http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50749
bin.cheng <amker.cheng at gmail dot com> changed:
What |Removed |Added
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CC| |amker.cheng at gmail dot com
--- Comment #15 from bin.cheng <amker.cheng at gmail dot com> ---
There must be another scenario for the example, and in this case example:
int test_0 (char* p, int c)
{
int r = 0;
r += *p++;
r += *p++;
r += *p++;
return r;
}
should be translated into sth like:
//...
ldrb [rx]
ldrb [rx+1]
ldrb [rx+2]
add rx, rx, #3
//...
This way all loads are independent and can be issued on super scalar machine.
Actuall for targets like arm which supports post-increment constant (other than
size of memory access), it can be further changed into:
//...
ldrb [rx], #3
ldrb [rx-2]
ldrb [rx-1]
//...
For now auto-increment pass can't do this optimization. I once have a patch
for this but benchmark shows the case is not common.
This case is common especially after loop unrolling and rtl passes deliberately
break down long dependence of RX, which I think is right.
