http://gcc.gnu.org/bugzilla/show_bug.cgi?id=61032
Bug ID: 61032
Summary: rs6000 code gen suffers from lack of address_cost
Product: gcc
Version: 4.10.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: amodra at gmail dot com
-mcmodel=medium introduced a code model where addresses typically need two
instructions. As illustrated in the following, the fact that rs6000 lacks an
address_cost function to say that UNSPEC_TOCREL addresses are more costly than
say, register indirect, sees fwprop making poor decisions.
struct fourlongs {
long l[4];
} x, y;
void f1(void)
{
void *a = &x;
void *b = &y;
__builtin_memcpy (a, b, sizeof(x));
}
/* -O2 -S -fvisibility-hidden
.L.f1:
addis 7,2,y@toc@ha
addis 8,2,y+8@toc@ha
addis 6,2,x@toc@ha
addis 10,2,y+16@toc@ha
ld 7,y@toc@l(7)
ld 8,y+8@toc@l(8)
addis 9,2,y+24@toc@ha
ld 10,y+16@toc@l(10)
ld 9,y+24@toc@l(9)
std 7,x@toc@l(6)
addis 7,2,x+8@toc@ha
std 8,x+8@toc@l(7)
addis 8,2,x+16@toc@ha
std 10,x+16@toc@l(8)
addis 10,2,x+24@toc@ha
std 9,x+24@toc@l(10)
blr
*/
void f2(void)
{
void *a = &x;
void *b = &y;
__asm__ ("" : "+r" (a));
__asm__ ("" : "+r" (b));
__builtin_memcpy (a, b, sizeof(x));
}
/* -O2 -S -fvisibility-hidden
fewer dependent address calcs, mem loads earlier and back-to-back, smaller
code
.L.f2:
addis 9,2,y@toc@ha
addi 9,9,y@toc@l
ld 6,0(9)
ld 7,8(9)
ld 8,16(9)
ld 10,24(9)
addis 9,2,x@toc@ha
addi 9,9,x@toc@l
std 6,0(9)
std 7,8(9)
std 8,16(9)
std 10,24(9)
blr
*/
