https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107949
Bug ID: 107949
Summary: PPC: Unnecessary rlwinm after lbzx
Product: gcc
Version: 12.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: jens.seifert at de dot ibm.com
Target Milestone: ---
extern unsigned char magic1[256];
unsigned int hash(const unsigned char inp[4])
{
const unsigned long long INIT = 0x1ULL;
unsigned long long h1 = INIT;
h1 = magic1[((unsigned long long)inp[0]) ^ h1];
h1 = magic1[((unsigned long long)inp[1]) ^ h1];
h1 = magic1[((unsigned long long)inp[2]) ^ h1];
h1 = magic1[((unsigned long long)inp[3]) ^ h1];
return h1;
}
#ifdef __powerpc__
#define lbzx(b,c) ({ unsigned long long r; __asm__("lbzx
%0,%1,%2":"=r"(r):"b"(b),"r"(c)); r; })
unsigned int hash2(const unsigned char inp[4])
{
const unsigned long long INIT = 0x1ULL;
unsigned long long h1 = INIT;
h1 = lbzx(magic1, inp[0] ^ h1);
h1 = lbzx(magic1, inp[1] ^ h1);
h1 = lbzx(magic1, inp[2] ^ h1);
h1 = lbzx(magic1, inp[3] ^ h1);
return h1;
}
#endif
Extra rlwinm get added.
hash(unsigned char const*):
.LCF0:
addi 2,2,.TOC.-.LCF0@l
lbz 9,0(3)
addis 10,2,.LC0@toc@ha
ld 10,.LC0@toc@l(10)
lbz 6,1(3)
lbz 7,2(3)
lbz 8,3(3)
xori 9,9,0x1
lbzx 9,10,9
xor 9,9,6
rlwinm 9,9,0,0xff <= not necessary
lbzx 9,10,9
xor 9,9,7
rlwinm 9,9,0,0xff <= not necessary
lbzx 9,10,9
xor 9,9,8
rlwinm 9,9,0,0xff <= not necessary
lbzx 3,10,9
blr
.long 0
.byte 0,9,0,0,0,0,0,0
hash2(unsigned char const*):
.LCF1:
addi 2,2,.TOC.-.LCF1@l
lbz 7,0(3)
lbz 8,1(3)
lbz 10,2(3)
lbz 6,3(3)
addis 9,2,.LC1@toc@ha
ld 9,.LC1@toc@l(9)
xori 7,7,0x1
lbzx 7,9,7
xor 8,8,7
lbzx 8,9,8
xor 10,10,8
lbzx 10,9,10
xor 10,6,10
lbzx 3,9,10
rldicl 3,3,0,32
blr
Tiny sample:
unsigned long long tiny(const unsigned char *inp)
{
return inp[0] ^ inp[1];
}
tiny(unsigned char const*):
lbz 9,0(3)
lbz 10,1(3)
xor 3,9,10
rlwinm 3,3,0,0xff
blr
.long 0
.byte 0,9,0,0,0,0,0,0
unsigned long long tiny2(const unsigned char *inp)
{
unsigned long long a = inp[0];
unsigned long long b = inp[1];
return a ^ b;
}
tiny2(unsigned char const*):
lbz 9,0(3)
lbz 10,1(3)
xor 3,9,10
rlwinm 3,3,0,0xff
blr
.long 0
.byte 0,9,0,0,0,0,0,0
lbz/lbzx creates a value 0 <= x < 256. xor of 2 such values does not change
value range.
