Aucbvax.6857
fa.info-vax
utzoo!decvax!ucbvax!info-vax
Thu Apr 22 09:30:57 1982
unix cc and float registers
>From dove@mit-dspg@mit-mc Thu Apr 22 09:22:29 1982
The following results were obtained from mit-vax (berkeley 4.1 I think).
The adb files were taken from a.out. The only compiler switch was -O.
---junkc.c---
main()
{
register double z=0, x=1;
register int i=100000;
while(i-->0)
{
z += x;
z += x;
z += x;
z += x;
z += x;
z += x;
z += x;
z += x;
z += x;
z += x;
}
}
---junkc.adb----
_main:
_main: 800
3e: subl2 $10,sp
41: movd _environ+4,-8(fp)
49: movd _environ+c,-10(fp)
51: movl $186a0,r11
58: brb 8c
5a: addd2 -10(fp),-8(fp)
5f: addd2 -10(fp),-8(fp)
64: addd2 -10(fp),-8(fp)
69: addd2 -10(fp),-8(fp)
6e: addd2 -10(fp),-8(fp)
73: addd2 -10(fp),-8(fp)
78: addd2 -10(fp),-8(fp)
7d: addd2 -10(fp),-8(fp)
82: addd2 -10(fp),-8(fp)
87: addd2 -10(fp),-8(fp)
8c: movl r11,r0
8f: decl r11
91: tstl r0
93: bgtr 5a
95: ret
96: halt
97: halt
_exit:
---junkp.p---
program junkp (input, output);
var z, x :real;
i : integer;
begin z := 0;
x := 1;
i := 100000;
while i>0 do
begin
z := z+x;
z := z+x;
z := z+x;
z := z+x;
z := z+x;
z := z+x;
z := z+x;
z := z+x;
z := z+x;
z := z+x;
i := i-1
end
end.
---junkp.adb---
_program:
_program: 0
66: subl2 $10,sp
69: moval _UNWIND,(fp)
70: moval __disply+8,-4(fp)
78: movq __disply+8,-c(fp)
80: movq ap,__disply+8
87: clrq _z
8d: cvtld $1,_x
94: movl $186a0,_i
9f: brb _program+b2
a1: addd2 _x,_z
ac: addd2 _x,_z
b7: addd2 _x,_z
c2: addd2 _x,_z
cd: addd2 _x,_z
d8: addd2 _x,_z
e3: addd2 _x,_z
ee: addd2 _x,_z
f9: addd2 _x,_z
_program+a0: addd2 _x,_z
_program+ab: subl2 $1,_i
_program+b2: tstl _i
_program+b8: bgtr a1
_program+ba: movq -c(fp),__disply+8
_program+c2: ret
_program+c3:
As you can see, registers don't get used for floating point.
Here is an equivalent program with ints instead of doubles, and it does the
right thing:
---junkci.c---
main()
{
register int z=0, x=1;
register int i;
for(i=0; i<100000; 51: 43: RET 5A: 3E: UNDERSTAND 60: +="x;" 45: C I++) 4E: Z 54: INCL R9,$186A0 5D: { } 63: 6C: FLOATS!) (WHEN MOVL 48: 65: 57: R9 R10,R11 6E: 45 6F:
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