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[Bug target/26525] New: missed opportunity to use value in fp reg
- From: "amodra at bigpond dot net dot au" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 2 Mar 2006 02:40:57 -0000
- Subject: [Bug target/26525] New: missed opportunity to use value in fp reg
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
The following compiled with -m64 -O2 -S
double f1 (double xh)
{
long long hi = (long long) xh;
if (hi == __LONG_LONG_MAX__)
{
xh += -__LONG_LONG_MAX__ - 1;
xh += 1.0;
}
else
xh -= hi;
return xh;
}
generates
fctidz 0,1
li 0,-1
rldicl 0,0,0,1
stfd 0,-16(1)
ld 9,-16(1)
cmpd 7,9,0
beq 7,.L7
std 9,-16(1) #
nop #
nop #
nop #
lfd 13,-16(1) #
fcfid 0,13 #
fsub 1,1,0
blr
.p2align 4,,15
.L7:
lfs 0,.LC1@toc(2)
lfs 13,.LC3@toc(2)
fsub 0,1,0
fadd 1,0,13
blr
The sequence marked with # could be replaced with just one insn,
fcfid 0,0
because HI is in fr0 at that point.
A similar function
double f2 (double xh)
{
long long hi = (long long) xh;
xh -= hi;
if (hi == __LONG_LONG_MAX__)
{
xh += hi;
xh += -__LONG_LONG_MAX__ - 1;
xh += 1.0;
}
return xh;
}
does use the value in th fp reg
fctidz 0,1
li 0,-1
rldicl 0,0,0,1
stfd 0,-16(1)
fcfid 0,0 <== here
fsub 1,1,0
ld 9,-16(1)
cmpd 7,9,0
bnelr 7
fadd 0,0,1
lfs 13,.LC5@toc(2)
lfs 12,.LC7@toc(2)
fsub 0,0,13
fadd 1,0,12
blr
--
Summary: missed opportunity to use value in fp reg
Product: gcc
Version: 4.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: amodra at bigpond dot net dot au
GCC target triplet: powerpc64-linux
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26525