Hi,
Consider code:
int foo(char *t, char *v, int w)
{
int i;
for (i = 1; i != w; ++i)
{
int x = i 2;
v[x + 4] = t[x + 4];
}
return 0;
}
Compile it to x86 (I used both gcc 4.7.2 and gcc 4.8.1) with options:
gcc -O2 -m32 -S test.c
You will see loop, formed like:
.L5:
leal 0(,%eax,4), %edx
On 06/12/13 09:30, Konstantin Vladimirov wrote:
Hi,
Consider code:
int foo(char *t, char *v, int w)
{
int i;
for (i = 1; i != w; ++i)
{
int x = i 2;
v[x + 4] = t[x + 4];
}
return 0;
}
Compile it to x86 (I used both gcc 4.7.2 and gcc 4.8.1) with options:
gcc -O2 -m32 -S
Hi,
Example from x86 code was only for ease of reproduction. I am pretty
sure, this is architecture-independent issue. Say on ARM:
.L2:
mov ip, r3, asl #2
add ip, ip, #4
add r3, r3, #1
ldrb r4, [r0, ip] @ zero_extendqisi2
cmp r3, r2
strb r4, [r1, ip]
bne .L2
May be improved to:
.L2:
add r3,
On Fri, Dec 06, 2013 at 12:30:54PM +0400, Konstantin Vladimirov wrote:
Consider code:
int foo(char *t, char *v, int w)
{
int i;
for (i = 1; i != w; ++i)
{
int x = i 2;
v[x + 4] = t[x + 4];
}
return 0;
}
This is either job of ivopts pass, dunno why it doesn't consider
turning
On Fri, Dec 6, 2013 at 9:30 AM, Konstantin Vladimirov
konstantin.vladimi...@gmail.com wrote:
Hi,
Consider code:
int foo(char *t, char *v, int w)
{
int i;
for (i = 1; i != w; ++i)
{
int x = i 2;
v[x + 4] = t[x + 4];
}
return 0;
}
Compile it to x86 (I used both gcc 4.7.2 and gcc
Hi,
nothing changes if everything is unsigned and we are guaranteed to not
raise UB on overflow:
unsigned foo(unsigned char *t, unsigned char *v, unsigned w)
{
unsigned i;
for (i = 1; i != w; ++i)
{
unsigned x = i 2;
v[x + 4] = t[x + 4];
}
return 0;
}
yields:
.L5:
leal 0(,%eax,4), %edx
addl
On Fri, Dec 6, 2013 at 11:19 AM, Konstantin Vladimirov
konstantin.vladimi...@gmail.com wrote:
Hi,
nothing changes if everything is unsigned and we are guaranteed to not
raise UB on overflow:
unsigned foo(unsigned char *t, unsigned char *v, unsigned w)
{
unsigned i;
for (i = 1; i != w;
On Fri, Dec 6, 2013 at 2:25 AM, Richard Biener
richard.guent...@gmail.com wrote:
On Fri, Dec 6, 2013 at 11:19 AM, Konstantin Vladimirov
konstantin.vladimi...@gmail.com wrote:
Hi,
nothing changes if everything is unsigned and we are guaranteed to not
raise UB on overflow:
unsigned
On Fri, 6 Dec 2013, Konstantin Vladimirov wrote:
Consider code:
int foo(char *t, char *v, int w)
{
int i;
for (i = 1; i != w; ++i)
{
int x = i 2;
A side note, but something too few people seem to be aware of: writing
i2 can pessimize code compared to i*4 (and it is never faster). That is
Hi,
Richard, I tried to add LSHIFT_EXPR case to tree-scalar-evolution.c
and now it yields code like (x86 again):
.L5:
movzbl 4(%esi,%eax,4), %edx
movb %dl, 4(%ebx,%eax,4)
addl $1, %eax
cmpl %ecx, %eax
jne .L5
So, excessive lea is gone. It is great, thank you so much. But I
wonder what else can
On Fri, Dec 6, 2013 at 2:52 PM, Konstantin Vladimirov
konstantin.vladimi...@gmail.com wrote:
Hi,
Richard, I tried to add LSHIFT_EXPR case to tree-scalar-evolution.c
and now it yields code like (x86 again):
.L5:
movzbl 4(%esi,%eax,4), %edx
movb %dl, 4(%ebx,%eax,4)
addl $1, %eax
cmpl %ecx,
On 12/06/13 07:17, Richard Biener wrote:
On Fri, Dec 6, 2013 at 2:52 PM, Konstantin Vladimirov
konstantin.vladimi...@gmail.com wrote:
Hi,
Richard, I tried to add LSHIFT_EXPR case to tree-scalar-evolution.c
and now it yields code like (x86 again):
.L5:
movzbl 4(%esi,%eax,4), %edx
movb %dl,
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