On 07/26/2018 12:06 AM, 瞿仙淼 wrote:
I wrote a case to reproduce this problem on C-SKY. C code is as follows:
-----------------------------------------------------------------------
int e1, e2;
void func (int a, int b, int c, int d, int f, int g)
{
e1 = a > b ? f : g;
e2 = a > b ? c : d;
return;
}
-----------------------------------------------------------------------
compile to assembler with option “-O3 -S” :
-----------------------------------------------------------------------
func:
cmplt a1, a0
ld.w t1, (sp, 0)
ld.w t0, (sp, 4)
movt t0, t1
cmplt a1, a0
movt a3, a2
lrw a1, e2
lrw a2, e1
st.w a3, (a1, 0)
st.w t0, (a2, 0)
rts
-----------------------------------------------------------------------
There is an extra “cmplt a1, a0" in the above code without cse_cc. This
situation mainly occurs when a relatively short branch jump is converted into a
conditional execution instruction. And the CSE pass can not reduce the same
conditional comparison instruction . Here is the rtx sequence after “cse2” pass.
-----------------------------------------------------------------------
(insn 28 13 29 2 (set (reg:CC 33 c)
(gt:CC (reg/v:SI 77 [ a ])
(reg/v:SI 78 [ b ]))) func.c:5 1099 {*cmpgtsi}
(nil))
(insn 29 28 30 2 (set (reg/v:SI 82 [ g ])
(if_then_else:SI (eq (reg:CC 33 c)
(const_int 0 [0]))
(reg/v:SI 82 [ g ])
(reg/v:SI 81 [ f ]))) func.c:5 983 {movf}
(expr_list:REG_DEAD (reg/v:SI 81 [ f ])
(expr_list:REG_DEAD (reg:CC 33 c)
(nil))))
(insn 30 29 31 2 (set (reg:CC 33 c)
(gt:CC (reg/v:SI 77 [ a ])
(reg/v:SI 78 [ b ]))) func.c:5 1099 {*cmpgtsi}
(expr_list:REG_DEAD (reg/v:SI 78 [ b ])
(expr_list:REG_DEAD (reg/v:SI 77 [ a ])
(nil))))
(insn 31 30 18 2 (set (reg/v:SI 80 [ d ])
(if_then_else:SI (eq (reg:CC 33 c)
(const_int 0 [0]))
(reg/v:SI 80 [ d ])
(reg/v:SI 79 [ c ]))) func.c:5 983 {movf}
(expr_list:REG_DEAD (reg/v:SI 79 [ c ])
(expr_list:REG_DEAD (reg:CC 33 c)
(nil))))
-----------------------------------------------------------------------
It doesn't seem to check the same conditional comparison instruction .So I
wrote this to solve this problem, but I am not sure if this is the best way : )
PS, the same conditional comparison instruction cannot be reduced with the
latest version gcc with C-SKY because I just insert the “cse_cc” after “cse1”,
when I insert after “cse2”, this problem can be solved very well.
Thanks, this is very helpful. I've verified this and I'm moving the
pass as you suggest, adding a more detailed comment to the source to
explain what the pass is for, and adding your test case to the
testsuite. This will be included when I resubmit the patches to address
other review comments too.
Jeff, does that adequately address your concerns about whether the pass
is useful?
-Sandra
