 0,30
stw 11,120(9)
stw 12,124(9)
addi 24,8,752
dcbtst 0,29
stw 11,128(9)
stw 12,132(9)
addi 21,8,760
dcbtst 0,28
stw 11,8(10)
stw 12,12(10)
addi 22,8,768
dcbtst 0,27
stw 11,16(10)
stw 12,20(10)
addi 23,8,776
dcbtst 0,26
stw 11,120(10)
stw 12,124(10)
addi 7,8,784
dcbtst 0,25
stw 11,24(10)
stw 12,28(10)
addi 6,8,792
dcbtst 0,24
stw 11,32(10)
stw 12,36(10)
addi 5,8,800
dcbtst 0,21
stw 11,40(10)
stw 12,44(10)
addi 21,8,888
dcbtst 0,23
stw 11,48(10)
stw 12,52(10)
addi 4,8,808
dcbtst 0,7
stw 11,56(10)
stw 12,60(10)
addi 3,8,816
dcbtst 0,6
stw 11,64(10)
stw 12,68(10)
addi 31,8,824
dcbtst 0,5
stw 11,72(10)
stw 12,76(10)
addi 30,8,832
dcbtst 0,4
stw 11,80(10)
stw 12,84(10)
addi 29,8,840
dcbtst 0,3
stw 11,88(10)
stw 12,92(10)
addi 28,8,848
dcbtst 0,31
stw 11,96(10)
stw 12,100(10)
addi 27,8,856
dcbtst 0,30
stw 11,104(10)
stw 12,108(10)
addi 26,8,864
dcbtst 0,29
stw 11,112(10)
stw 12,116(10)
addi 10,8,384
dcbtst 0,28
stw 11,384(8)
stw 12,388(8)
addi 25,8,872
dcbtst 0,27
stw 11,8(10)
stw 12,12(10)
addi 24,8,880
dcbtst 0,26
stw 11,16(10)
stw 12,20(10)
dcbtst 0,25
dcbtst 0,21
dcbtst 0,24
dcbtst 0,22
stw 11,120(10)
stw 12,124(10)
stw 11,24(10)
stw 12,28(10)
stw 11,32(10)
stw 12,36(10)
stw 11,40(10)
stw 12,44(10)
stw 11,48(10)
stw 12,52(10)
stw 11,56(10)
stw 12,60(10)
stw 11,64(10)
stw 12,68(10)
stw 11,72(10)
stw 12,76(10)
stw 11,80(10)
stw 12,84(10)
stw 11,88(10)
stw 12,92(10)
stw 11,96(10)
stw 12,100(10)
stw 11,104(10)
stw 12,108(10)
stw 11,112(10)
stw 12,116(10)
addi 10,8,512
stw 11,512(8)
stw 12,516(8)
stw 11,8(10)
stw 12,12(10)
stw 11,16(10)
stw 12,20(10)
stw 11,24(10)
stw 12,28(10)
stw 11,120(10)
stw 12,124(10)
stw 11,32(10)
stw 12,36(10)
stw 11,40(10)
stw 12,44(10)
stw 11,48(10)
stw 12,52(10)
stw 11,56(10)
stw 12,60(10)
stw 11,64(10)
stw 12,68(10)
stw 11,72(10)
stw 12,76(10)
stw 11,80(10)
stw 12,84(10)
stw 11,88(10)
stw 12,92(10)
stw 11,96(10)
stw 12,100(10)
stw 11,104(10)
stw 12,108(10)
stw 11,112(10)
stw 12,116(10)
addi 10,8,640
stw 11,640(8)
stw 12,644(8)
stw 11,120(10)
stw 12,124(10)
stw 11,8(10)
stw 12,12(10)
stw 11,16(10)
stw 12,20(10)
stw 11,24(10)
stw 12,28(10)
stw 11,32(10)
stw 12,36(10)
stw 11,40(10)
stw 12,44(10)
stw 11,48(10)
stw 12,52(10)
stw 11,56(10)
stw 12,60(10)
stw 11,64(10)
stw 12,68(10)
stw 11,72(10)
stw 12,76(10)
stw 11,80(10)
stw 12,84(10)
stw 11,88(10)
stw 12,92(10)
stw 11,96(10)
stw 12,100(10)
stw 11,104(10)
stw 12,108(10)
stw 11,112(10)
stw 12,116(10)
mr 8,22
bdnz .L2
li 3,0
lwz 21,20(1)
lwz 22,24(1)
lwz 23,28(1)
lwz 24,32(1)
lwz 25,36(1)
lwz 26,40(1)
lwz 27,44(1)
lwz 28,48(1)
lwz 29,52(1)
lwz 30,56(1)
lwz 31,60(1)
addi 1,1,64
blr
--
Summary: Over Aggressive Use of Data Cache Touch Instructions
During FDO
Product: gcc
Version: 4.0.0
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: target
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: steinmtz at us dot ibm dot com
CC: gcc-bugs at gcc dot gnu dot org,steinmtz at us dot ibm
dot com
GCC build triplet: powerpc64-linux
GCC host triplet: powerpc64-linux
GCC target triplet: powerpc64-linux
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17950
