------- Comment #6 from steven at gcc dot gnu dot org 2006-01-02 21:27 -------
Ehm, wouldn't "unsigned char *" alias everything? GCSE doesn't do load PRE for
me on the original test case, either. And, as long as "outbuf[outcnt] =
bi_buf;" has a V_MAY_DEF for outcnt, you're not going to see any load PRE
happening here.
With a changed test case, GCSE _does_ perform load PRE:
unsigned long outcnt;
extern void flush_outbuf(void);
void
bi_windup(unsigned int *outbuf, unsigned int bi_buf)
{
unsigned long t1 = outcnt;
outbuf[t1] = bi_buf;
unsigned long t2 = outcnt;
if (t2 == 16384)
flush_outbuf();
unsigned long t3 = outcnt;
outbuf[t3] = bi_buf;
}
This gives me the following asm on x86-64:
bi_windup:
movq %rbx, -16(%rsp)
movq %rbp, -8(%rsp)
subq $24, %rsp
movq outcnt(%rip), %rax
movq %rdi, %rbp
movl %esi, %ebx
cmpq $16384, %rax
movl %esi, (%rbp,%rax,4)
je .L6
.L2:
movl %ebx, (%rbp,%rax,4)
movq 8(%rsp), %rbx
movq 16(%rsp), %rbp
addq $24, %rsp
ret
.p2align 4,,7
.L6:
call flush_outbuf
movq outcnt(%rip), %rax
jmp .L2
Looking at the .pre tree dump, there isn't anything obvious in the way of doing
load PRE here AFAICT:
bi_windup (outbufD.1866, bi_bufD.1867)
{
unsigned intD.3 storetmp.21D.1918;
long unsigned intD.4 t3D.1872;
long unsigned intD.4 t2D.1871;
long unsigned intD.4 t1D.1870;
unsigned intD.3 * D.1878;
unsigned intD.3 * D.1877;
long unsigned intD.4 D.1876;
unsigned intD.3 * D.1875;
unsigned intD.3 * D.1874;
long unsigned intD.4 D.1873;
# BLOCK 2 freq:10000
# PRED: ENTRY [100.0%] (fallthru,exec)
# VUSE <outcntD.1863_1>;
t1D.1870_2 = outcntD.1863;
D.1873_3 = t1D.1870_2 * 4;
D.1874_4 = (unsigned intD.3 *) D.1873_3;
D.1875_6 = D.1874_4 + outbufD.1866_5;
# TMT.4D.1900_16 = V_MAY_DEF <TMT.4D.1900_15>;
*D.1875_6 = bi_bufD.1867_7;
if (t1D.1870_2 == 16384) goto <L0>; else goto <L2>;
# SUCC: 3 [26.2%] (true,exec) 5 [73.8%] (false,exec)
# BLOCK 5 freq:7378
# PRED: 2 [73.8%] (false,exec)
<L2>:;
goto <bb 4> (<L1>);
# SUCC: 4 [100.0%] (fallthru)
# BLOCK 3 freq:2622
# PRED: 2 [26.2%] (true,exec)
<L0>:;
# outcntD.1863_18 = V_MAY_DEF <outcntD.1863_1>;
# TMT.4D.1900_19 = V_MAY_DEF <TMT.4D.1900_16>;
flush_outbuf ();
# SUCC: 4 [100.0%] (fallthru,exec)
# BLOCK 4 freq:10000
# PRED: 5 [100.0%] (fallthru) 3 [100.0%] (fallthru,exec)
# TMT.4D.1900_14 = PHI <TMT.4D.1900_16(5), TMT.4D.1900_19(3)>;
# outcntD.1863_13 = PHI <outcntD.1863_1(5), outcntD.1863_18(3)>;
<L1>:;
# VUSE <outcntD.1863_13>;
t3D.1872_9 = outcntD.1863;
D.1876_10 = t3D.1872_9 * 4;
D.1877_11 = (unsigned intD.3 *) D.1876_10;
D.1878_12 = D.1877_11 + outbufD.1866_5;
# TMT.4D.1900_17 = V_MAY_DEF <TMT.4D.1900_14>;
*D.1878_12 = bi_bufD.1867_7;
return;
# SUCC: EXIT [100.0%]
}
--
steven at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |TREE
Summary|load PRE is missing |tree load PRE is not working
| |properly
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23455
