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Re: arguements used in .c.26.flow2 are not used in assembly codes
- From: Ian Lance Taylor <ian at airs dot com>
- To: Liu Haibin <liu dot haibin at gmail dot com>
- Cc: gcc at gcc dot gnu dot org
- Date: 22 Sep 2005 13:21:00 -0700
- Subject: Re: arguements used in .c.26.flow2 are not used in assembly codes
- References: <e538aa3e05092203453c82d528@mail.gmail.com>
Liu Haibin <liu.haibin@gmail.com> writes:
> I compiled the following code using nios gcc -da -O3 (gcc version 3.3.3)
>
> #include <math.h>
> #define PI (4*atan(1))
>
> double rad2deg(double rad)
> {
> return (180.0 * rad / (PI));
> }
>
> The begining of the .s file is
> rad2deg:
> addi sp, sp, -16
> stw fp, 8(sp)
> mov r6, zero
> mov fp, sp
> movhi r7, %hiadj(1080459264)
> addi r7, r7, %lo(1080459264)
> stw ra, 12(sp)
> stw r16, 4(sp)
> stw r17, 0(sp)
> call __muldf3
> mov r4, zero
> movhi r5, %hiadj(1072693248)
> addi r5, r5, %lo(1072693248)
> mov r16, r2
> mov r17, r3
> call atan
> ......
>
> The corresponding rtl to "call __muldf3" in .c.26.flow2 file is
>
> (call_insn/u 17 16 21 0 0x0 (parallel [
> (set (reg:DF 2 r2)
> (call (mem:QI (symbol_ref:SI ("__muldf3")) [0 S1 A8])
> (const_int 0 [0x0])))
> (clobber (reg:SI 31 ra))
> ]) 44 {*call_value} (insn_list 15 (nil))
> (expr_list:REG_DEAD (reg:DF 4 r4)
> (expr_list:REG_DEAD (reg:DF 6 r6)
> (expr_list:REG_UNUSED (reg:SI 31 ra)
> (expr_list:REG_EH_REGION (const_int -1 [0xffffffff])
> (nil)))))
> (expr_list (use (reg:DF 6 r6))
> (expr_list (use (reg:DF 4 r4))
> (nil))))
>
> According to the rtl, it uses r4, r5, r6 and r7 as arguements. But the
> assemble codes show no r4 or r5 is ever used before "call __muldf3".
> Any idea why it is so?
Presumably r4 and r5 hold the value of rad which was passed into the
function. The compiler loads 180.0 into r6 and r7, and calls muldf3
to multiply rad (in r4/r5) by 180.0 (in r6/r7).
Ian